Features• High Performance, Low Power AVR® 8-Bit Microcontroller• Advanced RISC Architecture– 125 Powerful Instructions – Most Single Clock Cycle Execution– 32 x 8 General Purpose Working Registers– Fully Static Operation– Up to 16 MIPS Throughput at 16 MHz• Non-volatile Program and Data Memories– 8K / 16K Bytes of In-System Self-Programmable Flash• Endurance: 10,000 Write/Erase Cycles– Optional Boot Code Section with Independent Lock Bits
• USB boot-loader programmed by default in the factory• In-System Programming by on-chip Boot Program hardware-activated after
reset• True Read-While-Write Operation– 512 Bytes EEPROM• Endurance: 100,000 Write/Erase Cycles– 512 Bytes Internal SRAM
– Programming Lock for Software Security• USB 2.0 Full-speed Device Module with Interrupt on Transfer Completion– Complies fully with Universal Serial Bus Specification REV 2.0– 48 MHz PLL for Full-speed Bus Operation : data transfer rates at 12 Mbit/s– Fully independant 176 bytes USB DPRAM for endpoint memory allocation– Endpoint 0 for Control Transfers: from 8 up to 64-bytes– 4 Programmable Endpoints:• IN or Out Directions• Bulk, Interrupt and IsochronousTransfers• Programmable maximum packet size from 8 to 64 bytes• Programmable single or double buffer– Suspend/Resume Interrupts– Microcontroller reset on USB Bus Reset without detach– USB Bus Disconnection on Microcontroller Request– USB pad multiplexed with PS/2 peripheral for single cable capability• Peripheral Features– PS/2 compliant pad– One 8-bit Timer/Counters with Separate Prescaler and Compare Mode (two 8-bit
PWM channels)– One 16-bit Timer/Counter with Separate Prescaler, Compare and Capture Mode
(three 8-bit PWM channels)– USART with SPI master only mode and hardware flow control (RTS/CTS)– Master/Slave SPI Serial Interface– Programmable Watchdog Timer with Separate On-chip Oscillator– On-chip Analog Comparator– Interrupt and Wake-up on Pin Change• On Chip Debug Interface (debugWIRE)• Special Microcontroller Features– Power-On Reset and Programmable Brown-out Detection– Internal Calibrated Oscillator– External and Internal Interrupt Sources

8-bit
Microcontroller
with
8/16K Bytes of
ISP Flash
and USB
Controller
AT90USB82
AT90USB162

7707E–AVR–11/08

– Five Sleep Modes: Idle, Power-save, Power-down, Standby, and Extended Standby• I/O and Packages– 22 Programable I/O Lines– QFN32 (5x5mm) / TQFP32 packages• Operating Voltages– 2.7 - 5.5V
• Operating temperature– Industrial (-40°C to +85°C)• Maximum Frequency– 8 MHz at 2.7V - Industrial range– 16 MHz at 4.5V - Industrial range

2

AT90USB82/162

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AT90USB82/162
1. Pin Configurations

PC5 ( PCINT9/ OC.1B)

UGND

Pinout AT90USB82/162

UCAP
PC4 (PCINT10)

D+ / SCK

AVCC
UVCC
D- / SDATA

Figure 1-1.

32 31 30 29 28 27 26 25
Reset (PC1 / dW)

PB6 (PCINT6)
PB4 (T1 / PCINT4)

UGND

AVCC
UVCC
D- / SDATA(SCLK / PCINT1) PB1(PDI / MOSI / PCINT2) PB2(SS / PCINT0) PB0

D+ / SCK

PB3 (PDO / MISO / PCINT3)

UCAP
PC4 (PCINT10)PB5 (PCINT5)PC5 ( PCINT9/ OC.1B)

PC6 (OC.1A / PCINT8)PC7 (INT4 / ICP1 / CLKO)
PB7 (PCINT7 / OC.0A / OC.1C)

9 10 11 12 13 14 15 16(TXD1 / INT3) PD3(AIN0 / INT1) PD1(RXD1 / AIN1 / INT2) PD2

24
23
22
21
20
19
18
17

QFN32

(RTS / INT6) PD6(CTS / HWB / T0 / INT7) PD7

VCC(PCINT11) PC2(OC.0B / INT0) PD0

1
2
3
4
5
6
7
8

(INT5) PD4(XCK / PCINT12) PD5

XTAL1(PC0) XTAL2
GND

32 31 30 29 28 27 26 25
XTAL1(PC0) XTAL2
GND
VCC(PCINT11) PC2(OC.0B / INT0) PD0(AIN0 / INT1) PD1(RXD1 / AIN1 / INT2) PD2

1
2
3
4
5
6
7
8

TQFP32

24
23
22
21
20
19
18
17

Reset (PC1 / dW)
PC6 (OC.1A / PCINT8)PC7 (INT4 / ICP1 / CLKO)
PB7 (PCINT7 / OC.0A / OC.1C)
PB6 (PCINT6)
PB5 (PCINT5)
PB4 (T1 / PCINT4)
PB3 (PDO / MISO / PCINT3)

Note:

1.1

(SCLK / PCINT1) PB1(PDI / MOSI / PCINT2) PB2(SS / PCINT0) PB0(RTS / INT6) PD6(CTS / HWB / T0 / INT7) PD7(INT5) PD4(XCK / PCINT12) PD5(TXD1 / INT3) PD3

9 10 11 12 13 14 15 16

The large center pad underneath the QFN packages is made of metal and must be connected to
GND. It should be soldered or glued to the board to ensure good mechanical stability. If the center
pad is left unconnected, the package might loosen from the board.

Disclaimer
Typical values contained in this datasheet are based on simulations and characterization ofother AVR microcontrollers manufactured on the same process technology. Min and Max values
will be available after the device is characterized.

37707E–AVR–11/08

2. Overview
The AT90USB82/162 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the AT90USB82/162 achieves throughputs approaching 1 MIPS per
MHz allowing the system designer to optimize power consumption versus processing speed.

Block Diagram

Figure 2-1.

+
ANALOGCOMPARATORPORTC DRIVERS

PORTD DRIVERSDATA REGISTER
PORTD

PB7 - PB0

PC7 - PC0DATA DIR.
REG. PORTDDATA REGISTER
PORTC

RESET

PD7 - PD0XTAL2Block Diagram

XTAL1

2.1

PORTB DRIVERSDATA DIR.
REG. PORTCDATA REGISTERPORTBDATA DIR.
REG. PORTB

8-BIT DA TA BUS

VCC

POR - BOD
RESET

GND

Debug-Wire

PROGRAM
COUNTER

STACK
POINTER

ON-CHIP DEBUG

PROGRAM
FLASH

SRAM

PROGRAMMINGLOGICINSTRUCTIONREGISTER

GENERALPURPOSEREGISTERSINTERNAL
OSCILLATORWATCHDOGTIMER

MCU CONTROLREGISTERCALIB. OSC

OSCILLATOR

TIMING AND
CONTROLTIMER/
COUNTERS
UVcc

X

INSTRUCTIONDECODERCONTROL
LINES

Y
Z

ALU

INTERRUPT
UNIT

ON-CHIP
3.3V
REGULATOR

UCap
1uF

EEPROM
PLL

STATUSREGISTERUSB

USART1SPI

D+/SCK
D-/SDATA

PS/2

The AVR core combines a rich instruction set with 32 general purpose working registers. All the
32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two independent
registers to be accessed in one single instruction executed in one clock cycle. The resulting

4

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
architecture is more code efficient while achieving throughputs up to ten times faster than conventional CISC microcontrollers.
The AT90USB82/162 provides the following features: 8K / 16K bytes of In-System Programmable Flash with Read-While-Write capabilities, 512 bytes EEPROM, 512 bytes SRAM, 22 general
purpose I/O lines, 32 general purpose working registers, two flexible Timer/Counters with compare modes and PWM, one USART, a programmable Watchdog Timer with Internal Oscillator,
an SPI serial port, debugWIRE interface, also used for accessing the On-chip Debug systemand programming and five software selectable power saving modes. The Idle mode stops the
CPU while allowing the SRAM, Timer/Counters, SPI port, and interrupt system to continue functioning. The Power-down mode saves the register contents but freezes the Oscillator, disabling
all other chip functions until the next interrupt or Hardware Reset. In Standby mode, the Crystal/Resonator Oscillator is running while the rest of the device is sleeping. This allows very fast
start-up combined with low power consumption. In Extended Standby mode, the main Oscillator
continues to run.
The device is manufactured using Atmel’s high-density nonvolatile memory technology. The onchip ISP Flash allows the program memory to be reprogrammed in-system through an SPI serialinterface, by a conventional nonvolatile memory programmer, or by an on-chip Boot program
running on the AVR core. The boot program can use any interface to download the application
program in the application Flash memory. Software in the Boot Flash section will continue to run
while the Application Flash section is updated, providing true Read-While-Write operation. By
combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a monolithic chip,
the Atmel AT90USB82/162 is a powerful microcontroller that provides a highly flexible and costeffective solution to many embedded control applications.
The AT90USB82/162 AVR is supported with a full suite of program and system development
tools including: C compilers, macro assemblers, program debugger/simulators, in-circuit emulators, and evaluation kits.

2.2
2.2.1

Pin Descriptions
VCC
Digital supply voltage.

2.2.2

GND
Ground.

2.2.3

Port B (PB7..PB0)
Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port B output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port B pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port B also serves the functions of various special features of the AT90USB82/162 as listed on
page 74.

57707E–AVR–11/08

2.2.4

Port C (PC7..PC0)
Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The
Port C output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port C pins are tri-stated when a reset condition becomes active,
even if the clock is not running.
Port C also serves the functions of various special features of the AT90USB82/162 as listed on
page 76.

2.2.5

Port D (PD7..PD0)
Port D serves as analog inputs to the analog comparator.
Port D also serves as an 8-bit bi-directional I/O port, if the analog comparator is not used (concerns PD2/PD1 pins). Port pins can provide internal pull-up resistors (selected for each bit). The
Port D output buffers have symmetrical drive characteristics with both high sink and source
capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up
resistors are activated. The Port D pins are tri-stated when a reset condition becomes active,
even if the clock is not running.

2.2.6

D-/SDATAUSB Full Speed Negative Data Upstream Port / Data port for PS/2

2.2.7

D+/SCKUSB Full Speed Positive Data Upstream Port / Clock port for PS/2

2.2.8

UGND
USB Ground.

2.2.9

UVCC
USB Pads Internal Regulator Input supply voltage.

2.2.10UCAP
USB Pads Internal Regulator Output supply voltage. Should be connected to an external capacitor (1µF).

2.2.11RESET/PC1/dW
Reset input. A low level on this pin for longer than the minimum pulse length will generate areset, even if the clock is not running. The minimum pulse length is given in Section 9.. Shorter
pulses are not guaranteed to generate a reset. This pin alternatively serves as debugWire channel or as generic I/O. The configuration depends on the fuses RSTDISBL and DWEN.

2.2.12

XTAL1
Input to the inverting Oscillator amplifier and input to the internal clock operating circuit.

2.2.13

XTAL2/PC0
Output from the inverting Oscillator amplifier if enabled by Fuse. Also serves as a generic I/O.

6

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
3. About Code Examples
This documentation contains simple code examples that briefly show how to use various parts ofthe device. Be aware that not all C compiler vendors include bit definitions in the header files
and interrupt handling in C is compiler dependent. Please confirm with the C compiler documentation for more details.
These code examples assume that the part specific header file is included before compilation.
For I/O registers located in extended I/O map, "IN", "OUT", "SBIS", "SBIC", "CBI", and "SBI"
instructions must be replaced with instructions that allow access to extended I/O. Typically"LDS" and "STS" combined with "SBRS", "SBRC", "SBR", and "CBR".

7
7707E–AVR–11/08

4. AVR CPU Core
4.1

Introduction
This section discusses the AVR core architecture in general. The main function of the CPU core
is to ensure correct program execution. The CPU must therefore be able to access memories,
perform calculations, control peripherals, and handle interrupts.

4.2

Architectural Overview
Figure 4-1.

Block Diagram of the AVR Architecture
Data Bus 8-bit

Flash
Program
MemoryProgram
Counter

Statusand Control

32 x 8GeneralPurposeRegistrers

Control Lines

Direct Addressing

Instruction
Decoder

Indirect Addressing

Instruction
RegisterInterrupt
Unit
SPI
Unit
Watchdog
Timer

ALU

AnalogComparator

I/O Module1
Data
SRAM

I/O Module 2

I/O Module n
EEPROM

I/O Lines

In order to maximize performance and parallelism, the AVR uses a Harvard architecture – withseparate memories and buses for program and data. Instructions in the program memory are
executed with a single level pipelining. While one instruction is being executed, the next instruction is pre-fetched from the program memory. This concept enables instructions to be executedin every clock cycle. The program memory is In-System Reprogrammable Flash memory.

8

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
The fast-access Register File contains 32 x 8-bit general purpose working registers with a single
clock cycle access time. This allows single-cycle Arithmetic Logic Unit (ALU) operation. In a typical ALU operation, two operands are output from the Register File, the operation is executed,
and the result is stored back in the Register File – in one clock cycle.
Six of the 32 registers can be used as three 16-bit indirect address register pointers for Data
Space addressing – enabling efficient address calculations. One of these address pointers canalso be used as an address pointer for look up tables in Flash program memory. These addedfunction registers are the 16-bit X-, Y-, and Z-register, described later in this section.
The ALU supports arithmetic and logic operations between registers or between a constant anda register. Single register operations can also be executed in the ALU. After an arithmetic operation, the Status Register is updated to reflect information about the result of the operation.
Program flow is provided by conditional and unconditional jump and call instructions, able todirectly address the whole address space. Most AVR instructions have a single 16-bit word format. Every program memory address contains a 16- or 32-bit instruction.
Program Flash memory space is divided in two sections, the Boot Program section and theApplication Program section. Both sections have dedicated Lock bits for write and read/write
protection. The SPM instruction that writes into the Application Flash memory section must
reside in the Boot Program section.
During interrupts and subroutine calls, the return address Program Counter (PC) is stored on the
Stack. The Stack is effectively allocated in the general data SRAM, and consequently the Stacksize is only limited by the total SRAM size and the usage of the SRAM. All user programs must
initialize the SP in the Reset routine (before subroutines or interrupts are executed). The Stack
Pointer (SP) is read/write accessible in the I/O space. The data SRAM can easily be accessed
through the five different addressing modes supported in the AVR architecture.
The memory spaces in the AVR architecture are all linear and regular memory maps.
A flexible interrupt module has its control registers in the I/O space with an additional Global
Interrupt Enable bit in the Status Register. All interrupts have a separate Interrupt Vector in theInterrupt Vector table. The interrupts have priority in accordance with their Interrupt Vector position. The lower the Interrupt Vector address, the higher the priority.
The I/O memory space contains 64 addresses for CPU peripheral functions as Control Registers, SPI, and other I/O functions. The I/O Memory can be accessed directly, or as the Data
Space locations following those of the Register File, 0x20 - 0x5F. In addition, theAT90USB82/162 has Extended I/O space from 0x60 - 0xFF in SRAM where only the
ST/STS/STD and LD/LDS/LDD instructions can be used.

4.3

ALU – Arithmetic Logic Unit
The high-performance AVR ALU operates in direct connection with all the 32 general purpose
working registers. Within a single clock cycle, arithmetic operations between general purpose
registers or between a register and an immediate are executed. The ALU operations are divided
into three main categories – arithmetic, logical, and bit-functions. See the “Instruction Set” section for a detailed description.

4.4

Status Register
The Status Register contains information about the result of the most recently executed arithmetic instruction. This information can be used for altering program flow in order to perform

97707E–AVR–11/08

conditional operations. Note that the Status Register is updated after all ALU operations, as
specified in the Instruction Set Reference. This will in many cases remove the need for using thededicated compare instructions, resulting in faster and more compact code.
The Status Register is not automatically stored when entering an interrupt routine and restored
when returning from an interrupt. This must be handled by software.
The AVR Status Register – SREG – is defined as:
Bit

7

6

5

4

3

2

1

0

I

T

H

S

V

N

Z

C

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

SREG

• Bit 7 – I: Global Interrupt Enable
The Global Interrupt Enable bit must be set for the interrupts to be enabled. The individual interrupt enable control is then performed in separate control registers. If the Global Interrupt Enable
Register is cleared, none of the interrupts are enabled independent of the individual interrupt
enable settings. The I-bit is cleared by hardware after an interrupt has occurred, and is set by
the RETI instruction to enable subsequent interrupts. The I-bit can also be set and cleared by
the application with the SEI and CLI instructions, as described in the instruction set reference.
• Bit 6 – T: Bit Copy Storage
The Bit Copy instructions BLD (Bit LoaD) and BST (Bit STore) use the T-bit as source or destination for the operated bit. A bit from a register in the Register File can be copied into T by the
BST instruction, and a bit in T can be copied into a bit in a register in the Register File by the
BLD instruction.
• Bit 5 – H: Half Carry Flag
The Half Carry Flag H indicates a Half Carry in some arithmetic operations. Half Carry Is usefulin BCD arithmetic. See the “Instruction Set Description” for detailed information.
• Bit 4 – S: Sign Bit, S = N ⊕ V
The S-bit is always an exclusive or between the Negative Flag N and the Two’s Complement
Overflow Flag V. See the “Instruction Set Description” for detailed information.
• Bit 3 – V: Two’s Complement Overflow Flag
The Two’s Complement Overflow Flag V supports two’s complement arithmetics. See the“Instruction Set Description” for detailed information.
• Bit 2 – N: Negative Flag
The Negative Flag N indicates a negative result in an arithmetic or logic operation. See the“Instruction Set Description” for detailed information.
• Bit 1 – Z: Zero Flag
The Zero Flag Z indicates a zero result in an arithmetic or logic operation. See the “Instruction
Set Description” for detailed information.
• Bit 0 – C: Carry Flag
The Carry Flag C indicates a carry in an arithmetic or logic operation. See the “Instruction Set
Description” for detailed information.

10

AT90USB82/162

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AT90USB82/162
4.5

General Purpose Register FileThe Register File is optimized for the AVR Enhanced RISC instruction set. In order to achieve
the required performance and flexibility, the following input/output schemes are supported by theRegister File:• One 8-bit output operand and one 8-bit result input• Two 8-bit output operands and one 8-bit result input• Two 8-bit output operands and one 16-bit result input• One 16-bit output operand and one 16-bit result input
Figure 4-2 shows the structure of the 32 general purpose working registers in the CPU.
Figure 4-2.

AVR CPU General Purpose Working Registers
7

0

Addr.

R0

0x00

R1

0x01

R2

0x02

…
R13

0x0D

GeneralR14

0x0E

Purpose

R15

0x0F

Working

R16

0x10

Registers

R17

0x11

…
R26

0x1A

R27

0x1B

X-register Low Byte
X-register High Byte

R28

0x1C

Y-register Low Byte

R29

0x1D

Y-register High Byte

R30

0x1E

Z-register Low Byte

R31

0x1F

Z-register High Byte

Most of the instructions operating on the Register File have direct access to all registers, andmost of them are single cycle instructions.
As shown in Figure 4-2, each register is also assigned a data memory address, mapping them
directly into the first 32 locations of the user Data Space. Although not being physically implemented as SRAM locations, this memory organization provides great flexibility in access of theregisters, as the X-, Y- and Z-pointer registers can be set to index any register in the file.
4.5.1

The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These registers are 16-bit address pointers for indirect addressing of the data space. The three indirect
address registers X, Y, and Z are defined as described in Figure 4-3.
Figure 4-3.

The X-, Y-, and Z-registers
15

X-register

XH

7
R27 (0x1B)

15

XL
0

7

0
0

R26 (0x1A)

YH

YL

0

11
7707E–AVR–11/08

Y-register

70

R29 (0x1D)

Z-register

70

R28 (0x1C)

15

ZH

7

0

ZL
7

R31 (0x1F)

00R30 (0x1E)

In the different addressing modes these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).

4.6

Stack PointerThe Stack is mainly used for storing temporary data, for storing local variables and for storing
return addresses after interrupts and subroutine calls. The Stack Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory locations to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set topoint above 0x0100. The initial value of the stack pointer is the last address of the internal
SRAM. The Stack Pointer is decremented by one when data is pushed onto the Stack with the
PUSH instruction, and it is decremented by three when the return address is pushed onto the
Stack with subroutine call or interrupt. The Stack Pointer is incremented by one when data ispopped from the Stack with the POP instruction, and it is incremented by three when data ispopped from the Stack with return from subroutine RET or return from interrupt RETI.
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number ofbits actually used is implementation dependent. Note that the data space in some implementations of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
Bit

Read/Write
Initial Value

4.7

15

14

13

12

11

10

9

8

SP15

SP14

SP13

SP12

SP11

SP10

SP9

SP8

SPH

SP7

SP6

SP5

SP4

SP3

SP2

SP1

SP0

SPL

7

6

5

4

3

2

1

0

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

0

0

1

0

0

0

0

0

1

1

1

1

1

1

1

1

Instruction Execution TimingThis section describes the general access timing concepts for instruction execution. The AVR
CPU is driven by the CPU clock clkCPU, directly generated from the selected clock source for thechip. No internal clock division is used.
Figure 4-4 shows the parallel instruction fetches and instruction executions enabled by the Harvard architecture and the fast-access Register File concept. This is the basic pipelining concept
to obtain up to 1 MIPS per MHz with the corresponding unique results for functions per cost,functions per clocks, and functions per power-unit.

12

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
Figure 4-4.

The Parallel Instruction Fetches and Instruction Executions
T1

T2

T3

T4

clkCPU
1st Instruction Fetch
1st Instruction Execute
2nd Instruction Fetch
2nd Instruction Execute
3rd Instruction Fetch
3rd Instruction Execute
4th Instruction Fetch

Figure 4-5 shows the internal timing concept for the Register File. In a single clock cycle an ALU
operation using two register operands is executed, and the result is stored back to the destination register.
Figure 4-5.

Single Cycle ALU Operation
T1

T2

T3

T4

clkCPU
Total Execution Time
Register Operands Fetch
ALU Operation Execute
Result Write Back

4.8

Reset and Interrupt Handling
The AVR provides several different interrupt sources. These interrupts and the separate Reset
Vector each have a separate program vector in the program memory space. All interrupts are
assigned individual enable bits which must be written logic one together with the Global Interrupt
Enable bit in the Status Register in order to enable the interrupt. Depending on the Program
Counter value, interrupts may be automatically disabled when Boot Lock bits BLB02 or BLB12
are programmed. This feature improves software security. See the section “Memory Programming” on page 243 for details.
The lowest addresses in the program memory space are by default defined as the Reset andInterrupt Vectors. The complete list of vectors is shown in “Interrupts” on page 63. The list also
determines the priority levels of the different interrupts. The lower the address the higher is thepriority level. RESET has the highest priority, and next is INT0 – the External Interrupt Request
0. The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL
bit in the MCU Control Register (MCUCR). Refer to “Interrupts” on page 63 for more information.
The Reset Vector can also be moved to the start of the Boot Flash section by programming the
BOOTRST Fuse, see “Memory Programming” on page 243.
When an interrupt occurs, the Global Interrupt Enable I-bit is cleared and all interrupts are disabled. The user software can write logic one to the I-bit to enable nested interrupts. All enabledinterrupts can then interrupt the current interrupt routine. The I-bit is automatically set when a
Return from Interrupt instruction – RETI – is executed.
13

7707E–AVR–11/08

There are basically two types of interrupts. The first type is triggered by an event that sets theInterrupt Flag. For these interrupts, the Program Counter is vectored to the actual Interrupt Vector in order to execute the interrupt handling routine, and hardware clears the corresponding
Interrupt Flag. Interrupt Flags can also be cleared by writing a logic one to the flag bit position(s)to be cleared. If an interrupt condition occurs while the corresponding interrupt enable bit iscleared, the Interrupt Flag will be set and remembered until the interrupt is enabled, or the flag iscleared by software. Similarly, if one or more interrupt conditions occur while the Global Interrupt
Enable bit is cleared, the corresponding Interrupt Flag(s) will be set and remembered until the
Global Interrupt Enable bit is set, and will then be executed by order of priority.
The second type of interrupts will trigger as long as the interrupt condition is present. These
interrupts do not necessarily have Interrupt Flags. If the interrupt condition disappears before theinterrupt is enabled, the interrupt will not be triggered.
When the AVR exits from an interrupt, it will always return to the main program and execute one
more instruction before any pending interrupt is served.
Note that the Status Register is not automatically stored when entering an interrupt routine, nor
restored when returning from an interrupt routine. This must be handled by software.
When using the CLI instruction to disable interrupts, the interrupts will be immediately disabled.
No interrupt will be executed after the CLI instruction, even if it occurs simultaneously with the
CLI instruction. The following example shows how this can be used to avoid interrupts during thetimed EEPROM write sequence..
Assembly Code Example
in r16, SREGcli

; store SREG value; disable interrupts during timed sequencesbi EECR, EEMPE; start EEPROM write

sbi EECR, EEPE
out SREG, r16; restore SREG value (I-bit)

C Code Example
char cSREG;cSREG = SREG; /* store SREG value *//* disable interrupts during timed sequence */__disable_interrupt();
EECR |= (1<<EEMPE); /* start EEPROM write */EECR |= (1<<EEPE);
SREG = cSREG; /* restore SREG value (I-bit) */When using the SEI instruction to enable interrupts, the instruction following SEI will be executed before any pending interrupts, as shown in this example.

14

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AT90USB82/162
Assembly Code Examplesei; set Global Interrupt Enable

sleep; enter sleep, waiting for interrupt; note: will enter sleep before any pending; interrupt(s)C Code Example__enable_interrupt(); /* set Global Interrupt Enable */__sleep(); /* enter sleep, waiting for interrupt *//* note: will enter sleep before any pending interrupt(s) */4.8.1

Interrupt Response TimeThe interrupt execution response for all the enabled AVR interrupts is five clock cycles minimum.
After five clock cycles the program vector address for the actual interrupt handling routine is executed. During these five clock cycle period, the Program Counter is pushed onto the Stack. The
vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If aninterrupt occurs during execution of a multi-cycle instruction, this instruction is completed before
the interrupt is served. If an interrupt occurs when the MCU is in sleep mode, the interrupt execution response time is increased by five clock cycles. This increase comes in addition to thestart-up time from the selected sleep mode.
A return from an interrupt handling routine takes three clock cycles. During these three clock
cycles, the Program Counter (three bytes) is popped back from the Stack, the Stack Pointer isincremented by three, and the I-bit in SREG is set.

15
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5. AVR AT90USB82/162 Memories
This section describes the different memories in the AT90USB82/162. The AVR architecture has
two main memory spaces, the Data Memory and the Program Memory space. In addition, theAT90USB82/162 features an EEPROM Memory for data storage. All three memory spaces arelinear and regular.

5.1

In-System Reprogrammable Flash Program Memory
The AT90USB82/162 contains 8K / 16K bytes On-chip In-System Reprogrammable Flash memory for program storage. Since all AVR instructions are 16 or 32 bits wide, the Flash is organized
as 4K x 16, 8K x 16. For software security, the Flash Program memory space is divided into two
sections, Boot Program section and Application Program section.
The Flash memory has an endurance of at least 100,000 write/erase cycles. The
AT90USB82/162 Program Counter (PC) is 16 bits wide, thus addressing the 8K / 16K program
memory locations. The operation of Boot Program section and associated Boot Lock bits forsoftware protection are described in detail in “Memory Programming” on page 243. “Memory
Programming” on page 243 contains a detailed description on Flash data serial downloading
using the SPI pins or the debugWIRE interface.
Constant tables can be allocated within the entire program memory address space (see the LPM– Load Program Memory instruction description and ELPM - Extended Load Program Memory
instruction description).
Timing diagrams for instruction fetch and execution are presented in “Instruction Execution Timing” on page 12.

16

AT90USB82/162

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AT90USB82/162
Figure 5-1.

Program Memory Map

Program Memory
0x00000

Application Flash Section

Boot Flash Section
0x3FFF (16KBytes)
0x1FFF (8KBytes)

5.2

SRAM Data Memory
Figure 5-2 shows how the AT90USB82/162 SRAM Memory is organized.
The AT90USB82/162 is a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in the Opcode for the IN and OUT instructions. For the
Extended I/O space from $060 - $0FF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
The first 768 Data Memory locations address the Register File, the I/O Memory, Extended I/OMemory, and the internal data SRAM. The first 32 locations address the Register file, the next
64 location the standard I/O Memory, then 160 locations of Extended I/O memory, and the 512
locations of internal data SRAM.The five different addressing modes for the data memory cover:Direct, Indirect with Displacement, Indirect, Indirect with Pre-decrement, and Indirect with Postincrement. In the Register file, registers R26 to R31 feature the indirect addressing pointerregisters.
The direct addressing reaches the entire data space.
The Indirect with Displacement mode reaches 63 address locations from the base address givenby the Y- or Z-register.
When using register indirect addressing modes with automatic pre-decrement and post-increment, the address registers X, Y, and Z are decremented or incremented.

177707E–AVR–11/08

The 32 general purpose working registers, 64 I/O registers, and the 512 bytes of internal data
SRAM in the AT90USB82/162 are all accessible through all these addressing modes. The Register File is described in “General Purpose Register File” on page 11.
Figure 5-2.

Data Memory Map

Data Memory
32 Registers
64 I/O Registers
160 E xt I/O Reg.

$0000 - $001F$0020 - $005F$0060 - $00FF$0100

Internal S RAM(512 x 8)
$2FF

5.2.1

Data Memory Access Times
This section describes the general access timing concepts for internal memory access. Theinternal data SRAM access is performed in two clkCPU cycles as described in Figure 5-3.
Figure 5-3.

On-chip Data SRAM Access Cycles
T1

T2

Compute Address

Address valid

T3

clkCPU
Address

Write

Data
WR

Read

Data
RD

Memory Access Instruction

5.3

Next Instruction

EEPROM Data Memory
The AT90USB82/162 contains 512 bytes of data EEPROM memory. It is organized as a separate data space, in which single bytes can be read and written. The EEPROM has an enduranceof at least 100,000 write/erase cycles. The access between the EEPROM and the CPU isdescribed in the following, specifying the EEPROM Address Registers, the EEPROM Data Register, and the EEPROM Control Register.

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AT90USB82/162
For a detailed description of SPI, debugWIRE and Parallel data downloading to the EEPROM,
see page 257, page 241, and page 246 respectively.
5.3.1

EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 5-2. A self-timing function, however,lets the user software detect when the next byte can be written. If the user code contains instructions that write the EEPROM, some precautions must be taken. In heavily filtered power
supplies, VCC is likely to rise or fall slowly on power-up/down. This causes the device for someperiod of time to run at a voltage lower than specified as minimum for the clock frequency used.
See “Preventing EEPROM Corruption” on page 23. for details on how to avoid problems in thesesituations.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to the description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.

5.3.2

The EEPROM Address Register – EEARH and EEARL
Bit

Read/Write
Initial Value

15

14

13

12

11

10

9

8

–

–

–

–

EEAR11

EEAR10

EEAR9

EEAR8

EEARH

EEAR7

EEAR6

EEAR5

EEAR4

EEAR3

EEAR2

EEAR1

EEAR0

EEARL

7

6

5

4

3

2

1

0

R

R

R

R

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

0

0

0

0

X

X

X

X

X

X

X

X

X

X

X

X

• Bits 15..12 – Res: Reserved Bits
These bits are reserved bits in the AT90USB82/162 and will always read as zero.
• Bits 11..0 – EEAR8..0: EEPROM Address
The EEPROM Address Registers – EEARH and EEARL specify the EEPROM address in the
512 bytes EEPROM space. The EEPROM data bytes are addressed linearly between 0 and
512. The initial value of EEAR is undefined. A proper value must be written before the EEPROM
may be accessed.
5.3.3

The EEPROM Data Register – EEDR
Bit

7

6

5

4

3

2

1

0

MSB

LSB

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

EEDR

• Bits 7..0 – EEDR7.0: EEPROM Data
For the EEPROM write operation, the EEDR Register contains the data to be written to the
EEPROM in the address given by the EEAR Register. For the EEPROM read operation, theEEDR contains the data read out from the EEPROM at the address given by EEAR.

197707E–AVR–11/08

5.3.4The EEPROM Control Register – EECR
Bit

7

6

5

4

3

2

1

–

–

EEPM1

EEPM0

EERIE

EEMPE

EEPE

0
EERE

Read/Write

R

R

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

X

X

0

0

X

0

EECR

• Bits 7..6 – Res: Reserved Bits
These bits are reserved bits in the AT90USB82/162 and will always read as zero.
• Bits 5, 4 – EEPM1 and EEPM0: EEPROM Programming Mode Bits
The EEPROM Programming mode bit setting defines which programming action that will be triggered when writing EEPE. It is possible to program data in one atomic operation (erase the oldvalue and program the new value) or to split the Erase and Write operations in two different
operations. The Programming times for the different modes are shown in Table 5-1. While EEPE
is set, any write to EEPMn will be ignored. During reset, the EEPMn bits will be reset to 0b00
unless the EEPROM is busy programming.

Table 5-1.

EEPROM Mode Bits

EEPM1

EEPM0

Programming
Time

0

0

3.4 msErase and Write in one operation (Atomic Operation)

01

1.8 msErase Only

10

1.8 msWrite Only

1

1

–

Operation

Reserved for future use• Bit 3 – EERIE: EEPROM Ready Interrupt Enable
Writing EERIE to one enables the EEPROM Ready Interrupt if the I bit in SREG is set. Writing
EERIE to zero disables the interrupt. The EEPROM Ready interrupt generates a constant interrupt when EEPE is cleared.
• Bit 2 – EEMPE: EEPROM Master Programming Enable
The EEMPE bit determines whether setting EEPE to one causes the EEPROM to be written.
When EEMPE is set, setting EEPE within four clock cycles will write data to the EEPROM at the
selected address If EEMPE is zero, setting EEPE will have no effect. When EEMPE has been
written to one by software, hardware clears the bit to zero after four clock cycles. See thedescription of the EEPE bit for an EEPROM write procedure.
• Bit 1 – EEPE: EEPROM Programming Enable
The EEPROM Write Enable Signal EEPE is the write strobe to the EEPROM. When addressand data are correctly set up, the EEPE bit must be written to one to write the value into the
EEPROM. The EEMPE bit must be written to one before a logical one is written to EEPE, otherwise no EEPROM write takes place. The following procedure should be followed when writing
the EEPROM (the order of steps 3 and 4 is not essential):
1. Wait until EEPE becomes zero.
2. Wait until SELFPRGEN in SPMCSR becomes zero.
3. Write new EEPROM address to EEAR (optional).

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AT90USB82/162
4. Write new EEPROM data to EEDR (optional).
5. Write a logical one to the EEMPE bit while writing a zero to EEPE in EECR.
6. Within four clock cycles after setting EEMPE, write a logical one to EEPE.
The EEPROM can not be programmed during a CPU write to the Flash memory. The softwaremust check that the Flash programming is completed before initiating a new EEPROM write.
Step 2 is only relevant if the software contains a Boot Loader allowing the CPU to program theFlash. If the Flash is never being updated by the CPU, step 2 can be omitted. See “Memory Programming” on page 243 for details about Boot programming.
Caution: An interrupt between step 5 and step 6 will make the write cycle fail, since the
EEPROM Master Write Enable will time-out. If an interrupt routine accessing the EEPROM isinterrupting another EEPROM access, the EEAR or EEDR Register will be modified, causing theinterrupted EEPROM access to fail. It is recommended to have the Global Interrupt Flag cleared
during all the steps to avoid these problems.
When the write access time has elapsed, the EEPE bit is cleared by hardware. The user software can poll this bit and wait for a zero before writing the next byte. When EEPE has been set,
the CPU is halted for two cycles before the next instruction is executed.
• Bit 0 – EERE: EEPROM Read Enable
The EEPROM Read Enable Signal EERE is the read strobe to the EEPROM. When the correct
address is set up in the EEAR Register, the EERE bit must be written to a logic one to trigger the
EEPROM read. The EEPROM read access takes one instruction, and the requested data isavailable immediately. When the EEPROM is read, the CPU is halted for four cycles before thenext instruction is executed.
The user should poll the EEPE bit before starting the read operation. If a write operation is inprogress, it is neither possible to read the EEPROM, nor to change the EEAR Register.
The calibrated Oscillator is used to time the EEPROM accesses. Table 5-2 lists the typical programming time for EEPROM access from the CPU.
Table 5-2.

EEPROM Programming Time

SymbolEEPROM write(from CPU)

Number of Calibrated RC Oscillator Cycles

Typ Programming Time

26,368

3.3 ms

The following code examples show one assembly and one C function for writing to the
EEPROM. The examples assume that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these functions. The examples also

217707E–AVR–11/08

assume that no Flash Boot Loader is present in the software. If such code is present, the
EEPROM write function must also wait for any ongoing SPM command to finish.
Assembly Code Example(1)EEPROM_write:; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_write; Set up address (r18:r17) in address registerout EEARH, r18
out EEARL, r17; Write data (r16) to Data Registerout EEDR,r16; Write logical one to EEMPE
sbi EECR,EEMPE; Start eeprom write by setting EEPE
sbi EECR,EEPE
ret

C Code Example(1)void EEPROM_write(unsigned int uiAddress, unsigned char ucData){/* Wait for completion of previous write */while(EECR & (1<<EEPE));/* Set up address and Data Registers */EEAR = uiAddress;
EEDR = ucData;/* Write logical one to EEMPE */EECR |= (1<<EEMPE);/* Start eeprom write by setting EEPE */EECR |= (1<<EEPE);
}
Note:

22

1. See “About Code Examples” on page 7.

AT90USB82/162

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AT90USB82/162
The next code examples show assembly and C functions for reading the EEPROM. The examples assume that interrupts are controlled so that no interrupts will occur during execution ofthese functions.
Assembly Code Example(1)EEPROM_read:; Wait for completion of previous write
sbic EECR,EEPE
rjmp EEPROM_read; Set up address (r18:r17) in address registerout EEARH, r18
out EEARL, r17; Start eeprom read by writing EERE
sbi EECR,EERE; Read data from Data Registerinr16,EEDR

ret

C Code Example(1)unsigned char EEPROM_read(unsigned int uiAddress){/* Wait for completion of previous write */while(EECR & (1<<EEPE));/* Set up address register */EEAR = uiAddress;/* Start eeprom read by writing EERE */EECR |= (1<<EERE);/* Return data from Data Register */return EEDR;
}
Note:

5.3.5

1. See “About Code Examples” on page 7.

Preventing EEPROM Corruption
During periods of low VCC, the EEPROM data can be corrupted because the supply voltage is
too low for the CPU and the EEPROM to operate properly. These issues are the same as forboard level systems using EEPROM, and the same design solutions should be applied.
An EEPROM data corruption can be caused by two situations when the voltage is too low. First,
a regular write sequence to the EEPROM requires a minimum voltage to operate correctly. Secondly, the CPU itself can execute instructions incorrectly, if the supply voltage is too low.
EEPROM data corruption can easily be avoided by following this design recommendation:
Keep the AVR RESET active (low) during periods of insufficient power supply voltage. This canbe done by enabling the internal Brown-out Detector (BOD). If the detection level of the internal
BOD does not match the needed detection level, an external low VCC reset Protection circuit can

237707E–AVR–11/08

be used. If a reset occurs while a write operation is in progress, the write operation will be completed provided that the power supply voltage is sufficient.

5.4

I/O Memory
The I/O space definition of the AT90USB82/162 is shown in “Register Summary” on page 288.
All AT90USB82/162 I/Os and peripherals are placed in the I/O space. All I/O locations may beaccessed by the LD/LDS/LDD and ST/STS/STD instructions, transferring data between the 32
general purpose working registers and the I/O space. I/O Registers within the address range
0x00 - 0x1F are directly bit-accessible using the SBI and CBI instructions. In these registers, thevalue of single bits can be checked by using the SBIS and SBIC instructions. Refer to the
instruction set section for more details. When using the I/O specific commands IN and OUT, theI/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using
LD and ST instructions, 0x20 must be added to these addresses. The AT90USB82/162 is acomplex microcontroller with more peripheral units than can be supported within the 64 location
reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 0x1FF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.
For compatibility with future devices, reserved bits should be written to zero if accessed.
Reserved I/O memory addresses should never be written.
Some of the Status Flags are cleared by writing a logical one to them. Note that, unlike mostother AVRs, the CBI and SBI instructions will only operate on the specified bit, and can therefore
be used on registers containing such Status Flags. The CBI and SBI instructions work with registers 0x00 to 0x1F only.
The I/O and peripherals control registers are explained in later sections.

5.4.1

General Purpose I/O Registers
The AT90USB82/162 contains three General Purpose I/O Registers. These registers can beused for storing any information, and they are particularly useful for storing global variables andStatus Flags. General Purpose I/O Registers within the address range 0x00 - 0x1F are directly
bit-accessible using the SBI, CBI, SBIS, and SBIC instructions.

5.4.2

General Purpose I/O Register 2 – GPIOR2
Bit

7

6

5

4

3

2

1

0

MSB

5.4.3

LSB

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

5

4

3

2

1

General Purpose I/O Register 1 – GPIOR1
Bit

7

6

MSB

5.4.4

0
LSB

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

6

5

4

3

2

1

0

GPIOR1

General Purpose I/O Register 0 – GPIOR0
Bit

7
MSB

24

GPIOR2

LSB

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

AT90USB82/162

GPIOR07707E–AVR–11/08

AT90USB82/162
6. System Clock and Clock Options
6.1

Clock Systems and their Distribution
Figure 6-1 presents the principal clock systems in the AVR and their distribution. All of the clocks
need not be active at a given time. In order to reduce power consumption, the clocks to modules
not being used can be halted by using different sleep modes, as described in “Power Management and Sleep Modes” on page 41. The clock systems are detailed below.
Figure 6-1.

Clock DistributionUSB

clkUSB (48MHz)

General I/O
Modules

clkI/OCPU Core

AVR ClockControl Unit

RAM

Flash and
EEPROM

clkCPU
clkFLASH

USB PLL
X6

Reset Logic

clkPllin (8MHz)
PLL Clock
Prescaler

Source clock

Watchdog Timer

Watchdog clock

System Clock
Prescaler

clkXTAL (2-16 MHz)

Clock
Multiplexer
Clock
SwitchCrystalOscillator

External Clock

Watchdog
Oscillator

Calibrated RC
Oscillator

6.1.1

CPU Clock – clkCPU
The CPU clock is routed to parts of the system concerned with operation of the AVR core.
Examples of such modules are the General Purpose Register File, the Status Register and thedata memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.

6.1.2

I/O Clock – clkI/O
The I/O clock is used by the majority of the I/O modules, like Timer/Counters, SPI, and USART.
The I/O clock is also used by the External Interrupt module, but note that some external interrupts are detected by asynchronous logic, allowing such interrupts to be detected even if the I/Oclock is halted.

6.1.3

Flash Clock – clkFLASHThe Flash clock controls operation of the Flash interface. The Flash clock is usually active simultaneously with the CPU clock.

25
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6.1.4

6.2

USB Clock – clkUSB
The USB is provided with a dedicated clock domain. This clock is generated with an on-chip PLL
running at 48MHz. The PLL always multiply its input frequency by 6. Thus the PLL clock registershould be programmed by software to generate a 8MHz clock on the PLL input.

Clock Switch
In the AT90USB82/162 product, the Clock Multiplexer and the System Clock Prescaler can be
modified by software.

6.2.1

Exemple of use
The modification can occur when the device enters in USB Suspend mode. It then switches from
External Clock to Calibrated RC Oscillator in order to reduce consumption. In such a configuration, the External Clock is disabled.
The firmware can use the watchdog timer to be woken-up from power-down in order to check if
there is an event on the application.
If an event occurs on the application or if the USB controller signals a non-idle state on the USB
line (Resume for example), the firmware switches the Clock Multiplexer from the Calibrated RC
Oscillator to the External Clock.
Figure 6-2.

Example of clock switching with wake-up from USB Host
resume1 Resume from HostUSB

non-Idle

CPU Clock

Idle
Ext

non-Idle(Suspend)

RC

1

Ext

External
Oscillator
RC oscillator
3ms

26

AT90USB82/162

watchdog wake-up
from power-down

7707E–AVR–11/08

AT90USB82/162
Figure 6-3.

Example of clock switching with wake-up from Device
upstream-resume
2 Upstream Resume from deviceUSB

non-Idle

Idle

CPU Clocknon-Idle(Suspend)

Ext

2

RC

Ext

External
Oscillator
RC oscillator
3ms
6.2.2
6.2.2.1

watchdog wake-up
from power-down

Clock switch Algorythm
Swith from external clock to RC clock
if (Usb_suspend_detected())// if (UDINT.SUSPI == 1){
Usb_ack_suspend();// UDINT.SUSPI = 0;

Usb_freeze_clock();// USBCON.FRZCLK = 1;

Disable_pll();// PLLCSR.PLLE = 0;

Enable_RC_clock();// CLKSEL0.RCE = 1;

while (!RC_clock_ready());// while (CLKSTA.RCON != 1);

Select_RC_clock();// CLKSEL0.CLKS = 0;

Disable_external_clock();// CLKSEL0.EXTE = 0;}

6.2.2.2

Switch from RC clock to external clock
if (Usb_wake_up_detected())// if (UDINT.WAKEUPI == 1){
Usb_ack_wake_up();// UDINT.WAKEUPI = 0;

Enable_external_clock();// CLKSEL0.EXTE = 1;

while (!External_clock_ready()); // while (CLKSTA.EXTON != 1);
Select_external_clock();// CLKSEL0.CLKS = 1;

Enable_pll();// PLLCSR.PLLE = 1;

Disable_RC_clock();// CLKSEL0.RCE = 0;

while (!Pll_ready());// while (PLLCSR.PLOCK != 1);

Usb_unfreeze_clock();// USBCON.FRZCLK = 0;

}

6.2.3

Clock Selection Register 0 – CLKSEL0
Bit

7

6

5

4

3

2

1

RCSUT1

RCSUT0

EXSUT1

EXSUT0

RCE

EXTE

-

0
CLKS

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R

R/W

Initial Value

0

0

0

0

See Bit Description

CLKSEL0277707E–AVR–11/08

• Bit 7-6 – RCSUT[1:0]: SUT for RC oscillator
These 2 bits are the SUT value for the RC Oscillator. If the RC oscillator is selected by fuse bits,
the SUT fuse are copied into these bits. A firmware change will not have any effect because thisadditionnal start-up time is only used after a reset and not after a clock switch.
• Bit 5-4 – EXSUT[1:0]: SUT for External Oscillator / Low Power Oscillator
These 2 bits are the SUT value for the External Oscillator / Low Power Oscillator. If the External
oscillator / Low Power Oscillator is selected by fuse bits, the SUT fuse are copyed into thesebits. The firmware can modify these bits by writing a new value. This value will be used at thenext start of the External Oscillator / Low Power Oscillator.
• Bit 3 – RCE: Enable RC Oscillator
The RCE bit must be written to logic one to enable the RC Oscillator. The RCE bit must be written to logic zero to disable the RC Oscillator.
• Bit 2 – EXTE: Enable External Oscillator / Low Power Oscillator
The OSCE bit must be written to logic one to enable External Oscillator / Low Power Oscillator.
The OSCE bit must be written to logic zero to disable the External Oscillator / Low Power
Oscillator.
• Bit 0 – CLKS: Clock Selector
The CLKS bit must be written to logic one to select the External Oscillator / Low Power Oscillator
as CPU clock. The CLKS bit must be written to logic zero to select the RC Oscillator as CPU
clock. After a reset, the CLKS bit is set by hardware if the External Oscillator / Low Power Oscillator is selected by the fuse bits configuration.
The firmware has to check if the clock is correctly started before selected it.
6.2.4

Clock Selection Register 1 – CLKSEL1
Bit

7

6

5

4

3

2

1

0

RCCKSE
L3

RCCKS
EL2

RCCLK
SEL1

RCCLK
SEL0

EXCKSE
L3

EXCKSEL2

EXCLKSEL1EXCLKS
EL0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

1

0

0

0

0

0

CLKSEL1• Bit 7-4 – RCCKSEL[3:0]: CKSEL for RC oscillator
Clock configuration for the RC Oscillator. After a reset, this part of the register is loaded with the0010b value that corresponds to the RC oscillator. Modifying this value by firmware before
switching to RC oscillator is prohibited because the RC clock will not start.
• Bit 3-0 – EXCKSEL[3:0]: CKSEL for External oscillator / Low Power Oscillator
Clock configuration for the External Oscillator / Low Power Oscillator. After a reset, if the External oscillator / Low Power Oscillator is selected by fuse bits, this part of the register is loadedwith the fuse configuration. Firmware can modify it to change the start-up time after the clock
switch.

28

AT90USB82/162

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AT90USB82/162
6.2.5

Clock Status Register – CLKSTA
Bit

7

6

5

4

3

2

1

-

-

-

-

-

-

RCON

0
EXTON

Read/Write

R

R

R

R

R

R

R

R

Initial Value

0

0

0

0

See Bit Description

CLKSTA• Bit 7-2 - Reserved bits
These bits are reserved and will always read as zero.
• Bit 1 – RCON: RC Oscillator On
This bit is set by hardware to one if the RC Oscillator is running.
This bit is set by hardware to zero if the RC Oscillator is stoped.
• Bit 0 – EXTON: External Oscillator / Low Power Oscillator On
This bit is set by hardware to one if the External Oscillator / Low Power Oscillator is running.
This bit is set by hardware to zero if the External Oscillator / Low Power Oscillator is stoped.

6.3

Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits as shown
below. The clock from the selected source is input to the AVR clock generator, and routed to theappropriate modules.
Table 6-1.

Device Clocking Options Select(1)Device Clocking Option

CKSEL3..0

Low Power Crystal Oscillator

1111 - 1000

Reserved

0111 - 0110

Reserved

0101 - 0100

Reserved

0011

Calibrated Internal RC Oscillator

0010

External Clock

0000

Reserved

0001

Note:

1. For all fuses “1” means unprogrammed while “0” means programmed.

6.3.1

Default Clock Source
The device is shipped with low power crystal oscillator and with the fuse CKDIV8 programmed.
The startup time is set to maximum and time-out period enabled. (CKSEL = "1110", SUT = "01",CKDIV8 = "0").

6.3.2

Clock Startup Sequence
Any clock source needs a sufficient VCC to start oscillating and a minimum number of oscillating
cycles before it can be considered stable.
To ensure sufficient VCC, the device issues an internal reset with a time-out delay (tTOUT) after
the device reset is released by all other reset sources. “On-chip Debug System” on page 45
describes the start conditions for the internal reset. The delay (tTOUT) is timed from the Watchdog
Oscillator and the number of cycles in the delay is set by the SUTx and CKSELx fuse bits. The
selectable delays are shown in Table 6-2. The frequency of the Watchdog Oscillator is voltage

297707E–AVR–11/08

dependent as shown in “AT90USB82/162 Typical Characteristics – Preliminary Data” on page
268.
Table 6-2.

Number of Watchdog Oscillator Cycles

Typ Time-out (VCC = 5.0V)

Typ Time-out (VCC = 3.0V)

Number of Cycles

0 ms

0 ms

0

4.1 ms

4.3 ms

512

65 ms

69 ms

8K (8,192)

Main purpose of the delay is to keep the AVR in reset until it is supplied with minimum Vcc. The
delay will not monitor the actual voltage and it will be required to select a delay longer than the
Vcc rise time. If this is not possible, an internal or external Brown-Out Detection circuit should be
used. A BOD circuit will ensure sufficient Vcc before it releases the reset, and the time-out delay
can be disabled. Disabling the time-out delay without utilizing a Brown-Out Detection circuit is
not recommended.
The oscillator is required to oscillate for a minimum number of cycles before the clock is considered stable. An internal ripple counter monitors the oscillator output clock, and keeps the internal
reset active for a given number of clock cycles. The reset is then released and the device will
start to execute. The recommended oscillator start-up time is dependent on the clock type, andvaries from 6 cycles for an externally applied clock to 32K cycles for a low frequency crystal.
The start-up sequence for the clock includes both the time-out delay and the start-up time when
the device starts up from reset. When starting up from Power-save or Power-down mode, Vcc is
assumed to be at a sufficient level and only the start-up time is included.

6.4

Low Power Crystal Oscillator
Pins XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier which can be
configured for use as an On-chip Oscillator, as shown in Figure 6-4. Either a quartz crystal or aceramic resonator may be used.
This Crystal Oscillator is a low power oscillator, with reduced voltage swing on the XTAL2 output. It gives the lowest power consumption, but is not capable of driving other clock inputs, andmay be more susceptible to noise in noisy environments.
C1 and C2 should always be equal for both crystals and resonators. The optimal value of thecapacitors depends on the crystal or resonator in use, the amount of stray capacitance, and theelectromagnetic noise of the environment. Some initial guidelines for choosing capacitors foruse with crystals are given in Table 6-3. For ceramic resonators, the capacitor values given by
the manufacturer should be used.

30

AT90USB82/162

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AT90USB82/162
Figure 6-4.

Crystal Oscillator Connections

C2

XTAL2

C1

XTAL1
GND

The Low Power Oscillator can operate in three different modes, each optimized for a specific frequency range. The operating mode is selected by the fuses CKSEL3..1 as shown in Table 6-3.
Table 6-3.

Notes:

Low Power Crystal Oscillator Operating Modes(3)Frequency Range(1) (MHz)CKSEL3..1

Recommended Range for Capacitors C1
and C2 (pF)

0.4 - 0.9100(2)–

0.9 - 3.0

101

12 - 22

3.0 - 8.0

110

12 - 228.0 - 16.0

111

12 - 22

1. The frequency ranges are preliminary values. Actual values are TBD.
2. This option should not be used with crystals, only with ceramic resonators.
3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8. It must be ensured
that the resulting divided clock meets the frequency specification of the device.

The CLKSEL0 Fuse together with the SUT1..0 Fuses select the start-up times as shown in
Table 6-4.

Table 6-4.

Start-up Times for the Low Power Crystal Oscillator Clock Selection
Start-up Time fromPower-down andPower-save

Additional Delayfrom Reset(VCC = 5.0V)

CLKSEL0

SUT1..0

Ceramic resonator, fastrising power

258 CK

14CK + 4.1 ms(1)000

Ceramic resonator, slowly
rising power

258 CK

14CK + 65 ms(1)001Ceramic resonator, BOD
enabled

1K CK

14CK(2)0

10Ceramic resonator, fastrising power

1K CK

14CK + 4.1 ms(2)011Ceramic resonator, slowly
rising power

1K CK

14CK + 65 ms(2)100

Oscillator Source /Power Conditions

31
7707E–AVR–11/08

Table 6-4.

Start-up Times for the Low Power Crystal Oscillator Clock Selection (Continued)
Start-up Time fromPower-down andPower-save

Additional Delayfrom Reset(VCC = 5.0V)

CLKSEL0

SUT1..0

Crystal Oscillator, BOD
enabled

16K CK

14CK

1

01

Crystal Oscillator, fastrising power

16K CK

14CK + 4.1 ms

1

10

Crystal Oscillator, slowly
rising power

16K CK

14CK + 65 ms

1

11

Oscillator Source /Power Conditions

Notes:

1. These options should only be used when not operating close to the maximum frequency of thedevice, and only if frequency stability at start-up is not important for the application. These
options are not suitable for crystals.
2. These options are intended for use with ceramic resonators and will ensure frequency stability
at start-up. They can also be used with crystals when not operating close to the maximum frequency of the device, and if frequency stability at start-up is not important for the application.

Table 6-5.

Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Time from Powerdown and Power-save

Additional Delay from
Reset (VCC = 5.0V)

SUT1..0

BOD enabled

6 CK

14CK

00

Fast rising power

6 CK

14CK + 4.1 ms

01

6 CK

(1)

10

Power Conditions

Slowly rising power

14CK + 65 ms

Reserved
Note:

6.5

11

1. The device is shipped with this option selected.

Calibrated Internal RC Oscillator

The calibrated internal RC Oscillator by default provides a 8.0 MHz clock. The frequency is nominal value at 3.0V and 25°C. At 3.0V and 25°C, this calibration gives afrequency of 8 MHz ± 10%. The device is shipped with the CKDIV8 Fuse programmed.
See “System Clock Prescaler” on page 34 for more details. This clock may be selected
as the system clock by programming the CKSEL Fuses as shown in Table 6-6. If
selected, it will operate with no external components. During reset, hardware loads thecalibration byte into the OSCCAL Register and thereby automatically calibrates the RC
Oscillator. At 3.3V and 25⋅C, this calibration gives a frequency of 8 MHz ± 1%. The
oscillator can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ±1%
accuracy, by changing the OSCCAL register. When this Oscillator is used as the chipclock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the
Reset Time-out. For more information on the pre-programmed calibration value, see thesection “Calibration Byte” on page 246
Table 6-6.

Notes:

Internal Calibrated RC Oscillator Operating Modes(1)(3)Frequency Range(2) (MHz)CKSEL3..0

7.3 - 8.10010

1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values. Actual values are TBD.

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AT90USB82/162
3. If 8 MHz frequency exceeds the specification of the device (depends on VCC), the CKDIV8
Fuse can be programmed in order to divide the internal frequency by 8.

When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-5 on page 32.
Table 6-7.

Start-up times for the internal calibrated RC Oscillator clock selection
Start-up Time from Powerdown and Power-save

Additional Delay from
Reset (VCC = 5.0V)

SUT1..0

BOD enabled

6 CK

14 CK

00

Fast rising power

6 CK

14 CK + 4.1 ms

01

6 CK

(1)

10

Power Conditions

Slowly rising power

14 CK + 65 ms

Reserved
Note:

6.5.1

11

1. The device is shipped with this option selected.

Oscillator Calibration Register – OSCCAL
Bit

7

6

5

4

3

2

1

0

CAL7

CAL6

CAL5

CAL4

CAL3

CAL2

CAL1

CAL0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

Device Specific Calibration Value

OSCCAL• Bits 7..0 – CAL7..0: Oscillator Calibration ValueThe Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. The factory-calibrated value is automatically written to this register during chip reset, giving an oscillator frequency of 8.0 MHz at 25°C.
The application software can write this register to change the oscillator frequency. The oscillator
can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ±1% accuracy. Calibration
outside that range is not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to morethan 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives thelowest frequency range, setting this bit to 1 gives the highest frequency range. The two frequency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher
frequency than OSCCAL = 0x80.
The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00
gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in therange. Incrementing CAL6..0 by 1 will give a frequency increment of less than 2% in the frequency range 7.3 - 8.1 MHz.

33
7707E–AVR–11/08

6.6

External Clock
The device can utilize a external clock source as shown in Figure 6-5. To run the device on an
external clock, the CKSEL Fuses must be programmed as shown in Table 6-1.
Figure 6-5.

External Clock Drive Configuration

NC

XTAL2

EXTERNAL
CLOCK
SIGNALXTAL1

GNDWhen this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table 6-8.
Table 6-8.

Start-up Times for the External Clock Selection
Start-up Time from Powerdown and Power-save

Additional Delay from
Reset (VCC = 5.0V)

SUT1..0

BOD enabled

6 CK

14CK

00

Fast rising power

6 CK

14CK + 4.1 ms

01

Slowly rising power

6 CK

14CK + 65 ms

10Power Conditions

Reserved

11

When applying an external clock, it is required to avoid sudden changes in the applied clock frequency to ensure stable operation of the MCU. A variation in frequency of more than 2% fromone clock cycle to the next can lead to unpredictable behavior. If changes of more than 2% isrequired, ensure that the MCU is kept in Reset during the changes.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to “System Clock Prescaler” on page
34 for details.

6.7

Clock Output Buffer
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT
Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other circuits on the system. The clock also will be output during reset, and the normal operation of I/O
pin will be overridden when the fuse is programmed. Any clock source, including the internal RC
Oscillator, can be selected when the clock is output on CLKO. If the System Clock Prescaler isused, it is the divided system clock that is output.

6.8

System Clock Prescaler
The AT90USB82/162 has a system clock prescaler, and the system clock can be divided by setting the “Clock Prescale Register – CLKPR” on page 35. This feature can be used to decrease

34

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AT90USB82/162
the system clock frequency and the power consumption when the requirement for processing
power is low. This can be used with all clock source options, and it will affect the clock frequencyof the CPU and all synchronous peripherals. clkI/O, clkCPU, and clkFLASH are divided by a factor as
shown in Table 6-9.
When switching between prescaler settings, the System Clock Prescaler ensures that noglitches occurs in the clock system. It also ensures that no intermediate frequency is higher thanneither the clock frequency corresponding to the previous setting, nor the clock frequency corresponding to the new setting.
The ripple counter that implements the prescaler runs at the frequency of the undivided clock,which may be faster than the CPU's clock frequency. Hence, it is not possible to determine thestate of the prescaler - even if it were readable, and the exact time it takes to switch from one
clock division to the other cannot be exactly predicted. From the time the CLKPS values are written, it takes between T1 + T2 and T1 + 2 * T2 before the new clock frequency is active. In thisinterval, 2 active clock edges are produced. Here, T1 is the previous clock period, and T2 is theperiod corresponding to the new prescaler setting.
To avoid unintentional changes of clock frequency, a special write procedure must be followed
to change the CLKPS bits:
1. Write the Clock Prescaler Change Enable (CLKPCE) bit to one and all other bits in
CLKPR to zero.
2. Within four cycles, write the desired value to CLKPS while writing a zero to CLKPCE.
Interrupts must be disabled when changing prescaler setting to make sure the write procedure is
not interrupted.
6.8.1

Clock Prescale Register – CLKPR
Bit

7

6

5

4

3

2

1

CLKPCE–––CLKPS3

CLKPS2

CLKPS10
CLKPS0

Read/Write

R/W

R

R

R

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

See Bit Description

CLKPR• Bit 7 – CLKPCE: Clock Prescaler Change Enable
The CLKPCE bit must be written to logic one to enable change of the CLKPS bits. The CLKPCE
bit is only updated when the other bits in CLKPR are simultaneously written to zero. CLKPCE iscleared by hardware four cycles after it is written or when CLKPS bits are written. Rewriting the
CLKPCE bit within this time-out period does neither extend the time-out period, nor clear the
CLKPCE bit.
• Bit 6-4 - Reserved bits
These bits are reserved and will always read as zero.
• Bits 3..0 – CLKPS3..0: Clock Prescaler Select Bits 3 - 0
These bits define the division factor between the selected clock source and the internal system
clock. These bits can be written run-time to vary the clock frequency to suit the application
requirements. As the divider divides the master clock input to the MCU, the speed of all synchronous peripherals is reduced when a division factor is used. The division factors are given in
Table 6-9.
The CKDIV8 Fuse determines the initial value of the CLKPS bits. If CKDIV8 is unprogrammed,
the CLKPS bits will be reset to “0000”. If CKDIV8 is programmed, CLKPS bits are reset to357707E–AVR–11/08

“0011”, giving a division factor of 8 at start up. This feature should be used if the selected clock
source has a higher frequency than the maximum frequency of the device at the present operating conditions. Note that any value can be written to the CLKPS bits regardless of the CKDIV8
Fuse setting. The Application software must ensure that a sufficient division factor is chosen if
the selected clock source has a higher frequency than the maximum frequency of the device atthe present operating conditions. The device is shipped with the CKDIV8 Fuse programmed.

Table 6-9.

6.9

Clock Prescaler Select

CLKPS3

CLKPS2

CLKPS1

CLKPS0

Clock Division Factor

0

0

0

0

1

0

0

0

1

2

0

0

1

0

4

0

0

1

1

8

0

1

0

0

16

0

1

0

1

32

0

1

1

0

64

0

1

1

1

128

1

0

0

0

256

1

0

0

1

Reserved

1

0

1

0

Reserved

1

0

1

1

Reserved

1

1

0

0

Reserved

1

1

0

1

Reserved

1

1

1

0

Reserved

1

1

1

1

Reserved

PLL
The PLL is used to generate internal high frequency (48 MHz) clock for USB interface, the PLL
input is generated from an external low-frequency (the crystal oscillator or external clock input
pin from XTAL1).

6.9.1

36

Internal PLL for USB interface
The internal PLL in AT90USB82/162 generates a clock frequency that is 6x multiplied from nominally 8 MHz input. The source of the 8 MHz PLL input clock is the output of the internal PLL
clock prescaler that generates the 8 MHz.

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
Figure 6-6.

PLL Clocking System
PLLE

PLOCK

Lock
Detector

PLL clock
Prescaler

clk
8MHz

clkUSB (48MHz)

PLL
6xSystem Clock
Clock Mux (fuse)
Clock Switch
XTAL2
XTAL1

6.9.2

Int RC
8MHz.

Ext.

XTAL

PLL Control and Status Register – PLLCSR
Bit

7

6

5

$29 ($29)

4

3

2

1

0

PLLP2

PLLP1

PLLP0

PLLE

PLOCK

Read/Write

R

R

R

R

R

R

R/W

R

Initial Value

0

0

0

0

0

0

0/1

0

PLLCSR• Bit 7..5 – Res: Reserved Bits
These bits are reserved bits in the AT90USB82/162 and always read as zero.
• Bit 4..2 – PLLP2:0 PLL prescaler
These bits allow to configure the PLL input prescaler to generate the 8MHz input clock for the
PLL.
Table 6-10.

PLL input prescaler configurations

PLLP2

PLLP1

PLLP0

Clock Division Factor

0

0

0

1

0

0

1

2

0

1

0

Reserved

0

1

1

Reserved

100Reserved

10

1Reserved1

10

Reserved

1

1

1

Reserved• Bit 1 – PLLE: PLL Enable
When the PLLE is set, the PLL is started and if needed internal RC Oscillator is started as a PLL
reference clock. If PLL is selected as a system clock source the value for this bit is always 1.

377707E–AVR–11/08

• Bit 0 – PLOCK: PLL Lock Detector
When the PLOCK bit is set, the PLL is locked to the reference clock, and it is safe to enable PCK
for Timer/Counter1. After the PLL is enabled, it takes about 1ms up to 100 ms for the PLL to
lock.

38

AT90USB82/162

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AT90USB82/162
7. Power Distribution
The AT90USB82/162 product includes an internal 5V to 3.3V regulator thatallows to supply the USB pad (see Figure 7-1.) and, depending on the application, external components or even the microcontroller itself (see Figure 7-2.).
Figure 7-1.

5V configuration

USB or PS/2 connector
VBus or PS/2 Vcc (5V)UVCC

PS/2 Pad

UCAP

3.3V Reg

VCC

Band
Gap

AVR Core

AVCC

I/O

POR
BOD

PLL

Comparator

USB PadUVSS

VSS

Figure 7-2.

5V / 3.3V configuration

USB or PS/2 connector
VBus or PS/2 Vcc (5V)UVCC

PS/2 Pad

UCAP

3.3V Reg(3.3V)
VCC

Band
Gap

at least 50 mA
for external chips

AVR Core

AVCC

I/O

POR
BOD

PLL

Comparator

USB Pad
UVSS

VSS

39
7707E–AVR–11/08

Figure 7-3.

3.3V configuration(3.3V)
UVCC

PS/2 Pad

UCAP

3.3V Reg

VCC

Band
Gap

AVR Core

AVCC

I/O

POR
BOD

PLL

Comparator

USB PadUVSS

VSS

Important note:
In the 3.3V configuration, the internal regulator is bypassed. The regulator has to be disabled to
avoid extra power consumption.

7.0.1

Regulator Control Register – REGCR
Bit

7

6

5

4

3

2

1

0

-

-

-

-

-

-

-

REGDIS

Read/Write

R

R

R

R

R

R

R

R/W

Initial Value

0

0

0

0

0

0

0

0

REGCR

• Bit 0 – REGDIS: Regulator Disable
Set this bit to disable the internal 3.3V regulator. This bit should be used only in a full 3.3V application. This bit is reset to 0 in every case. The firmware has the responsability to set it after eachreset if required.

40

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AT90USB82/162
8. Power Management and Sleep Modes
Sleep modes enable the application to shut down unused modules in the MCU, thereby saving
power. The AVR provides various sleep modes allowing the user to tailor the power consumption to the application’s requirements.
To enter any of the five sleep modes, the SE bit in SMCR must be written to logic one and a
SLEEP instruction must be executed. The SM2, SM1, and SM0 bits in the SMCR Register selectwhich sleep mode (Idle, Power-down, Power-save, Standby or Extended standby) will be activated by the SLEEP instruction. See Table 8-1 for a summary. If an enabled interrupt occurs
while the MCU is in a sleep mode, the MCU wakes up. The MCU is then halted for four cycles in
addition to the start-up time, executes the interrupt routine, and resumes execution from the
instruction following SLEEP. The contents of the Register File and SRAM are unaltered when
the device wakes up from sleep. If a reset occurs during sleep mode, the MCU wakes up andexecutes from the Reset Vector.
Figure 6-1 on page 25 presents the different clock systems in the AT90USB82/162, and theirdistribution. The figure is helpful in selecting an appropriate sleep mode.
8.0.1

Sleep Mode Control Register – SMCR
The Sleep Mode Control Register contains control bits for power management.
Bit

7

6

5

4

3

2

1

0

–

–

–

–

SM2

SM1

SM0

SE

Read/Write

R

R

R

R

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

SMCR

• Bit 7-4 - Reserved bits
These bits are reserved and will always read as zero.
• Bits 3-1 – SM2..0: Sleep Mode Select Bits 2, 1, and 0
These bits select between the five available sleep modes as shown in Table 8-1.
Table 8-1.

Note:

Sleep Mode Select

SM2

SM1

SM0

Sleep Mode

0

0

0

Idle

0

0

1

Reserved010Power-down

0

1

1

Power-save

1

0

0

Reserved

10

1Reserved110Standby(1)

1

1

1

Extended Standby(1)1. Standby modes are only recommended for use with external crystals or resonators.

• Bit 0– SE: Sleep Enable
The SE bit must be written to logic one to make the MCU enter the sleep mode when the SLEEP
instruction is executed. To avoid the MCU entering the sleep mode unless it is the programmer’s

417707E–AVR–11/08

purpose, it is recommended to write the Sleep Enable (SE) bit to one just before the execution of
the SLEEP instruction and to clear it immediately after waking up.

8.1

Idle Mode
When the SM2..0 bits are written to 000, the SLEEP instruction makes the MCU enter Idle
mode, stopping the CPU but allowing the USB, SPI, USART, Analog Comparator, Timer/Counters, Watchdog, and the interrupt system to continue operating. This sleep mode basically halts
clkCPU and clkFLASH, while allowing the other clocks to run.
Idle mode enables the MCU to wake up from external triggered interrupts as well as internal
ones like the Timer Overflow, USART Transmit Complete or some USB interrupts (like SOFI,WAKEUPI...). If wake-up from the Analog Comparator interrupt is not required, the Analog Comparator can be powered down by setting the ACD bit in the Analog Comparator Control andStatus Register – ACSR. This will reduce power consumption in Idle mode.

8.2

Power-down Mode
When the SM2..0 bits are written to 010, the SLEEP instruction makes the MCU enter Powerdown mode. In this mode, the external Oscillator is stopped, while the external interrupts, the 2wire Serial Interface, and the Watchdog continue operating (if enabled). Only an External Reset,
a Watchdog Reset, a Brown-out Reset, 2-wire Serial Interface address match, an external levelinterrupt on INT7:4, an external interrupt on INT3:0, a pin change interrupt or an asynchronous
USB interrupt source (WAKEUPI only), can wake up the MCU. This sleep mode basically halts
all generated clocks, allowing operation of asynchronous modules only.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. Refer to “External Interrupts” on page 84
for details.
When waking up from Power-down mode, there is a delay from the wake-up condition occurs
until the wake-up becomes effective. This allows the clock to restart and become stable after
having been stopped. The wake-up period is defined by the same CKSEL Fuses that define theReset Time-out period, as described in “Clock Sources” on page 29.

8.3

Power-save Mode
When the SM2..0 bits are written to 011, the SLEEP instruction makes the MCU enter Powersave mode. This mode is identical to Power-down. This mode has been conserved for compatibility purpose with higher-end products.

8.4Standby Mode
When the SM2..0 bits are 110 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Standby mode. This mode is identical to Power-downwith the exception that the Oscillator is kept running. From Standby mode, the device wakes up
in six clock cycles.

8.5

Extended Standby Mode
When the SM2..0 bits are 111 and an external crystal/resonator clock option is selected, the
SLEEP instruction makes the MCU enter Extended Standby mode. This mode is identical toPower-save mode with the exception that the Oscillator is kept running. So Extended Standby

42

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AT90USB82/162
Mode is equivalent to Standy Mode, but is also conserved for compatibility purpose. From
Extended Standby mode, the device wakes up in six clock cycle.

Table 8-2.

Active Clock Domains and Wake-up Sources in the Different Sleep Modes.

8.6

X

X

X

Interrupts(1)USB AsynchonousInterrupts

X

USB Synchronous

X

Other I/O

X

WDT Interrupt

SPM/
EEPROM ReadyX

INT7:0 and
PCINT12-0

Idle

Wake-up Sources

Main ClockSourceEnabledclkIO

Sleep Mode

Oscillators

clkFLASH

clkCPU

Active Clock
Domains

X

Power-down

X

(1)

X

X

Power-save

X(1)

X

X

(1)

(1)

Standby

X

X

X

X

ExtendedStandby

X

X(1)

X

X

Notes:

1. Only recommended with external crystal or resonator selected as clock source.

Notes:

1. For INT7:4, only level interrupt.

Notes:

1. Asynchronous USB interrupt is WAKEUPI only.

Power Reduction Register
The Power Reduction Register, PRR, provides a method to stop the clock to individual peripherals to reduce power consumption. The current state of the peripheral is frozen and the I/Oregisters can not be read or written. Resources used by the peripheral when stopping the clock
will remain occupied, hence the peripheral should in most cases be disabled before stopping theclock. Waking up a module, which is done by clearing the bit in PRR, puts the module in thesame state as before shutdown.
Module shutdown can be used in Idle mode and Active mode to significantly reduce the overall
power consumption.

8.6.1

Power Reduction Register 0 - PRR0
Bit

7

6

5

4

3

2

1

0

-

-

PRTIM0–PRTIM1

PRSPI

-

-

Read/Write

R/W

R/W

R/W

R

R/W

R/W

R

R/W

Initial Value

0

0

0

0

0

0

0

0

PRR0

• Bit 7-6 - Reserved bits
These bits are reserved and will always read as zero.
• Bit 5 - PRTIM0: Power Reduction Timer/Counter0
Writing a logic one to this bit shuts down the Timer/Counter0 module. When the Timer/Counter0
is enabled, operation will continue like before the shutdown.

437707E–AVR–11/08

• Bit 4 - Res: Reserved bit
This bit is reserved and will always read as zero.
• Bit 3 - PRTIM1: Power Reduction Timer/Counter1
Writing a logic one to this bit shuts down the Timer/Counter1 module. When the Timer/Counter1
is enabled, operation will continue like before the shutdown.
• Bit 2 - PRSPI: Power Reduction Serial Peripheral Interface
Writing a logic one to this bit shuts down the Serial Peripheral Interface by stopping the clock to
the module. When waking up the SPI again, the SPI should be re initialized to ensure proper
operation.
• Bit 1 - Res: Reserved bit
These bits are reserved and will always read as zero.
• Bit 0 - Res: Reserved bit
These bits are reserved and will always read as zero.
8.6.2

Power Reduction Register 1 - PRR1
Bit

7

6

5

4

3

2

1

0

PRUSB

–

–

–

-

–

–

PRUSART1

Read/Write

R/W

R

R

R

R/W

R

R

R/W

Initial Value

0

0

0

0

0

0

0

0

PRR1

• Bit 7 - PRUSB: Power Reduction USB
Writing a logic one to this bit shuts down the USB by stopping the clock to the module. When
waking up the USB again, the USB should be re initialized to ensure proper operation.
• Bit 6..1 - Res: Reserved bits
These bits are reserved and will always read as zero.
• Bit 0 - PRUSART1: Power Reduction USART1
Writing a logic one to this bit shuts down the USART1 by stopping the clock to the module.
When waking up the USART1 again, the USART1 should be re initialized to ensure proper
operation.

8.7

Minimizing Power Consumption
There are several issues to consider when trying to minimize the power consumption in an AVR
controlled system. In general, sleep modes should be used as much as possible, and the sleep
mode should be selected so that as few as possible of the device’s functions are operating. All
functions not needed should be disabled. In particular, the following modules may need special
consideration when trying to achieve the lowest possible power consumption.

8.7.1

44

Analog Comparator
When entering Idle mode, the Analog Comparator should be disabled if not used. In other sleep
modes, the Analog Comparator is automatically disabled. However, if the Analog Comparator is
set up to use the Internal Voltage Reference as input, the Analog Comparator should be disabled in all sleep modes. Otherwise, the Internal Voltage Reference will be enabled,

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AT90USB82/162
independent of sleep mode. Refer to “Analog Comparator” on page 223 for details on how to
configure the Analog Comparator.
8.7.2

Brown-out Detector
If the Brown-out Detector is not needed by the application, this module should be turned off. If
the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep
modes, and hence, always consume power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to “Brown-out Detection” on page 49 for details
on how to configure the Brown-out Detector.

8.7.3

Internal Voltage Reference
The Internal Voltage Reference will be enabled when needed by the Brown-out Detection, or the
Analog Comparator. If these modules are disabled as described in the sections above, the internal voltage reference will be disabled and it will not be consuming power. When turned on again,
the user must allow the reference to start up before the output is used. If the reference is kept onin sleep mode, the output can be used immediately. Refer to “Internal Voltage Reference” onpage 52 for details on the start-up time.

8.7.4

Watchdog Timer
If the Watchdog Timer is not needed in the application, the module should be turned off. If theWatchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consumption. Refer to “Interrupts” on page 63 for details on how to configure the Watchdog Timer.

8.7.5

Port Pins
When entering a sleep mode, all port pins should be configured to use minimum power. The
most important is then to ensure that no pins drive resistive loads. In sleep modes where the I/Oclock (clkI/O) is stopped, the input buffers of the device will be disabled. This ensures that nopower is consumed by the input logic when not needed. In some cases, the input logic is neededfor detecting wake-up conditions, and it will then be enabled. Refer to the section “Digital Input
Enable and Sleep Modes” on page 71 for details on which pins are enabled. If the input buffer isenabled and the input signal is left floating or have an analog signal level close to VCC/2, theinput buffer will use excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal
level close to VCC/2 on an input pin can cause significant current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1). Refer to“Digital Input Disable Register 1 – DIDR1” on page 224 for details.

8.7.6

On-chip Debug System
If the On-chip debug system is enabled by the OCDEN Fuse and the chip enters sleep mode,the main clock source is enabled, and hence, always consumes power. In the deeper sleep
modes, this will contribute significantly to the total current consumption.

45
7707E–AVR–11/08

9. System Control and Reset
9.1

Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector must be a JMP – Absolute
Jump – instruction to the reset handling routine. If the program never enables an interrupt
source, the Interrupt Vectors are not used, and regular program code can be placed at theselocations. This is also the case if the Reset Vector is in the Application section while the Interrupt
Vectors are in the Boot section or vice versa. The circuit diagram in Figure 9-1 shows the reset
logic. Table 9-1 defines the electrical parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goesactive. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The different selections for the delay period are presented in “Clock Sources” on page 29.

9.2

Reset Sources
The AT90USB82/162 has five sources of reset:• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Resetthreshold (VPOT).
• External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
• Watchdog Reset. The MCU is reset when the Watchdog Timer period expires and theWatchdog is enabled. 9.9See “Watchdog Timer” on page 52.9.9• Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled.
• USB Reset. The MCU is reset when the USB macro is enabled and detects a USB Reset.
Note that with this reset the USB macro remains enabled so that the device stays attached tothe bus.

46

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AT90USB82/162
Figure 9-1.

Reset Logic
DATA BUS

PORF
BORF
EXTRF
WDRF
USBRF

MCU Status
Register (MCUSR)

Power-on Reset
Circuit

Brown-out
Reset Circuit

BODLEVEL [2..0]
Pull-up Resistor
SPIKE
FILTERUSB Device
Reset Detection

Watchdog
Oscillator

Clock
Generator

Delay Counters

CK

TIMEOUTCKSEL[3:0]
SUT[1:0]

Table 9-1.
SymbolVPOTParameter

Condition

Min

Power-on Reset Threshold Voltage (rising)(1)Power-on Reset Threshold Voltage (falling)

VPOR

VCC Start Voltage to ensure internal Power-on
Reset signal

-0.1

VCCRR

VCC Rise Rate to ensure internal Power_on
Reset signal

0.8

VRST

RESET Pin Threshold Voltage

0.2
Vcc

tRST

Minimum pulse width on RESET Pin

Notes:

9.3

Reset Characteristics

5V, 25°C

Typ

Max

Units

1.4

2.3

V

1.3

2.3

V

0.1

V
V/ms

0.85
Vcc
400

V
ns

1. The POR will not work unless the supply voltage has been below VPOT (falling)

Power-on Reset
A Power-on Reset (POR) pulse is generated by an On-chip detection circuit. The detection levelis defined in Table 9-1. The POR is activated whenever VCC is below the detection level. The
POR circuit can be used to trigger the start-up Reset, as well as to detect a failure in supply
voltage.
A Power-on Reset (POR) circuit ensures that the device is reset from Power-on. Reaching thePower-on Reset threshold voltage invokes the delay counter, which determines how long the47
7707E–AVR–11/08

device is kept in RESET after VCC rise. The RESET signal is activated again, without any delay,
when VCC decreases below the detection level.
Figure 9-2.

MCU Start-up, RESET Tied to VCC

VCC

RESET

VPOT

VRST

tTOUT

TIME-OUT

INTERNAL
RESET

Figure 9-3.

MCU Start-up, RESET Extended Externally

VCC

RESET

VPOT

VRST

tTOUT

TIME-OUT

INTERNAL
RESET

9.4

External Reset
An External Reset is generated by a low level on the RESET pin. Reset pulses longer than theminimum pulse width (see Table 9-1) will generate a reset, even if the clock is not running.
Shorter pulses are not guaranteed to generate a reset. When the applied signal reaches theReset Threshold Voltage – VRST – on its positive edge, the delay counter starts the MCU after
the Time-out period – tTOUT – has expired.
Figure 9-4.

External Reset During Operation
CC

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AT90USB82/162
9.5

Brown-out Detection
AT90USB82/162 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level
during operation by comparing it to a fixed trigger level. The trigger level for the BOD can beselected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike freeBrown-out Detection. The hysteresis on the detection level should be interpreted as V BOT+ =VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.
Table 9-2.

BODLEVEL Fuse Coding(1)BODLEVEL 2..0 Fuses

Min VBOT

111

Note:

Typ VBOT

Max VBOTUnits

BOD Disabled

110

2.5

2.7

2.9

101

2.7

2.9

3.1

100

2.8

3.0

3.2

011

3.3

3.5

3.7

010

3.4

3.6

3.8

001

3.8

4.0

4.2

000

4.1

4.3

4.5

V

1. VBOT may be below nominal minimum operating voltage for some devices. For devices where
this is the case, the device is tested down to VCC = VBOT during the production test. This guarantees that a Brown-Out Reset will occur before VCC drops to a voltage where correct
operation of the microcontroller is no longer guaranteed. The test is performed using
BODLEVEL = 110 for AT90USB82/162 and BODLEVEL = 101 for AT90USB82/162L.

Table 9-3.

Brown-out Characteristics

SymbolParameter

VHYSTBrown-out Detector Hysteresis

50

mV

tBOD

Min Pulse Width on Brown-out Reset

2

ns

Min

Typ

Max

Units

When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure9-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level(V BOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has
expired.
The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for longer than tBOD given in Table 9-1.

497707E–AVR–11/08

Figure 9-5.

Brown-out Reset During Operation
VCC

VBOT-

VBOT+

RESET

tTOUT

TIME-OUT

INTERNAL
RESET

9.6

Watchdog Reset
When the Watchdog times out, it will generate a short reset pulse of one CK cycle duration. On
the falling edge of this pulse, the delay timer starts counting the Time-out period tTOUT. Refer topage 52 for details on operation of the Watchdog Timer.
Figure 9-6.

Watchdog Reset During Operation

CC

CK

9.7

USB Reset
When the USB macro is enabled and configured with the USB reset MCU feature enabled, andif a valid USB Reset signalling is detected, the microcontroller is reset unless the USB macrothat remains enabled. This allows the device to stay attached to the bus during and after the
reset, while enhancing firmware reliability.

50

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AT90USB82/162
Figure 9-7.

USB Reset During Operation(USB Lines)

CC

9.7.1

t USBRSTMINDPEnd of Reset

USB TrafficDM

USB Traffic

MCU Status Register –MCUSR
The MCU Status Register provides information on which reset source caused an MCU reset.
Bit

7

6

5

4

3

2

1

0

–

–

USBRF

–

WDRF

BORF

EXTRF

PORF

Read/Write

R

R

R

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

See Bit Description

MCUSR• Bit 7-6 – Res: Reserved Bit
These bits are reserved and will always read as zero.
• Bit 5 – USBRF: USB Reset Flag
This bit is set if a USB Reset occurs. The bit is reset by a Power-on Reset, or by writing a logic
zero to the flag.
• Bit 4– Res: Reserved Bit
This bit is reserved.
• Bit 3 – WDRF: Watchdog Reset Flag
This bit is set if a Watchdog Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 2 – BORF: Brown-out Reset Flag
This bit is set if a Brown-out Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 1 – EXTRF: External Reset Flag
This bit is set if an External Reset occurs. The bit is reset by a Power-on Reset, or by writing a
logic zero to the flag.
• Bit 0 – PORF: Power-on Reset Flag
This bit is set if a Power-on Reset occurs. The bit is reset only by writing a logic zero to the flag.
To make use of the Reset Flags to identify a reset condition, the user should read and thenReset the MCUSR as early as possible in the program. If the register is cleared before anotherreset occurs, the source of the reset can be found by examining the Reset Flags.
517707E–AVR–11/08

9.8Internal Voltage Reference
AT90USB82/162 features an internal bandgap reference. This reference is used for Brown-out
Detection, and it can be used as an input to the Analog Comparator.

9.8.1

Voltage Reference Enable Signals and Start-up TimeThe voltage reference has a start-up time that may influence the way it should be used. The
start-up time is given in Table 9-4. To save power, the reference is not always turned on. The
reference is on during the following situations:
1. When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).
2. When the bandgap reference is connected to the Analog Comparator (by setting the
ACBG bit in ACSR).
Thus, when the BOD is not enabled, after setting the ACBG bit, the user must always allow thereference to start up before the output from the Analog Comparator is used. To reduce power
consumption in Power-down mode, the user can avoid the three conditions above to ensure thatthe reference is turned off before entering Power-down mode.
Table 9-4.
Symbol9.9Internal Voltage Reference Characteristics
Parameter

Condition

Min

Typ

Max

Units

VCC = 2.7V - 5.5V

1.0

1.1

1.2

V

70

µs

VBG

Bandgap reference voltage

tBG

Bandgap reference start-up time

-

40

IBG

Bandgap reference current
consumption

-

10

µA

Watchdog Timer
AT90USB82/162 has an Enhanced Watchdog Timer (WDT). The main features are:
• Clocked from separate On-chip Oscillator• 3 Operating modes– Interrupt– System Reset– Interrupt and System Reset

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AT90USB82/162• Selectable Time-out period from 16ms to 8s• Possible Hardware fuse Watchdog always on (WDTON) for fail-safe mode
• Early warning after one Time-Out period reached, programmable Reset (see operating modes)
after 2 Time-Out periods reached.

Watchdog Timer
WCLKD0WCLKD1128kHzOSCILLATOR

CLOCK
DIVIDER

OSC/1
OSC/3
OSC/5
OSC/7

WATCHDOG
RESET
WDE

OSC/2K
OSC/4K
OSC/8K
OSC/16K
OSC/32K
OSC/64K
OSC/128K
OSC/256K
OSC/512K
OSC/1024K

Figure 9-8.

WDP0
WDP1
WDP2
WDP3
MCU RESET

WDIF

WDIE

WDEWIE

INTERRUPTEARLY WARNINGINTERRUPTThe Watchdog Timer (WDT) is a timer counting cycles of a separate on-chip 128 kHz oscillator.
The WDT gives a early warning interrupt when the counter reaches a given time-out value. The
WDT gives an interrupt or a system reset when the counter reaches two times the given time-out
value. In normal operation mode, it is required that the system uses the WDR - Watchdog Timer
Reset - instruction to restart the counter before the time-out value is reached. If the systemdoesn't restart the counter, an interrupt or system reset will be issued.
In Interrupt mode, the WDT gives an interrupt when the timer expires two times. This interrupt
can be used to wake the device from sleep-modes, and also as a general system timer. One
example is to limit the maximum time allowed for certain operations, giving an interrupt when theoperation has run longer than expected.
In System Reset mode, the WDT gives a reset when the timer expires two times. This is typicallyused to prevent system hang-up in case of runaway code.
The third mode, Interrupt and System Reset mode, combines the other two modes by first giving
an interrupt and then switch to System Reset mode. This mode will for instance allow a safe
shutdown by saving critical parameters before a system reset.
In addition to these modes, the early warning interrupt can be enabled in order to generate aninterrupt when the WDT counter expires the first time.
The Watchdog always on (WDTON) fuse, if programmed, will force the Watchdog Timer to System Reset mode. With the fuse programmed the System Reset mode bit (WDE) and Interrupt
mode bit (WDIE) are locked to 1 and 0 respectively. To further ensure program security, alterations to the Watchdog set-up must follow timed sequences. The sequence for clearing WDE orchanging time-out configuration is as follows:

53
7707E–AVR–11/08

1. In the same operation, write a logic one to the Watchdog change enable bits WDCE
and WDE. A logic one must be written to WDE regardless of the previous value of the
WDE bit and even if it will be cleared after the operation.
2. Within the next four clock cycles, write the WDE and Watchdog prescaler bits (WDP) as
desired, but with the WDCE bit cleared. This must be done in one operation.
While the WDT prescaler allows only even division factors (2, 4, 8...), the WDT peripheral also
includes a clock divider that directly acts on the clock source. This divider handles odd division
factors (3, 5, 7). In combination with the prescaler, a large number of time-out values can beobtained.
The divider factor change is also ruled by the secure timed sequence : first the WDE and WDCE
bits must be set, and then four cycles are available to load the new divider value into the
WDTCKD register. Be aware that after this operation WDE will still be set. So keep in mind theimportance of order of operations. When setting up the WDT in Interrupt mode with specific values of prescaler and divider, the divider register must be loaded before the prescaler register :1. Set WDCE and WDE
2. Load the divider factor into WDTCKD
3. Wait WDCE being automatically cleared (just wait 2 more cycles)
4. Set again WDCE and WDE
5. Clear WDE, set WDIE and load the prescaler factor into WDTCSR in a same operation
6. Now the system is properly configured for Interrupt only mode. Inverting the two operations would have been resulted into “Reset and Interrupt mode” and needed a third
operation to clear WDE.

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AT90USB82/162
The following code example shows one assembly and one C function for turning off the Watchdog Timer. The example assumes that interrupts are controlled (e.g. by disabling interrupts
globally) so that no interrupts will occur during the execution of these functions.
Assembly Code Example(1)WDT_off:; Turn off global interrupt
cli; Reset Watchdog Timer
wdr; Clear WDRF in MCUSR
in

r16, MCUSR

andi

r16, (0xff & (0<<WDRF))

out

MCUSR, r16; Write logical one to WDCE and WDE; Keep old prescaler setting to prevent unintentional time-out
inr16, WDTCSR

orir16, (1<<WDCE) | (1<<WDE)

out

WDTCSR, r16; Turn off WDT
ldi

r16, (0<<WDE)

out

WDTCSR, r16; Turn on global interrupt
seiret

C Code Example(1)void WDT_off(void){__disable_interrupt();__watchdog_reset();/* Clear WDRF in MCUSR */MCUSR &= ~(1<<WDRF);/* Write logical one to WDCE and WDE *//* Keep old prescaler setting to prevent unintentional time-out */WDTCSR |= (1<<WDCE) | (1<<WDE);/* Turn off WDT */WDTCSR = 0x00;__enable_interrupt();}
Note:

1. The example code assumes that the part specific header file is included.

Note: If the Watchdog is accidentally enabled, for example by a runaway pointer or brown-out
condition, the device will be reset and the Watchdog Timer will stay enabled. If the code is not
set up to handle the Watchdog, this might lead to an eternal loop of time-out resets. To avoid thissituation, the application software should always clear the Watchdog System Reset Flag
(WDRF) and the WDE control bit in the initialisation routine, even if the Watchdog is not in use.

55
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The following code example shows one assembly and one C function for changing the time-out
value of the Watchdog Timer.
Assembly Code Example(1)
WDT_Prescaler_Change:; Turn off global interrupt
cli; Reset Watchdog Timer
wdr; Start timed sequenceinr16, WDTCSR

orir16, (1<<WDCE) | (1<<WDE)

out

WDTCSR, r16; --Got four cycles to set the new values from here -; Set new prescaler(time-out) value = 64K cycles (~0.5 s)
ldi

r16, (1<<WDE) | (1<<WDP2) | (1<<WDP0)out

WDTCSR, r16; --Finished setting new values, used 2 cycles -; Turn on global interrupt
seiret

C Code Example(1)void WDT_Prescaler_Change(void){__disable_interrupt();__watchdog_reset();/* Start timed

equence */WDTCSR |= (1<<WDCE) | (1<<WDE);/* Set new prescaler(time-out) value = 64K cycles (~0.5 s) */WDTCSR= (1<<WDE) | (1<<WDP2) | (1<<WDP0);__enable_interrupt();}
Note:

1. The example code assumes that the part specific header file is included.

Note: The Watchdog Timer should be reset before any change of the WDP bits, since a change
in the WDP bits can result in a time-out when switching to a shorter time-out period.
9.9.1

Watchdog Timer Control Register - WDTCSR
Bit

7

6

5

4

3

2

1

0

WDIF

WDIE

WDP3

WDCE

WDE

WDP2

WDP1

WDP0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

X

0

0

0

WDTCSR• Bit 7 - WDIF: Watchdog Interrupt Flag
This bit is set when a time-out occurs twice in the Watchdog Timer and if the Watchdog Timer isconfigured for interrupt. WDIF is automatically cleared by hardware when executing the corre-

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AT90USB82/162
sponding interrupt handling vector. Alternatively, WDIF is cleared by writing a logic one to theflag. When the I-bit in SREG and WDIE are set, the Watchdog Time-out Interrupt is executed.
• Bit 6 - WDIE: Watchdog Interrupt Enable
When this bit is written to one and the I-bit in the Status Register is set, the Watchdog Interrupt isenabled. If WDE is cleared in combination with this setting, the Watchdog Timer is in Interrupt
Mode, and the corresponding interrupt is executed if time-out in the Watchdog Timer occurs.
If WDE is set, the Watchdog Timer is in Interrupt and System Reset Mode. Two consecutives
times-out in the Watchdog Timer will set WDIF. Executing the corresponding interrupt vector willclear WDIE and WDIF automatically by hardware : the Watchdog goes to System Reset Mode.
This is useful for keeping the Watchdog Timer security while using the interrupt. To reinitialize
the Interrupt and System Reset Mode, WDIE must be set after each interrupt. This should however not be done within the interrupt service routine itself, as this might compromise the safetyfunction of the Watchdog System Reset mode. If the interrupt is not executed before the nexttime-out, a System Reset will be applied.
Table 9-5.

Watchdog Timer Configuration

WDTON (Fuse)

WDE

WDIE

Mode

Action on 2x Time-out

1 (unprogrammed)

00StoppedNone

1 (unprogrammed)

01Interrupt Mode

Interrupt

1 (unprogrammed)

10

System Reset ModeReset

1 (unprogrammed)

1

1Interrupt and System
Reset Mode

Interrupt, then go to
System Reset Mode0 (programmed)xx

System Reset ModeReset

• Bit 4 - WDCE: Watchdog Change Enable
This bit is used in timed sequences for changing WDE and prescaler bits. To clear the WDE bit,
and/or change the prescaler bits, WDCE must be set.
Once written to one, hardware will clear WDCE after four clock cycles.
• Bit 3 - WDE: Watchdog System Reset Enable
WDE is overridden by WDRF in MCUSR. This means that WDE is always set when WDRF isset. To clear WDE, WDRF must be cleared first. This feature ensures multiple resets during conditions causing failure, and a safe start-up after the failure.
• Bit 5, 2..0 - WDP3..0: Watchdog Timer Prescaler 3, 2, 1 and 0
The WDP3..0 bits determine the Watchdog Timer prescaling when the Watchdog Timer is running. The different prescaling values and their corresponding time-out periods are shown in
Table 9-6 on page 59.
9.9.2

Watchdog Timer Clock Divider Register - WDTCKD
Bit

7

6

5

4

3

2

1

0

-

-

-

-

WDEWIF

WDEWIE

WCLKD
1

WCLKD
0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

WDTCKD57
7707E–AVR–11/08

• Bit 7-4 - Reserved bits
These bits are reserved and will always read as zero.
• Bit 3 - WDEWIF: Watchdog Early Warning Interrupt Flag
This bit is set when a first time-out occurs in the Watchdog Timer and if the WDEWIE bit isenabled. WDEWIF is automatically cleared by hardware when executing the corresponding
interrupt handling vector. Alternatively, WDIF can be cleared by writing a logic one to the flag.
When the I-bit in SREG and WDEWIE are set, the Watchdog Time-out Interrupt is executed.
• Bit 2 - WDEWIE: Watchdog Early Warning Interrupt Enable
When this bit has been set by software, an interrupt will be generated on the watchdog interrupt
vector when the Early warning flag is set to one by hardware.
• Bit 1:0 - WCLKD[1:0]: Watchdog Timer Clock Divider– WCLKD = 0 : ClkWDT = Clk128k– WCLKD = 1 : ClkWDT = Clk128k / 3– WCLKD = 2 : ClkWDT = Clk128k / 5– WCLKD = 3 : ClkWDT = Clk128k / 7

58

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AT90USB82/162.

Table 9-6.

Watchdog Timer Prescale Select, DIV = 0 (CLKwdt = CLK128 / 1)

Early warning Typical
Time-out at
VCC = 5.0V

Watchdog
Reset/Interrupt Typical
Time-out at
VCC = 5.0V

WDP3

WDP2

WDP1

WDP0

Number of WDT Oscillator
Cycles before 1st time-out(Early warning)

0

0

0

0

2K (2048) cycles

16 ms

32 ms

0

0

0

1

4K (4096) cycles

32 ms

64 ms

0

0

1

0

8K (8192) cycles

64 ms

128 ms0011

16K (16384) cycles

0.125 s0.250 s

0

1

0

0

32K (32768) cycles

0.25 s

0.5 s

0

1

0

1

64K (65536) cycles

0.5 s

1.0 s

0

1

1

0

128K (131072) cycles

1.0 s

2.0 s

0

1

1

1

256K (262144) cycles

2.0 s

4.0 s

1

0

0

0

512K (524288) cycles

4.0 s

8.0 s

1

0

0

1

1024K (1048576) cycles

8.0 s

16.0 s

1

0

1

0

1

0

1

1

1

1

0

0

1

1

0

1

1

1

1

0

1

1

1

1

Reserved

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7707E–AVR–11/08

Table 9-7.

Watchdog Timer Prescale Select, DIV = 1 (CLKwdt = CLK128 / 3)

Early warning Typical
Time-out at
VCC = 5.0V

Watchdog
Reset/Interrupt Typical
Time-out at
VCC = 5.0V

WDP3

WDP2

WDP1

WDP0

Number of WDT Oscillator
Cycles before 1st time-out(Early warning)

0

0

0

0

2K (2048) cycles

48 ms

96 ms

0

0

0

1

4K (4096) cycles

96 ms

192 ms0010

8K (8192) cycles

192 ms

384 ms0011

16K (16384) cycles

0.375 s0.75 s010032K (32768) cycles

0.75 s

1.5 s

0

1

0

1

64K (65536) cycles

1.5 s

3s

0

1

1

0

128K (131072) cycles

3s

6s

0

1

1

1

256K (262144) cycles

6s

12 s

1

0

0

0

512K (524288) cycles

12 s

24 s

1

0

0

1

1024K (1048576) cycles

24 s

48 s

1

0

1

0

1

0

1

1

1

1

0

0

1

1

0

1

1

1

1

0

1

1

1

1

60

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AT90USB82/162
Table 9-8.

Watchdog Timer Prescale Select, DIV = 2 (CLKwdt = CLK128 / 5)

Early warning Typical
Time-out at
VCC = 5.0V

Watchdog
Reset/Interrupt Typical
Time-out at
VCC = 5.0V

WDP3

WDP2

WDP1

WDP0

Number of WDT Oscillator
Cycles before 1st time-out(Early warning)

0

0

0

0

2K (2048) cycles

80 ms

160 ms000

1

4K (4096) cycles

160 ms

320 ms0010

8K (8192) cycles

320 ms

640 ms0011

16K (16384) cycles

0.625 s1.25 s010032K (32768) cycles

1.25 s

2.5 s

0

1

0

1

64K (65536) cycles

2.5 s

5s

0

1

1

0

128K (131072) cycles

5s

10 s

0

1

1

1

256K (262144) cycles

10 s

20 s

1

0

0

0

512K (524288) cycles

20 s

40 s

1

0

0

1

1024K (1048576) cycles

40 s

80 s

1

0

1

0

1

0

1

1

1

1

0

0

1

1

0

1

1

1

1

0

1

1

1

1

Reserved

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Table 9-9.

Watchdog Timer Prescale Select, DIV = 3 (CLKwdt = CLK128 / 7)

Early warning Typical
Time-out at
VCC = 5.0V

Watchdog
Reset/Interrupt Typical
Time-out at
VCC = 5.0V

WDP3

WDP2

WDP1

WDP0

Number of WDT Oscillator
Cycles before 1st time-out(Early warning)

0

0

0

0

2K (2048) cycles

112 ms

224 ms000

1

4K (4096) cycles

224 ms

448 ms0010

8K (8192) cycles

448 ms

896 ms0011

16K (16384) cycles

0.875 s1.75 s010032K (32768) cycles

1.75 s

3.5 s

0

1

0

1

64K (65536) cycles

3.5 s

7s

0

1

1

0

128K (131072) cycles

7s

14 s

0

1

1

1

256K (262144) cycles

14 s

28 s

1

0

0

0

512K (524288) cycles

28 s

56 s

1

0

0

1

1024K (1048576) cycles

56 s

112 s

1

0

1

0

1

0

1

1

1

1

0

0

1

1

0

1

1

1

1

0

1

1

1

1

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AT90USB82/162
10. Interrupts
This section describes the specifics of the interrupt handling as performed in AT90USB82/162.
For a general explanation of the AVR interrupt handling, refer to “Reset and Interrupt Handling”
on page 13.

10.1

Interrupt Vectors in AT90USB82/162
Table 10-1.

Reset and Interrupt Vectors

VectorNo.

ProgramAddress(2)SourceInterrupt Definition

1$0000(1)RESET

External Pin, Power-on Reset, Brown-out Reset,
Watchdog Reset, USB Reset and debugWIRE AVR
Reset

2

$0002

INT0

External Interrupt Request 0

3

$0004

INT1

External Interrupt Request 1

4

$0006

INT2

External Interrupt Request 2

5

$0008

INT3

External Interrupt Request 3

6

$000A

INT4

External Interrupt Request 4

7

$000C

INT5

External Interrupt Request 5

8

$000E

INT6

External Interrupt Request 6

9

$0010

INT7

External Interrupt Request 7

10

$0012

PCINT0Pin Change Interrupt Request 0

11

$0014

PCINT1

Pin Change Interrupt Request 1

12

$0016

USB General

USB General Interrupt request

13

$0018

USB Endpoint

USB Endpoint Interrupt request

14

$001A

WDT

Watchdog Time-out Interrupt

15

$001C

TIMER1 CAPT

Timer/Counter1 Capture Event

16

$001E

TIMER1 COMPA

Timer/Counter1 Compare Match A

17

$0020

TIMER1 COMPB

Timer/Counter1 Compare Match B

18

$0022

TIMER1 COMPC

Timer/Counter1 Compare Match C

19

$0024

TIMER1 OVF

Timer/Counter1 Overflow

20

$0026

TIMER0 COMPA

Timer/Counter0 Compare Match A

21

$0028

TIMER0 COMPB

Timer/Counter0 Compare match B

22

$002A

TIMER0 OVF

Timer/Counter0 Overflow

23

$002C

SPI, STCSPI Serial Transfer Complete

24

$002E

USART1 RX

USART1 Rx Complete

25

$0030

USART1 UDRE

USART1 Data Register Empty

26

$0032

USART1TX

USART1 Tx Complete

637707E–AVR–11/08

Table 10-1.

Reset and Interrupt Vectors (Continued)

VectorNo.

ProgramAddress(2)

27
28
29
Notes:

SourceInterrupt Definition$0034

ANALOG COMP

Analog Comparator$0036

EE READYEEPROM Ready$0038

SPM READYStore Program Memory Ready

1. When the BOOTRST Fuse is programmed, the device will jump to the Boot Loader address at
reset, see “Memory Programming” on page 243.
2. When the IVSEL bit in MCUCR is set, Interrupt Vectors will be moved to the start of the Boot
Flash Section. The address of each Interrupt Vector will then be the address in this tableadded to the start address of the Boot Flash Section. Moreover, contrary to other 8K/16K
devices, the interrupt vectors spacing remains identical (2 words) for both 8KB and 16KB
versions.

Table 10-2 shows reset and Interrupt Vectors placement for the various combinations of
BOOTRST and IVSEL settings. If the program never enables an interrupt source, the Interrupt
Vectors are not used, and regular program code can be placed at these locations. This is also
the case if the Reset Vector is in the Application section while the Interrupt Vectors are in the
Boot section or vice versa.

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AT90USB82/162
Table 10-2.

Reset and Interrupt Vectors Placement(1)BOOTRST

IVSEL

1

Note:

Reset Address

Interrupt Vectors Start Address

00x00000x00021

10x0000

Boot Reset Address + 0x0002

00Boot Reset Address

0x0002

0

1

Boot Reset Address

Boot Reset Address + 0x0002

1. The Boot Reset Address is shown in Table 23-8 on page 239. For the BOOTRST Fuse “1”means unprogrammed while “0” means programmed.

10.1.1Moving Interrupts Between Application and Boot Space
The General Interrupt Control Register controls the placement of the Interrupt Vector table.

10.1.2MCU Control Register – MCUCR
Bit

7

6

5

4

3

2

1

0

JTD

–

–

PUD

–

–

IVSEL

IVCE

Read/Write

R/W

R

R

R/W

R

R

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

MCUCR

• Bit 1 – IVSEL: Interrupt Vector SelectWhen the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flashmemory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot
Loader section of the Flash. The actual address of the start of the Boot Flash Section is determined by the BOOTSZ Fuses. Refer to the section “Memory Programming” on page 243 fordetails. To avoid unintentional changes of Interrupt Vector tables, a special write procedure mustbe followed to change the IVSEL bit:a. Write the Interrupt Vector Change Enable (IVCE) bit to one.
b. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabledin the cycle IVCE is set, and they remain disabled until after the instruction following the write to
IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status
Register is unaffected by the automatic disabling.
Note:

If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is programmed, interrupts are disabled while executing from the Application section. If Interrupt Vectors
are placed in the Application section and Boot Lock bit BLB12 is programed, interrupts are disabled while executing from the Boot Loader section. Refer to the section “Memory
Programming” on page 243 for details on Boot Lock bits.

• Bit 0 – IVCE: Interrupt Vector Change Enable

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The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is cleared byhardware four cycles after it is written or when IVSEL is written. Setting the IVCE bit will disableinterrupts, as explained in the IVSEL description above. See Code Example below.
Assembly Code Example
Move_interrupts:; Enable change of Interrupt Vectors
ldi r16, (1<<IVCE)
out MCUCR, r16; Move interrupts to Boot Flash section
ldi r16, (1<<IVSEL)
out MCUCR, r16
ret

C Code Example
void Move_interrupts(void){/* Enable change of Interrupt Vectors */MCUCR = (1<<IVCE);/* Move interrupts to Boot Flash section */MCUCR = (1<<IVSEL);}

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AT90USB82/162
11. I/O-Ports
11.1

Introduction
All AVR ports have true Read-Modify-Write functionality when used as general digital I/O ports.
This means that the direction of one port pin can be changed without unintentionally changing
the direction of any other pin with the SBI and CBI instructions. The same applies when changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as
input). Each output buffer has symmetrical drive characteristics with both high sink and source
capability. The pin driver is strong enough to drive LED displays directly. All port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance. All I/O pins haveprotection diodes to both VCC and Ground as indicated in Figure 11-1. Refer to “Electrical Characteristics” on page 262 for a complete list of parameters.
Figure 11-1. I/O Pin Equivalent Schematic

Rpu
Logic

Pxn

Cpin

See Figure"General Digital I/O" for
Details

All registers and bit references in this section are written in general form. A lower case “x” represents the numbering letter for the port, and a lower case “n” represents the bit number. However,when using the register or bit defines in a program, the precise form must be used. For example,
PORTB3 for bit no. 3 in Port B, here documented generally as PORTxn. The physical I/O Registers and bit locations are listed in “Register Description for I/O-Ports” on page 82.
Three I/O memory address locations are allocated for each port, one each for the Data Register– PORTx, Data Direction Register – DDRx, and the Port Input Pins – PINx. The Port Input Pins
I/O location is read only, while the Data Register and the Data Direction Register are read/write.
However, writing a logic one to a bit in the PINx Register, will result in a toggle in the corresponding bit in the Data Register. In addition, the Pull-up Disable – PUD bit in MCUCR disables thepull-up function for all pins in all ports when set.
Using the I/O port as General Digital I/O is described in “Ports as General Digital I/O” on page
68. Most port pins are multiplexed with alternate functions for the peripheral features on thedevice. How each alternate function interferes with the port pin is described in “Alternate Port
Functions” on page 72. Refer to the individual module sections for a full description of the alternate functions.

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Note that enabling the alternate function of some of the port pins does not affect the use of theother pins in the port as general digital I/O.

11.2

Ports as General Digital I/O
The ports are bi-directional I/O ports with optional internal pull-ups. Figure 11-2 shows a functional description of one I/O-port pin, here generically called Pxn.
Figure 11-2. General Digital I/O(1)

PUD

Q

D

DDxn
Q CLR

WDx

RESET

DATA BUS

RDx

1
Q

Pxn

D

0

PORTxn
Q CLR

RESET
WRx
SLEEP

WPx

RRx

SYNCHRONIZER
D

Q

L

Q

D

RPx

Q

PINxn
Q

clk I/OPUD:
SLEEP:
clkI/O:

Note:

11.2.1PULLUP DISABLESLEEP CONTROLI/O CLOCK

WDx:
RDx:
WRx:
RRx:
RPx:
WPx:

WRITE DDRx
READ DDRx
WRITE PORTx
READ PORTx REGISTERREAD PORTx PIN
WRITE PINx REGISTER

1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports.

Configuring the Pin
Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. As shown in “Register
Description for I/O-Ports” on page 82, the DDxn bits are accessed at the DDRx I/O address, thePORTxn bits at the PORTx I/O address, and the PINxn bits at the PINx I/O address.
The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is written logic one,
Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is configured as an input
pin.
If PORTxn is written logic one when the pin is configured as an input pin, the pull-up resistor isactivated. To switch the pull-up resistor off, PORTxn has to be written logic zero or the pin has tobe configured as an output pin. The port pins are tri-stated when reset condition becomes active,
even if no clocks are running.

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AT90USB82/162
If PORTxn is written logic one when the pin is configured as an output pin, the port pin is driven
high (one). If PORTxn is written logic zero when the pin is configured as an output pin, the port
pin is driven low (zero).
11.2.2

Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.
Note that the SBI instruction can be used to toggle one single bit in a port.

11.2.3

Switching Between Input and Output
When switching between tri-state ({DDxn, PORTxn} = 0b00) and output high ({DDxn, PORTxn}= 0b11), an intermediate state with either pull-up enabled {DDxn, PORTxn} = 0b01) or output
low ({DDxn, PORTxn} = 0b10) occurs. Normally, the pull-up enabled state is fully acceptable, asa high-impedant environment will not notice the difference between a strong high driver and apull-up. If this is not the case, the PUD bit in the MCUCR Register can be set to disable all pullups in all ports.
Switching between input with pull-up and output low generates the same problem. The user
must use either the tri-state ({DDxn, PORTxn} = 0b00) or the output high state ({DDxn, PORTxn}= 0b11) as an intermediate step.
Table 11-1 summarizes the control signals for the pin value.
Table 11-1.

11.2.4

Port Pin Configurations

DDxn

PORTxnPUD(in MCUCR)

I/O

Pull-up

0

0

X

Input

No

Tri-state (Hi-Z)

0

1

0

Input

Yes

Pxn will source current if ext. pulled
low.

0

1

1

Input

No

Tri-state (Hi-Z)

1

0

X

OutputNo

Output Low (Sink)

1

1

X

OutputNo

Output High (Source)

Comment

Reading the Pin Value
Independent of the setting of Data Direction bit DDxn, the port pin can be read through the
PINxn Register bit. As shown in Figure 11-2, the PINxn Register bit and the preceding latch constitute a synchronizer. This is needed to avoid metastability if the physical pin changes value
near the edge of the internal clock, but it also introduces a delay. Figure 11-3 shows a timing diagram of the synchronization when reading an externally applied pin value. The maximum andminimum propagation delays are denoted tpd,max and tpd,min respectively.

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Figure 11-3. Synchronization when Reading an Externally Applied Pin value

SYSTEM CLKINSTRUCTIONS

XXX

XXX

in r17, PINx

SYNC LATCH
PINxn
r17

0x00

0xFF

t pd, maxt pd, minConsider the clock period starting shortly after the first falling edge of the system clock. The latch
is closed when the clock is low, and goes transparent when the clock is high, as indicated by theshaded region of the “SYNC LATCH” signal. The signal value is latched when the system clock
goes low. It is clocked into the PINxn Register at the succeeding positive clock edge. As indicated by the two arrows tpd,max and tpd,min, a single signal transition on the pin will be delayed
between ½ and 1½ system clock period depending upon the time of assertion.
When reading back a software assigned pin value, a nop instruction must be inserted as indicated in Figure 11-4. The out instruction sets the “SYNC LATCH” signal at the positive edge ofthe clock. In this case, the delay tpd through the synchronizer is 1 system clock period.
Figure 11-4. Synchronization when Reading a Software Assigned Pin ValueSYSTEM CLK
r16
INSTRUCTIONS

0xFF

out PORTx, r16

nop

in r17, PINx

SYNC LATCH
PINxn
r17

0x00

0xFF

t pd

The following code example shows how to set port B pins 0 and 1 high, 2 and 3 low, and define
the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. The resulting pin
values are read back again, but as previously discussed, a nop instruction is included to be able
to read back the value recently assigned to some of the pins.
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AT90USB82/162
Assembly Code Example(1)...
; Define pull-ups and set outputs high; Define directions for port pins
ldi

r16,(1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0)

ldi

r17,(1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0)

out

PORTB,r16

out

DDRB,r17; Insert nop for synchronizationnop; Read port pins
inr16,PINB...

C Code Example
unsigned char i;...
/* Define pull-ups and set outputs high *//* Define directions for port pins */PORTB = (1<<PB7)|(1<<PB6)|(1<<PB1)|(1<<PB0);DDRB = (1<<DDB3)|(1<<DDB2)|(1<<DDB1)|(1<<DDB0);/* Insert nop for synchronization*/__no_operation();/* Read port pins */i = PINB;
...
Note:

11.2.5

1. For the assembly program, two temporary registers are used to minimize the time from pullups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3
as low and redefining bits 0 and 1 as strong high drivers.

Digital Input Enable and Sleep Modes
As shown in Figure 11-2, the digital input signal can be clamped to ground at the input of theschmitt-trigger. The signal denoted SLEEP in the figure, is set by the MCU Sleep Controller inPower-down mode, Power-save mode, and Standby mode to avoid high power consumption ifsome input signals are left floating, or have an analog signal level close to VCC/2.
SLEEP is overridden for port pins enabled as external interrupt pins. If the external interrupt
request is not enabled, SLEEP is active also for these pins. SLEEP is also overridden by various
other alternate functions as described in “Alternate Port Functions” on page 72.
If a logic high level (“one”) is present on an asynchronous external interrupt pin configured as“Interrupt on Rising Edge, Falling Edge, or Any Logic Change on Pin” while the external interrupt
is not enabled, the corresponding External Interrupt Flag will be set when resuming from theabove mentioned Sleep mode, as the clamping in these sleep mode produces the requested
logic change.

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11.2.6

Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Even
though most of the digital inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current consumption in all other modes where the digital
inputs are enabled (Reset, Active mode and Idle mode).
The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.
In this case, the pull-up will be disabled during reset. If low power consumption during reset isimportant, it is recommended to use an external pull-up or pull-down. Connecting unused pins
directly to VCC or GND is not recommended, since this may cause excessive currents if the pin is
accidentally configured as an output.

11.3

Alternate Port Functions
Most port pins have alternate functions in addition to being general digital I/Os. Figure 11-5
shows how the port pin control signals from the simplified Figure 11-2 can be overridden byalternate functions. The overriding signals may not be present in all port pins, but the figure
serves as a generic description applicable to all port pins in the AVR microcontroller family.
Figure 11-5. Alternate Port Functions(1)PUOExnPUOVxn1

PUD

0

DDOExnDDOVxn
1
Q
D
DDxn

0

Q CLR

WDx

PVOExn

RESET
RDx

1

DATA BUSPVOVxn

1

Pxn
Q

0

D

0

PORTxnPTOExnQ CLRDIEOExn

WPx
DIEOVxn

RESET

WRx

1
0

RRx

SLEEP
SYNCHRONIZER
D

SET

Q

RPx

Q

D

PINxn
L CLR Q

CLR

Q

clk I/O

DIxn

AIOxn

PUOExn:PUOVxn:DDOExn:DDOVxn:PVOExn:PVOVxn:DIEOExn:
DIEOVxn:
SLEEP:
PTOExn:72

Pxn PULL-UP OVERRIDE ENABLE
Pxn PULL-UP OVERRIDE VALUE
Pxn DATA DIRECTION OVERRIDE ENABLE
Pxn DATA DIRECTION OVERRIDE VALUE
Pxn PORT VALUE OVERRIDE ENABLE
Pxn PORT VALUE OVERRIDE VALUE
Pxn DIGITAL INPUT-ENABLE OVERRIDE ENABLE
Pxn DIGITAL INPUT-ENABLE OVERRIDE VALUESLEEP CONTROL
Pxn, PORT TOGGLE OVERRIDE ENABLE

AT90USB82/162

PUD:
WDx:
RDx:
RRx:
WRx:
RPx:
WPx:
clkI/O:
DIxn:
AIOxn:PULLUP DISABLE
WRITE DDRx
READ DDRx
READ PORTx REGISTERWRITE PORTx
READ PORTx PIN
WRITE PINx
I/O CLOCKDIGITAL INPUT PIN n ON PORTx
ANALOG INPUT/OUTPUT PIN n ON PORTx

7707E–AVR–11/08

AT90USB82/162
Note:

1. WRx, WPx, WDx, RRx, RPx, and RDx are common to all pins within the same port. clkI/O,
SLEEP, and PUD are common to all ports. All other signals are unique for each pin.

Table 11-2 summarizes the function of the overriding signals. The pin and port indexes from Figure 11-5 are not shown in the succeeding tables. The overriding signals are generated internallyin the modules having the alternate function.
Table 11-2.

Generic Description of Overriding Signals for Alternate Functions

Signal Name

Full Name

Description

PUOE

Pull-up Override
EnableIf this signal is set, the pull-up enable is controlled by the PUOV
signal. If this signal is cleared, the pull-up is enabled when
{DDxn, PORTxn, PUD} = 0b010.

PUOV

Pull-up Override
Value

If PUOE is set, the pull-up is enabled/disabled when PUOV is
set/cleared, regardless of the setting of the DDxn, PORTxn,
and PUD Register bits.

DDOE

Data Direction
Override Enable

If this signal is set, the Output Driver Enable is controlled by the
DDOV signal. If this signal is cleared, the Output driver isenabled by the DDxn Register bit.

DDOV

Data Direction
Override Value

If DDOE is set, the Output Driver is enabled/disabled when
DDOV is set/cleared, regardless of the setting of the DDxn
Register bit.

PVOEPort Value
Override Enable

If this signal is set and the Output Driver is enabled, the port
value is controlled by the PVOV signal. If PVOE is cleared, andthe Output Driver is enabled, the port Value is controlled by the
PORTxn Register bit.

PVOVPort Value
Override ValueIf PVOE is set, the port value is set to PVOV, regardless of thesetting of the PORTxn Register bit.

PTOE

Port Toggle
Override Enable

If PTOE is set, the PORTxn Register bit is inverted.

DIEOE

Digital Input
Enable Override
EnableIf this bit is set, the Digital Input Enable is controlled by the
DIEOV signal. If this signal is cleared, the Digital Input Enable
is determined by MCU state (Normal mode, sleep mode).

DIEOV

Digital Input
Enable Override
Value

If DIEOE is set, the Digital Input is enabled/disabled when
DIEOV is set/cleared, regardless of the MCU state (Normalmode, sleep mode).

DI

Digital Input

This is the Digital Input to alternate functions. In the figure, thesignal is connected to the output of the schmitt trigger but
before the synchronizer. Unless the Digital Input is used as aclock source, the module with the alternate function will use its
own synchronizer.

AIO

AnalogInput/Output

This is the Analog Input/output to/from alternate functions. The
signal is connected directly to the pad, and can be used bidirectionally.

The following subsections shortly describe the alternate functions for each port, and relate theoverriding signals to the alternate function. Refer to the alternate function description for further
details.
11.3.1MCU Control Register – MCUCR
Bit

7

6

5

4

3

2

1

0

JTD

–

–

PUD

–

–

IVSEL

IVCE

MCUCR

73
7707E–AVR–11/08

Read/Write

R/W

R

R

R/W

R

R

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

• Bit 4 – PUD: Pull-up Disable
When this bit is written to one, the pull-ups in the I/O ports are disabled even if the DDxn and
PORTxn Registers are configured to enable the pull-ups ({DDxn, PORTxn} = 0b01). See “Configuring the Pin” on page 68 for more details about this feature.
11.3.2

Alternate Functions of Port B
The Port B pins with alternate functions are shown in Table 11-3.
Table 11-3.
Port Pin

Port B Pins Alternate Functions
Alternate Functions

PB7

OC0A/OC1C/PCINT7 (Output Compare and PWM Output A for Timer/Counter0, Output
Compare and PWM Output C for Timer/Counter1 or Pin Change Interrupt 7)

PB6

PCINT6 (Pin Change Interrupt 6)

PB5

PCINT5 (Pin Change Interrupt 5)

PB4

T1/PCINT4 (Timer/Counter1 Clock Input or Pin Change Interrupt 4)

PB3

PDO/MISO/PCINT3 (Programming Data Output or SPI Bus Master Input/Slave Output or
Pin Change Interrupt 3)

PB2

PDI/MOSI/PCINT2 (Programming Data Input or SPI Bus Master Output/Slave Input or Pin
Change Interrupt 2)

PB1

SCLK/PCINT1 (SPI Bus Serial Clock or Pin Change Interrupt 1)

PB0

SS/PCINT0 (SPI Slave Select input or Pin Change Interrupt 0)

The alternate pin configuration is as follows:• OC0A/OC1C/PCINT7, Bit 7
OC0A, Output Compare Match A output: The PB7 pin can serve as an external output for theTimer/Counter0 Output Compare. The pin has to be configured as an output (DDB7 set “one”) toserve this function. The OC0A pin is also the output pin for the PWM mode timer function.
OC1C, Output Compare Match C output: The PB7 pin can serve as an external output for theTimer/Counter1 Output Compare C. The pin has to be configured as an output (DDB7 set “one”)
to serve this function. The OC1C pin is also the output pin for the PWM mode timer function.
PCINT7, Pin Change Interrupt source 7: The PB7 pin can serve as an external interrupt source.
• PCINT6, Bit 6
PCINT6, Pin Change Interrupt source 6: The PB6 pin can serve as an external interrupt source.
• PCINT5, Bit 5
PCINT5, Pin Change Interrupt source 5: The PB5 pin can serve as an external interrupt source.
• T1/PCINT4, Bit 4
T1, Timer/Counter1 counter source.
PCINT4, Pin Change Interrupt source 4: The PB4 pin can serve as an external interrupt source.
• PDO/MISO/PCINT3 – Port B, Bit 3
74

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AT90USB82/162
PDO, SPI Serial Programming Data Output. During Serial Program Downloading, this pin isused as data output line for the AT90USB82/162.
MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as amaster, this pin is configured as an input regardless of the setting of DDB3. When the SPI isenabled as a slave, the data direction of this pin is controlled by DDB3. When the pin is forced to
be an input, the pull-up can still be controlled by the PORTB3 bit.
PCINT3, Pin Change Interrupt source 3: The PB3 pin can serve as an external interrupt source.
• PDI/MOSI/PCINT2 – Port B, Bit 2
PDI, SPI Serial Programming Data Input. During Serial Program Downloading, this pin is usedas data input line for the AT90USB82/162.
MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as aslave, this pin is configured as an input regardless of the setting of DDB2. When the SPI isenabled as a master, the data direction of this pin is controlled by DDB2. When the pin is forced
to be an input, the pull-up can still be controlled by the PORTB2 bit.
PCINT2, Pin Change Interrupt source 2: The PB2 pin can serve as an external interrupt source.
• SCK/PCINT1 – Port B, Bit 1
SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as aslave, this pin is configured as an input regardless of the setting of DDB1. When the SPI0 isenabled as a master, the data direction of this pin is controlled by DDB1. When the pin is forced
to be an input, the pull-up can still be controlled by the PORTB1 bit. This pin also serves as
Clock for the Serial Programming interface.
PCINT1, Pin Change Interrupt source 1: The PB1 pin can serve as an external interrupt source.
• SS/PCINT0 – Port B, Bit 0
SS: Slave Port Select input. When the SPI is enabled as a slave, this pin is configured as an
input regardless of the setting of DDB0. As a slave, the SPI is activated when this pin is driven
low. When the SPI is enabled as a master, the data direction of this pin is controlled by DDB0.
When the pin is forced to be an input, the pull-up can still be controlled by the PORTB0 bit.
PCINT0, Pin Change Interrupt source 0: The PB0 pin can serve as an external interrupt source.
Table 11-4 and Table 11-5 relate the alternate functions of Port B to the overriding signals
shown in Figure 11-5 on page 72. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the
MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE INPUT.
PCINT0, Pin Change Interrupt source 0: The PB0 pin can serve as an external interrupt source

75
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.Table 11-4 and Table 11-5 relate the alternate functions of Port B to the overriding signals
shown in Figure 11-5 on page 72. SPI MSTR INPUT and SPI SLAVE OUTPUT constitute the
MISO signal, while MOSI is divided into SPI MSTR OUTPUT and SPI SLAVE INPUT..
Table 11-4.

Overriding Signals for Alternate Functions in PB7..PB4

SignalName

PB7/OC0A/OC1C/PCI
NT7

PB6/PCINT6

PB5/PCINT5

PB4/T1/PCINT4

PUOE

0

0

0

0

PUOV

0

0

0

0

DDOE

0

0

0

0

DDOV

0

0

0

0

PVOE

OC0A/OC1C ENABLE

0

0

0

PVOV

OC0A/OC1C

0

0

0

DIEOE

PCINT7 • PCIE0PCINT6 • PCIE0PCINT5 • PCIE0PCINT4 • PCIE0

DIEOV

1

1

1

1

DI

PCINT7 INPUT

PCINT6 INPUT

PCINT5 INPUT

PCINT4 INPUT
T1 INPUT

AIO

–

–

–

–

Table 11-5.

11.3.376

Overriding Signals for Alternate Functions in PB3..PB0

SignalName

PB3/MISO/PCINT3/PD
O

PB2/MOSI/PCINT2/P
DI

PB1/SCK/PCINT1

PB0/SS/PCINT0

PUOE

SPE • MSTR

SPE • MSTR

SPE • MSTR

SPE • MSTRPUOVPORTB3 • PUD

PORTB2 • PUD

PORTB1 • PUD

PORTB0 • PUD

DDOE

SPE • MSTR

SPE • MSTR

SPE • MSTR

SPE • MSTR

DDOV

0

0

0

0

PVOE

SPE • MSTR

SPE • MSTR

SPE • MSTR

0

PVOV

SPI SLAVE OUTPUTSPI MSTR OUTPUTSCK OUTPUT

0

DIEOE

PCINT3 • PCIE0PCINT2 • PCIE0PCINT1 • PCIE0PCINT0 • PCIE0

DIEOV

1

1

1

1

DI

SPI MSTR INPUT
PCINT3 INPUTSPI SLAVE INPUT
PCINT2 INPUTSCK INPUTPCINT1 INPUTSPI SSPCINT0 INPUT

AIO

–

–

–

–

Alternate Functions of Port C
The Port C alternate function is as follows:

AT90USB82/162

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AT90USB82/162
Table 11-6.

Port C Pins Alternate Functions
Port Pin

Alternate Function

PC7

ICP1/INT4/CLKO

PC6

PCINT8/OC1A

PC5

PCINT9/OC1B

PC4

PCINT10--

PC2

PCINT11

PC1

Reset, dW

PC0

XTAL2

The alternate pin configuration is as follows:• ICP1/INT4/CLK0, Bit 7
ICP1, Input Capture pin 1 :The PC7 pin can act as an input capture for Timer/Counter1.
INT4, External Interrupt source 4 : The PC7 pin can serve as an external interrupt source to the
MCU.
CLK0, Clock Output : The PC7 pin can serve as oscillator clock ouput if the feature is enabled byfuse.
• PCINT8/OC1A, Bit 6
PCINT8, Pin Change Interrupt source 8 : The PC6 pin can serve as an external interrupt source.
OC1A, Output Compare Match A output: The PC6 pin can serve as an external output for theTimer/Counter1 Output Compare. The pin has to be configured as an output (DDC6 set “one”) toserve this function. The OC1A pin is also the output pin for the PWM mode timer function.
• PCINT9/OC1B, Bit 5
PCINT9, Pin Change Interrupt source 9: The PC5 pin can serve as an external interrupt source.
OC1B, Output Compare Match B output: The PC5 pin can serve as an external output for theTimer/Counter1 Output Compare. The pin has to be configured as an output (DDC5 set “one”) toserve this function. The OC1B pin is also the output pin for the PWM mode timer function.
• PCINT10, Bit 4
PCINT10, Pin Change Interrupt source 10 : The PC4 pin can serve as an external interrupt
source.
• PCINT11, Bit 2
PCINT11, Pin Change Interrupt source 11 : The PC2 pin can serve as an external interrupt
source.
• Reset/dW, Bit 1
Reset, Reset input. External Reset input is active low and enabled by unprogramming ("1") the
RSTDISBL Fuse. Pullup is activated and output driver and digital input are deactivated when thepin is used as the RESET pin.
77
7707E–AVR–11/08

dW, debugWire channel. When the debugWIRE Enable (DWEN) Fuse is programmed and Lockbits are unprogrammed, the debugWIRE system within the target device is activated. The
RESET port pin is configured as a wired -AND (open-drain) bi-directional I/O pin with pull-up
enabled and becomes the communication gateway between the target and the emulator.
• XTAL2, Bit 0
XTAL2, Oscillator. The PC0 pin can serve as Inverting Output for internal Oscillator amplifier.
Table 11-7 and Table 11-8 relate the alternate functions of Port C to the overriding signals
shown in Figure 11-5 on page 72.
Table 11-7.

Overriding Signals for Alternate Functions in PC7..PC4

SignalName

PC7/ICP1/INT4/CLK0

PC6/PCINT8/OC1
A

PC5/PCINT9/OC1
B

PC4/PCINT10

PUOE

0

0

0

0

PUOV

0

0

0

0

DDOE

0

0

0

0

DDOV

0

0

0

0

PVOE

0

OC1A ENABLE

OC1B ENABLE

0

PVOV

0

OC1A

OC1B

0

DIEOE

INT4 ENABLE

PCINT8 ENABLE

PCINT9 ENABLE

PCINT10 ENABLE

DIEOV

1

1

1

1

DI

INT4 INPUT

PCINT8 INPUT

PCINT9 INPUT

PCINT10 INPUT

AIO

–

–

–

–

Table 11-8.

78

Overriding Signals for Alternate Functions in PC2..PC0

SignalName

PC2/PCINT11

PC1/RESET/dW

PC0/XTAL2

PUOE

0

0

0

PUOV

0

0

0

DDOE

0

0

0

DDOV

0

0

0

PVOE

0

0

0

PVOV

0

0

0

DIEOE

PCINT11 ENABLE

0

0

DIEOV

1

0

0

DI

PCINT11 INPUT

–

–

AIO

–

–

–

AT90USB82/162

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AT90USB82/162
11.3.4

Alternate Functions of Port D
The Port D pins with alternate functions are shown in Table 11-9.
Table 11-9.

Port D Pins Alternate Functions

Port Pin

Alternate Function

PD7

HWB/TO/INT7/CTS

PD6

INT6/RTS

PD5

XCK1/PCINT12 (USART1 External Clock Input/Output)

PD4

INT5

PD3

INT3/TXD1 (External Interrupt3 Input or USART1 Transmit Pin)

PD2

INT2/AIN1/RXD1(External Interrupt2 Input or USART1 Receive Pin)

PD1

INT1/AIN0 (External Interrupt1 Input)

PD0

INT0/OC0B (External Interrupt0 Input)

The alternate pin configuration is as follows:• HWB/TO/INT7/CTS, Bit 7
HWB, Hardware Boot : The PD7 pin can serve as
TO, Timer/Counter0 counter source.
INT7, External Interrupt source 7: The PD7 pin can serve as an external interrupt source to the
MCU.
CTS, USART1 Transmitter Flow Control. This pin can control the transmitter in function of its
state.
• INT6/RTS,Bit 6
INT6, External Interrupt source 6: The PD6 pin can serve as an external interrupt source to the
MCU.
RTS, USART1 Receiver Flow Control. This pin can control the receiver in function of its state.
• XCK1/PCINT12, Bit 5
XCK1, USART1 External Clock : The data direction register DDRD5 controls whether the clock
is output (DDRD5 set) or input (DDRD5 cleared). The XCK1 pin is active only when the USART1
operates in Synchronous Mode.
PCINT12, Pin Change Interrupt source 12: The PD5 pin can serve as an external interrupt
source.
• INT5, Bit 4
INT5, External Interrupt source 5: The PD4 pin can serve as an external interrupt source to the
MCU.
• INT3/TXD1, Bit 3
INT3, External Interrupt source 3: The PD3 pin can serve as an external interrupt source to theMCU.

797707E–AVR–11/08

TXD1, USART1 Transmit Data : When the USART1 Transmitter is enabled, this pin is configured as an ouput regardless of DDRD3.
• INT2/AIN1/RXD1, Bit 2
INT2, External Interrupt source 2: The PD2 pin can serve as an external interrupt source to the
MCU.
AIN1, Analog Comparator Negative input. This pin is directly connected to the negative input of
the Analog Comparator.
RXD1, USART1 Receive Data : When the USART1 Receiver is enabled, this pin is configured
as an input regardless of DDRD2. When the USART forces this pin to be an input, the pull-up
can still be controlled by the PORTD2 bit.
• INT1/AIN0, Bit 1
INT1, External Interrupt source 1: The PD1 pin can serve as an external interrupt source to the
MCU.
AIN0, Analog Comparator Positive input. This pin is directly connected to the positive input of
the Analog Comparator.
• INT0/OC0B, Bit 0
INT0, External Interrupt source 0: The PD0 pin can serve as an external interrupt source to theMCU.
OC0B, Output Compare Match B output: The PD0 pin can serve as an external output for theTimer/Counter0 Output Compare. The pin has to be configured as an output (DDD0 set “one”) toserve this function. The OC0B pin is also the output pin for the PWM mode timer function.
Table 11-10 and Table 11-11 relates the alternate functions of Port D to the overriding signals
shown in Figure 11-5 on page 72.

80

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AT90USB82/162
Table 11-10. Overriding Signals for Alternate Functions PD7..PD4
Signal Name

PD7/T0/INT7/
HBW/CTS

PD6/INT6/RT
S

PD5/XCK/PCINT12

PD4/INT5

PUOE

CTS

RTS

0

0

PUOV

PORTD7 •
PUD

0

0

0

DDOE

CTS

RTS

0

0

DDOV

0

1

0

0

PVOE

0

RTS
OUTPUT
ENABLEXCK OUTPUT ENABLE

0

PVOV

0

RTS
OUTPUTXCK1 OUTPUT

0

DIEOE

INT7/CTSENABLEINT6ENABLEPCINT12 ENABLE

INT5
ENABLE

DIEOV

1

1

1

1

DI

T0 INPUT
INT7 INPUTCTS INPUT

INT6 INPUTXCK INPUTPCINT12 INPUT

INT5 INPUT

AIO

–

–

–

–

Table 11-11. Overriding Signals for Alternate Functions in PD3..PD0(1)Signal Name

PD3/INT3/TXD1

PD2/INT2/RXD1/AIN
1

PD1/INT1/AIN0

PD0/INT0/OC0B

PUOE

TXEN1

RXEN1

0

0

PUOV

0

PORTD2 • PUD

0

0

DDOE

TXEN1

RXEN1

0

0

DDOV

1

0

0

0

PVOE

TXEN1

0

0

OC0B ENABLE

PVOV

TXD1

0

0

OC0B

DIEOE

INT3 ENABLE

INT2 ENABLE
AIN1 ENABLE

INT1 ENABLE
AIN0 ENABLE

INT0 ENABLE

DIEOV

1

AIN1 ENABLE

AIN0 ENABLE

1

DI

INT3 INPUT

INT2 INPUT/RXD1

INT1 INPUT

INT0 INPUTAIO–

AIN1 INPUT

AIN0 INPUT

–

Note:

1. When enabled, the 2-wire Serial Interface enables Slew-Rate controls on the output pins PD0
and PD1. This is not shown in this table. In addition, spike filters are connected between the
AIO outputs shown in the port figure.

81
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11.4
11.4.1

Register Description for I/O-Ports
Port B Data Register – PORTB
Bit

11.4.2

7

6

5

4

3

2

1

0

PORTB7PORTB6PORTB5PORTB4PORTB3PORTB2PORTB1PORTB0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

0

Port B Data Direction Register – DDRB
Bit

11.4.3

7

6

5

4

3

2

1

DDB7

DDB6

DDB5

DDB4

DDB3

DDB2

DDB1

DDB0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

7

6

5

4

3

2

1

0

PINB7

PINB6

PINB5

PINB4

PINB3

PINB2

PINB1

PINB0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

0

7

6

5

4

3

2

1

PORTC7PORTC6PORTC5PORTC4-PORTC2PORTC1PORTC0

Read/Write

R/W

R/W

R/W

R/W

R

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

7

6

5

4

3

2

1

0

DDC7

DDC6

DDC5

DDC4

-

DDC2

DDC1

DDC0

Read/Write

R/W

R/W

R/W

R/W

R

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

0

7

6

5

4

3

2

1

PINC7

PINC6

PINC5

PINC4

-

PINC2

PINC1

PINC0

Read/Write

R/W

R/W

R/W

R/W

R

R/W

R/W

R/W

Initial Value

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

7

6

5

4

3

2

1

0

PORTD7

PORTD6

PORTD5PORTD4PORTD3PORTD2PORTD1PORTD0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

0

PORTD

Port D Data Direction Register – DDRD
Bit

82

PINC

Port D Data Register – PORTD
Bit

11.4.8DDRC

Port C Input Pins Address – PINC
Bit

11.4.7PORTC

Port C Data Direction Register – DDRC
Bit

11.4.6PINB

Port C Data Register – PORTC
Bit

11.4.5DDRB

Port B Input Pins Address – PINB
Bit

11.4.4

PORTB

7

6

5

4

3

2

1

DDD7

DDD6

DDD5

DDD4

DDD3

DDD2

DDD1

DDD0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

AT90USB82/162

DDRD

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AT90USB82/162
11.4.9Port D Input Pins Address – PIND
Bit

7

6

5

4

3

2

1

0

PIND7

PIND6

PIND5

PIND4

PIND3

PIND2

PIND1

PIND0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

PIND

83
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12. External Interrupts
The External Interrupts are triggered by the INT7:0 pin or any of the PCINT12..0 pins. Observe
that, if enabled, the interrupts will trigger even if the INT7:0 or PCINT12..0 pins are configured as
outputs. This feature provides a way of generating a software interrupt.
The Pin change interrupt PCI0 will trigger if any enabled PCINT7:0 pin toggles. PCMSK0 Register control which pins contribute to the pin change interrupts. The Pin change interrupt PCI1 will
trigger if any enabled PCINT12:8 pin toggles. PCMSK1 Register control which pins contribute to
the pin change interrupts. Pin change interrupts on PCINT12 ..0 are detected asynchronously.
This implies that these interrupts can be used for waking the part also from sleep modes otherthan Idle mode.
The External Interrupts can be triggered by a falling or rising edge or a low level. This is set up
as indicated in the specification for the External Interrupt Control Registers – EICRA (INT3:0)
and EICRB (INT7:4). When the external interrupt is enabled and is configured as level triggered,
the interrupt will trigger as long as the pin is held low. Note that recognition of falling or risingedge interrupts on INT7:4 requires the presence of an I/O clock, described in “System Clock andClock Options” on page 25. Low level interrupts and the edge interrupt on INT3:0 are detectedasynchronously. This implies that these interrupts can be used for waking the part also fromsleep modes other than Idle mode. The I/O clock is halted in all sleep modes except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down, the required levelmust be held long enough for the MCU to complete the wake-up to trigger the level interrupt. If
the level disappears before the end of the Start-up Time, the MCU will still wake up, but no interrupt will be generated. The start-up time is defined by the SUT and CKSEL Fuses as describedin “System Clock and Clock Options” on page 25.
12.0.1

External Interrupt Control Register A – EICRAThe External Interrupt Control Register A contains control bits for interrupt sense control.
Bit

7

6

5

4

3

2

1

ISC31

ISC30

ISC21

ISC20

ISC11

ISC10

ISC01

0
ISC00

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

EICRA

• Bits 7..0 – ISC31, ISC30 – ISC00, ISC00: External Interrupt 3 - 0 Sense Control Bits
The External Interrupts 3 - 0 are activated by the external pins INT3:0 if the SREG I-flag and thecorresponding interrupt mask in the EIMSK is set. The level and edges on the external pins that
activate the interrupts are defined in Table 12-1. Edges on INT3..INT0 are registered asynchronously. Pulses on INT3:0 pins wider than the minimum pulse width given in Table 12-2 will
generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If low levelinterrupt is selected, the low level must be held until the completion of the currently executing
instruction to generate an interrupt. If enabled, a level triggered interrupt will generate an interrupt request as long as the pin is held low. When changing the ISCn bit, an interrupt can occur.
Therefore, it is recommended to first disable INTn by clearing its Interrupt Enable bit in the
EIMSK Register. Then, the ISCn bit can be changed. Finally, the INTn interrupt flag should becleared by writing a logical one to its Interrupt Flag bit (INTFn) in the EIFR Register before theinterrupt is re-enabled.

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Interrupt Sense Control(1)Table 12-1.
ISCn1

ISCn0

0

0

The low level of INTn generates an interrupt request.

01

Any edge of INTn generates asynchronously an interrupt request.

1

0

The falling edge of INTn generates asynchronously an interrupt request.

1

1

The rising edge of INTn generates asynchronously an interrupt request.

Note:

1. n = 3, 2, 1or 0.
When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its Interrupt
Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the bits are changed.

Table 12-2.
SymbolAsynchronous External Interrupt Characteristics
Parameter

ConditionMin

Minimum pulse width for asynchronous
external interrupt

tINT

12.0.2

Description

Typ

Max

Units

50

ns

External Interrupt Control Register B – EICRB
Bit

7

6

5

4

3

2

1

0

ISC71

ISC70

ISC61

ISC60

ISC51

ISC50

ISC41

ISC40

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

EICRB

• Bits 7..0 – ISC71, ISC70 - ISC41, ISC40: External Interrupt 7 - 4 Sense Control Bits
The External Interrupts 7 - 4 are activated by the external pins INT7:4 if the SREG I-flag and thecorresponding interrupt mask in the EIMSK is set. The level and edges on the external pins that
activate the interrupts are defined in Table 12-3. The value on the INT7:4 pins are sampled
before detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one
clock period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. Observe that CPU clock frequency can be lower than the XTAL frequency if the XTAL
divider is enabled. If low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. If enabled, a level triggeredinterrupt will generate an interrupt request as long as the pin is held low.
Interrupt Sense Control(1)Table 12-3.
ISCn1

ISCn0

0

0

The low level of INTn generates an interrupt request.

0

1

Any logical change on INTn generates an interrupt request

1

0

The falling edge between two samples of INTn generates an interrupt request.

1

1

The rising edge between two samples of INTn generates an interrupt request.

Note:

Description

1. n = 7, 6, 5 or 4.
When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its Interrupt
Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the bits are changed.

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External Interrupt Mask Register – EIMSK
Bit

7

6

5

4

3

2

1

INT7

INT6

INT5

INT4

INT3

INT2

INT1

0
IINT0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

EIMSK

• Bits 7..0 – INT7 – INT0: External Interrupt Request 7 - 0 Enable
When an INT7 – INT0 bit is written to one and the I-bit in the Status Register (SREG) is set(one), the corresponding external pin interrupt is enabled. The Interrupt Sense Control bits in theExternal Interrupt Control Registers – EICRA and EICRB – defines whether the external interrupt is activated on rising or falling edge or level sensed. Activity on any of these pins will trigger
an interrupt request even if the pin is enabled as an output. This provides a way of generating asoftware interrupt.
12.0.4External Interrupt Flag Register – EIFR
Bit

7

6

5

4

3

2

1

0

INTF7

INTF6

INTF5

INTF4

INTF3

INTF2

INTF1

INTF0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

EIFR

• Bits 7..0 – INTF7 - INTF0: External Interrupt Flags 7 - 0
When an edge or logic change on the INT7:0 pin triggers an interrupt request, INTF7:0 becomesset (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT7:0 in EIMSK, areset (one), the MCU will jump to the interrupt vector. The flag is cleared when the interrupt routine
is executed. Alternatively, the flag can be cleared by writing a logical one to it. These flags arealways cleared when INT7:0 are configured as level interrupt. Note that when entering sleep
mode with the INT3:0 interrupts disabled, the input buffers on these pins will be disabled. Thismay cause a logic change in internal signals which will set the INTF3:0 flags. See “Digital Input
Enable and Sleep Modes” on page 71 for more information.
12.0.5

Pin Change Interrupt Control Register - PCICR
Bit

7

6

5

4

3

2

1

-

-

–

–

–

–

PCIE1

0
PCIE0

Read/Write

R

R

R

R

R

R

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

PCICR

• Bit 1..0 – PCIE1- PCIE0: Pin Change Interrupt Enable 1-0
When the PCIE1/0 bit is set (one) and the I-bit in the Status Register (SREG) is set (one),
Pin Change interrupt 1/0 is enabled. Any change on any enabled PCINT12..8/7..0 pin willcause an interrupt. The corresponding interrupt of Pin Change Interrupt Request is executed from the PCI1/0 Interrupt Vector. PCINT12..8/7..0 pins are enabled individually by the
PCMSK1/0 Register.
12.0.6

Pin Change Interrupt Flag Register – PCIFR
Bit

7

6

5

4

3

2

1

-

-

–

–

–

–

PCIF1

0
PCIF0

Read/Write

R

R

R

R

R

R

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

PCIFR

• Bit 1..0 – PCIF1- PCIF0: Pin Change Interrupt Flag 1-0

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When a logic change on any PCINT12..8/7..0 pin triggers an interrupt request, PCIF1/0
becomes set (one). If the I-bit in SREG and the PCIE1/0 bit in PCICR are set (one), the MCU will
jump to the corresponding Interrupt Vector. The flag is cleared when the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical one to it.
12.0.7

Pin Change Mask Register 0 – PCMSK0
Bit

7

6

5

4

3

2

1

0

PCINT7PCINT6

PCINT5

PCINT4

PCINT3

PCINT2

PCINT1

PCINT0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

PCMSK0• Bit 7..0 – PCINT7..0: Pin Change Enable Mask 7..0
Each PCINT7..0 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT7..0 is set and the PCIE0 bit in PCICR is set, pin change interrupt is enabled on thecorresponding I/O pin. If PCINT7..0 is cleared, pin change interrupt on the corresponding I/O pin
is disabled.
12.0.8

Pin Change Mask Register 1– PCMSK1
Bit

7

6

5

4

3

2

1

-

-

-

PCINT12PCINT11

PCINT10

PCINT90
PCINT8Read/Write

R

R

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

PCMSK1• Bit 4..0 – PCINT12..8: Pin Change Enable Mask 12..8
Each PCINT12..8 bit selects whether pin change interrupt is enabled on the corresponding I/O
pin. If PCINT12..8 is set and the PCIE1 bit in PCICR is set, pin change interrupt is enabled on
the corresponding I/O pin. If PCINT12..8 is cleared, pin change interrupt on the corresponding
I/O pin is disabled.

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13. Timer/Counter0 and Timer/Counter1 Prescalers
Timer/Counter0 and 1 share the same prescaler module, but the Timer/Counters can have different prescaler settings. The description below applies to all Timer/Counters. Tn is used as a
general name, n = 0 or 1.
13.0.1

Internal Clock Source
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as aclock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64, fCLK_I/O/256, or
fCLK_I/O/1024.

13.0.2Prescaler Reset
The prescaler is free running, i.e., operates independently of the Clock Select logic of theTimer/Counter, and it is shared by the Timer/Counter Tn. Since the prescaler is not affected by
the Timer/Counter’s clock select, the state of the prescaler will have implications for situations
where a prescaled clock is used. One example of prescaling artifacts occurs when the timer isenabled and clocked by the prescaler (6 > CSn2:0 > 1). The number of system clock cycles fromwhen the timer is enabled to the first count occurs can be from 1 to N+1 system clock cycles,
where N equals the prescaler divisor (8, 64, 256, or 1024).
It is possible to use the prescaler reset for synchronizing the Timer/Counter to program execution. However, care must be taken if the other Timer/Counter that shares the same prescaleralso uses prescaling. A prescaler reset will affect the prescaler period for all Timer/Counters it isconnected to.

13.0.3External Clock Source
An external clock source applied to the Tn pin can be used as Timer/Counter clock (clkTn). The
Tn pin is sampled once every system clock cycle by the pin synchronization logic. The synchronized (sampled) signal is then passed through the edge detector. Figure 13-1 shows a functional
equivalent block diagram of the Tn synchronization and edge detector logic. The registers areclocked at the positive edge of the internal system clock (clkI/O). The latch is transparent in thehigh period of the internal system clock.
The edge detector generates one clkTn pulse for each positive (CSn2:0 = 7) or negative (CSn2:0= 6) edge it detects.
Figure 13-1. Tn/T0 Pin Sampling
Tn

D

Q

D

Q

D

Tn_sync(To ClockSelect Logic)Q

LE
clk I/O
Synchronization

Edge Detector

The synchronization and edge detector logic introduces a delay of 2.5 to 3.5 system clock cycles
from an edge has been applied to the Tn pin to the counter is updated.
Enabling and disabling of the clock input must be done when Tn has been stable for at least one
system clock cycle, otherwise it is a risk that a false Timer/Counter clock pulse is generated.
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Each half period of the external clock applied must be longer than one system clock cycle toensure correct sampling. The external clock must be guaranteed to have less than half the system clock frequency (fExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses
sampling, the maximum frequency of an external clock it can detect is half the sampling frequency (Nyquist sampling theorem). However, due to variation of the system clock frequency
and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it isrecommended that maximum frequency of an external clock source is less than fclk_I/O/2.5.
An external clock source can not be prescaled.
Figure 13-2. Prescaler for synchronous Timer/Counters
clk I/O

Clear

PSR10

Tn

Synchronization

Tn

Synchronization

CSn0

CSn0

CSn1

CSn1

CSn2

CSn2

TIMER/COUNTERn CLOCK SOURCE
clkTn

13.0.4

TIMER/COUNTERn CLOCK SOURCE
clkTn

General Timer/Counter Control Register – GTCCR
Bit

7

6

5

4

3

2

1

0

TSM

–

–

–

–

–

-

PSRSY
NC

Read/Write

R/W

R

R

R

R

R

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

GTCCR

• Bit 7 – TSM: Timer/Counter Synchronization Mode
Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, thevalue that is written to the PSRASY and PSRSYNC bits is kept, hence keeping the corresponding prescaler reset signals asserted. This ensures that the corresponding Timer/Counters arehalted and can be configured to the same value without the risk of one of them advancing duringconfiguration. When the TSM bit is written to zero, the PSRASY and PSRSYNC bits are clearedby hardware, and the Timer/Counters start counting simultaneously.
• Bit 0 – PSRSYNC: Prescaler Reset for Synchronous Timer/Counters
When this bit is one, Timer/Counter0 and Timer/Counter1, Timer/Counter3, Timer/Counter4 andTimer/Counter5 prescaler will be Reset. This bit is normally cleared immediately by hardware,
except if the TSM bit is set. Note that Timer/Counter0 and Timer/Counter1 share the same prescaler and a reset of this prescaler will affect all timers.

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14. 8-bit Timer/Counter0 with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent Output
Compare Units, and with PWM support. It allows accurate program execution timing (event management) and wave generation. The main features are:
• Two Independent Output Compare Units• Double Buffered Output Compare Registers• Clear Timer on Compare Match (Auto Reload)• Glitch Free, Phase Correct Pulse Width Modulator (PWM)• Variable PWM Period• Frequency Generator• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)

14.1

Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 14-1. For the actual
placement of I/O pins, refer to “Pinout AT90USB82/162” on page 3. CPU accessible I/O Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit
locations are listed in the “8-bit Timer/Counter Register Description” on page 100.
Figure 14-1. 8-bit Timer/Counter Block Diagram
Count
Clear
Direction

TOVn(Int.Req.)
Control Logic

clkTn

Clock SelectEdge
Detector

TOP

Tn

BOTTOM( From Prescaler )Timer/Counter
TCNTn

=

=0
OCnA
(Int.Req.)
Waveform
Generation

=

OCnA

DATA BUS

OCRnA
Fixed
TOP
Value

Waveform
Generation

=

OCnB

OCRnB

TCCRnA

14.1.1

OCnB(Int.Req.)

TCCRnB

Registers
The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are 8-bit
registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in theTimer Interrupt Flag Register (TIFR0). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 pin. The Clock Select logic block controls which clock source and edge the Timer/Counteruses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the Clock Select logic is referred to as the timer clock (clkT0).

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The double buffered Output Compare Registers (OCR0A and OCR0B) are compared with theTimer/Counter value at all times. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare pins (OC0A andOC0B). See “Output Compare Unit” on page 92. for details. The Compare Match event will also
set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Output Compareinterrupt request.
14.1.2

Definitions
Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Compare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register orbit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
The definitions in Table 14-1 are also used extensively throughout the document.

14.2

Table 14-1.

Definitions

BOTTOM

The counter reaches the BOTTOM when it becomes 0x00.

MAX

The counter reaches its MAXimum when it becomes 0xFF (decimal 255).

TOP

The counter reaches the TOP when it becomes equal to the highest value in the
count sequence. The TOP value can be assigned to be the fixed value 0xFF
(MAX) or the value stored in the OCR0A Register. The assignment is dependent on the mode of operation.

Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0B). For details on clock sources and prescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 88.

14.3Counter Unit
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. Figure14-2 shows a block diagram of the counter and its surroundings.
Figure 14-2. Counter Unit Block Diagram
TOVn(Int.Req.)DATA BUS

Clock Select
count
clear

TCNTn

direction

Control Logic

clkTn

Edge
Detector

Tn( From Prescaler )bottomtop

Signal description (internal signals):count

Increment or decrement TCNT0 by 1.

direction

Select between increment and decrement.
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clearClear TCNT0 (set all bits to zero).

clkTnTimer/Counter clock, referred to as clkT0 in the following.

top

Signalize that TCNT0 has reached maximum value.

bottomSignalize that TCNT0 has reached minimum value (zero).

Depending of the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkT0). clkT0 can be generated from an external or internal clock source,
selected by the Clock Select bits (CS02:0). When no clock source is selected (CS02:0 = 0) the
timer is stopped. However, the TCNT0 value can be accessed by the CPU, regardless ofwhether clkT0 is present or not. A CPU write overrides (has priority over) all counter clear orcount operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in
the Timer/Counter Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter
Control Register B (TCCR0B). There are close connections between how the counter behaves(counts) and how waveforms are generated on the Output Compare outputs OC0A and OC0B.
For more details about advanced counting sequences and waveform generation, see “Modes ofOperation” on page 95.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by
the WGM02:0 bits. TOV0 can be used for generating a CPU interrupt.

14.4

Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers(OCR0A and OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals amatch. A match will set the Output Compare Flag (OCF0A or OCF0B) at the next timer clock
cycle. If the corresponding interrupt is enabled, the Output Compare Flag generates an Output
Compare interrupt. The Output Compare Flag is automatically cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writing a logical one to its I/O bit
location. The Waveform Generator uses the match signal to generate an output according tooperating mode set by the WGM02:0 bits and Compare Output mode (COM0x1:0) bits. The max
and bottom signals are used by the Waveform Generator for handling the special cases of theextreme values in some modes of operation (“Modes of Operation” on page 95).
Figure 14-3 shows a block diagram of the Output Compare unit.

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Figure 14-3. Output Compare Unit, Block Diagram

DATA BUS

OCRnx

TCNTn

= (8-bit Comparator )OCFnx (Int.Req.)
topbottomWaveform Generator

OCnx

FOCn

WGMn1:0

COMnX1:0

The OCR0x Registers are double buffered when using any of the Pulse Width Modulation(PWM) modes. For the normal and Clear Timer on Compare (CTC) modes of operation, the double buffering is disabled. The double buffering synchronizes the update of the OCR0x Compare
Registers to either top or bottom of the counting sequence. The synchronization prevents theoccurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCR0x Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCR0x Buffer Register, and if double buffering is disabled the CPU will access the OCR0x directly.
14.4.1Force Output Compare
In non-PWM waveform generation modes, the match output of the comparator can be forced bywriting a one to the Force Output Compare (FOC0x) bit. Forcing Compare Match will not set the
OCF0x Flag or reload/clear the timer, but the OC0x pin will be updated as if a real Compare
Match had occurred (the COM0x1:0 bits settings define whether the OC0x pin is set, cleared or
toggled).

14.4.2Compare Match Blocking by TCNT0 Write
All CPU write operations to the TCNT0 Register will block any Compare Match that occur in thenext timer clock cycle, even when the timer is stopped. This feature allows OCR0x to be initialized to the same value as TCNT0 without triggering an interrupt when the Timer/Counter clock is
enabled.

14.4.3Using the Output Compare Unit
Since writing TCNT0 in any mode of operation will block all Compare Matches for one timer
clock cycle, there are risks involved when changing TCNT0 when using the Output Compare
Unit, independently of whether the Timer/Counter is running or not. If the value written to TCNT0
equals the OCR0x value, the Compare Match will be missed, resulting in incorrect waveform

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generation. Similarly, do not write the TCNT0 value equal to BOTTOM when the counter isdown-counting.
The setup of the OC0x should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OC0x value is to use the Force Output Compare (FOC0x) strobe bits in Normal mode. The OC0x Registers keep their values even whenchanging between Waveform Generation modes.
Be aware that the COM0x1:0 bits are not double buffered together with the compare value.
Changing the COM0x1:0 bits will take effect immediately.

14.5

Compare Match Output Unit
The Compare Output mode (COM0x1:0) bits have two functions. The Waveform Generator uses
the COM0x1:0 bits for defining the Output Compare (OC0x) state at the next Compare Match.
Also, the COM0x1:0 bits control the OC0x pin output source. Figure 14-4 shows a simplified
schematic of the logic affected by the COM0x1:0 bit setting. The I/O Registers, I/O bits, and I/Opins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers(DDR and PORT) that are affected by the COM0x1:0 bits are shown. When referring to theOC0x state, the reference is for the internal OC0x Register, not the OC0x pin. If a system reset
occur, the OC0x Register is reset to “0”.
Figure 14-4. Compare Match Output Unit, Schematic

COMnx1
COMnx0
FOCn

Waveform
Generator

D

Q
1

OCnx

DATA BUS

D

0

OCnx
Pin

Q

PORT
D

Q

DDR
clk I/O

The general I/O port function is overridden by the Output Compare (OC0x) from the Waveform
Generator if either of the COM0x1:0 bits are set. However, the OC0x pin direction (input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OC0x pin (DDR_OC0x) must be set as output before the OC0x value is visible on the pin. The port override function is independent of the Waveform Generation mode.
The design of the Output Compare pin logic allows initialization of the OC0x state before the output is enabled. Note that some COM0x1:0 bit settings are reserved for certain modes ofoperation. See “8-bit Timer/Counter Register Description” on page 100.

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14.5.1Compare Output Mode and Waveform Generation
The Waveform Generator uses the COM0x1:0 bits differently in Normal, CTC, and PWM modes.
For all modes, setting the COM0x1:0 = 0 tells the Waveform Generator that no action on the
OC0x Register is to be performed on the next Compare Match. For compare output actions in
the non-PWM modes refer to Table 14-2 on page 101. For fast PWM mode, refer to Table 14-3
on page 101, and for phase correct PWM refer to Table 14-4 on page 101.
A change of the COM0x1:0 bits state will have effect at the first Compare Match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOC0x strobe bits.

14.6

Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, isdefined by the combination of the Waveform Generation mode (WGM02:0) and Compare Output
mode (COM0x1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COM0x1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COM0x1:0 bits control whether the output should be set, cleared, or toggled at a Compare
Match (See “Compare Match Output Unit” on page 94.).
For detailed timing information see “Timer/Counter Timing Diagrams” on page 99.

14.6.1

Normal Mode
The simplest mode of operation is the Normal mode (WGM02:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 8-bit value (TOP = 0xFF) and then restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0) will be set in the sametimer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this case behaves like a ninth
bit, except that it is only set, not cleared. However, combined with the timer overflow interrupt
that automatically clears the TOV0 Flag, the timer resolution can be increased by software.
There are no special cases to consider in the Normal mode, a new counter value can be written
anytime.
The Output Compare Unit can be used to generate interrupts at some given time. Using the Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.

14.6.2

Clear Timer on Compare Match (CTC) ModeIn Clear Timer on Compare or CTC mode (WGM02:0 = 2), the OCR0A Register is used tomanipulate the counter resolution. In CTC mode the counter is cleared to zero when the countervalue (TCNT0) matches the OCR0A. The OCR0A defines the top value for the counter, hence
also its resolution. This mode allows greater control of the Compare Match output frequency. It
also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 14-5. The counter value (TCNT0)
increases until a Compare Match occurs between TCNT0 and OCR0A, and then counter(TCNT0) is cleared.

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Figure 14-5. CTC Mode, Timing Diagram
OCnx Interrupt Flag Set

TCNTn
OCn
(Toggle)Period(COMnx1:0 = 1)
1

2

3

4

An interrupt can be generated each time the counter value reaches the TOP value by using the
OCF0A Flag. If the interrupt is enabled, the interrupt handler routine can be used for updating
the TOP value. However, changing TOP to a value close to BOTTOM when the counter is running with none or a low prescaler value must be done with care since the CTC mode does nothave the double buffering feature. If the new value written to OCR0A is lower than the current
value of TCNT0, the counter will miss the Compare Match. The counter will then have to count to
its maximum value (0xFF) and wrap around starting at 0x00 before the Compare Match canoccur.
For generating a waveform output in CTC mode, the OC0A output can be set to toggle its logicallevel on each Compare Match by setting the Compare Output mode bits to toggle mode
(COM0A1:0 = 1). The OC0A value will not be visible on the port pin unless the data direction forthe pin is set to output. The waveform generated will have a maximum frequency of f OC0 =fclk_I/O/2 when OCR0A is set to zero (0x00). The waveform frequency is defined by the following
equation:f clk_I/O
f OCnx = -------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnx )The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOV0 Flag is set in the same timer clock cycle that thecounter counts from MAX to 0x00.
14.6.3

Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGM02:0 = 3 or 7) provides a high frequency PWM waveform generation option. The fast PWM differs from the other PWM option by
its single-slope operation. The counter counts from BOTTOM to TOP then restarts from BOTTOM. TOP is defined as 0xFF when WGM2:0 = 3, and OCR0A when WGM2:0 = 7. In noninverting Compare Output mode, the Output Compare (OC0x) is cleared on the Compare Match
between TCNT0 and OCR0x, and set at BOTTOM. In inverting Compare Output mode, the output is set on Compare Match and cleared at BOTTOM. Due to the single-slope operation, theoperating frequency of the fast PWM mode can be twice as high as the phase correct PWM
mode that use dual-slope operation. This high frequency makes the fast PWM mode well suitedfor power regulation, rectification, and DAC applications. High frequency allows physically small
sized external components (coils, capacitors), and therefore reduces total system cost.
In fast PWM mode, the counter is incremented until the counter value matches the TOP value.
The counter is then cleared at the following timer clock cycle. The timing diagram for the fast

96

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AT90USB82/162
PWM mode is shown in Figure 14-6. The TCNT0 value is in the timing diagram shown as a histogram for illustrating the single-slope operation. The diagram includes non-inverted andinverted PWM outputs. The small horizontal line marks on the TCNT0 slopes represent Compare Matches between OCR0x and TCNT0.
Figure 14-6. Fast PWM Mode, Timing Diagram
OCRnx Interrupt Flag Set

OCRnx Update and
TOVn Interrupt Flag Set

TCNTn

OCnx

(COMnx1:0 = 2)

OCnx

(COMnx1:0 = 3)

Period

1

2

3

4

5

6

7

The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches TOP. If the interrupt is enabled, the interrupt handler routine can be used for updating the compare value.
In fast PWM mode, the compare unit allows generation of PWM waveforms on the OC0x pins.
Setting the COM0x1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COM0x1:0 to three: Setting the COM0A1:0 bits to one allows
the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is not available
for the OC0B pin (See Table 14-3 on page 101). The actual OC0x value will only be visible on
the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by setting (or clearing) the OC0x Register at the Compare Match between OCR0x and
TCNT0, and clearing (or setting) the OC0x Register at the timer clock cycle the counter iscleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = -----------------N ⋅ 256
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCR0A is set equal to BOTTOM, the output will
be a narrow spike for each MAX+1 timer clock cycle. Setting the OCR0A equal to MAX will resultin a constantly high or low output (depending on the polarity of the output set by the COM0A1:0
bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OC0x to toggle its logical level on each Compare Match (COM0x1:0 = 1). The waveformgenerated will have a maximum frequency of fOC0 = fclk_I/O/2 when OCR0A is set to zero. This

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feature is similar to the OC0A toggle in CTC mode, except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
14.6.4Phase Correct PWM Mode
The phase correct PWM mode (WGM02:0 = 1 or 5) provides a high resolution phase correct
PWM waveform generation option. The phase correct PWM mode is based on a dual-slope
operation. The counter counts repeatedly from BOTTOM to TOP and then from TOP to BOTTOM. TOP is defined as 0xFF when WGM2:0 = 1, and OCR0A when WGM2:0 = 5. In noninverting Compare Output mode, the Output Compare (OC0x) is cleared on the Compare Match
between TCNT0 and OCR0x while upcounting, and set on the Compare Match while downcounting. In inverting Output Compare mode, the operation is inverted. The dual-slope operation
has lower maximum operation frequency than single slope operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes are preferred for motor control
applications.
In phase correct PWM mode the counter is incremented until the counter value matches TOP.
When the counter reaches TOP, it changes the count direction. The TCNT0 value will be equal
to TOP for one timer clock cycle. The timing diagram for the phase correct PWM mode is shown
on Figure 14-7. The TCNT0 value is in the timing diagram shown as a histogram for illustrating
the dual-slope operation. The diagram includes non-inverted and inverted PWM outputs. The
small horizontal line marks on the TCNT0 slopes represent Compare Matches between OCR0x
and TCNT0.
Figure 14-7. Phase Correct PWM Mode, Timing Diagram
OCnx Interrupt Flag Set

OCRnx Update

TOVn Interrupt Flag Set

TCNTn

OCnx

(COMnx1:0 = 2)

OCnx

(COMnx1:0 = 3)

Period1

2

3

The Timer/Counter Overflow Flag (TOV0) is set each time the counter reaches BOTTOM. The
Interrupt Flag can be used to generate an interrupt each time the counter reaches the BOTTOM
value.
In phase correct PWM mode, the compare unit allows generation of PWM waveforms on the
OC0x pins. Setting the COM0x1:0 bits to two will produce a non-inverted PWM. An inverted
PWM output can be generated by setting the COM0x1:0 to three: Setting the COM0A0 bits to98

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AT90USB82/162
one allows the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is
not available for the OC0B pin (See Table 14-4 on page 101). The actual OC0x value will only
be visible on the port pin if the data direction for the port pin is set as output. The PWM waveform is generated by clearing (or setting) the OC0x Register at the Compare Match between
OCR0x and TCNT0 when the counter increments, and setting (or clearing) the OC0x Register at
Compare Match between OCR0x and TCNT0 when the counter decrements. The PWM frequency for the output when using phase correct PWM can be calculated by the following
equation:f clk_I/O
f OCnxPCPWM = -----------------N ⋅ 510
The N variable represents the prescale factor (1, 8, 64, 256, or 1024).
The extreme values for the OCR0A Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCR0A is set equal to BOTTOM, theoutput will be continuously low and if set equal to MAX the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values.
At the very start of period 2 in Figure 14-7 OCnx has a transition from high to low even though
there is no Compare Match. The point of this transition is to guarantee symmetry around BOTTOM. There are two cases that give a transition without Compare Match.
• OCR0A changes its value from MAX, like in Figure 14-7. When the OCR0A value is MAX theOCn pin value is the same as the result of a down-counting Compare Match. To ensure
symmetry around BOTTOM the OCn value at MAX must correspond to the result of an upcounting Compare Match.
• The timer starts counting from a value higher than the one in OCR0A, and for that reason
misses the Compare Match and hence the OCn change that would have happened on theway up.

14.7

Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore shown as aclock enable signal in the following figures. The figures include information on when Interrupt
Flags are set. Figure 14-8 contains timing data for basic Timer/Counter operation. The figure
shows the count sequence close to the MAX value in all modes other than phase correct PWM
mode.
Figure 14-8. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn(clkI/O /1)

TCNTn

MAX - 1MAX

BOTTOM

BOTTOM + 1

TOVn

Figure 14-9 shows the same timing data, but with the prescaler enabled.

997707E–AVR–11/08

Figure 14-9. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn(clkI/O /8)

TCNTn

MAX - 1MAX

BOTTOM

BOTTOM + 1

TOVn

Figure 14-10 shows the setting of OCF0B in all modes and OCF0A in all modes except CTC
mode and PWM mode, where OCR0A is TOP.
Figure 14-10. Timer/Counter Timing Diagram, Setting of OCF0x, with Prescaler (fclk_I/O/8)
clkI/O
clkTn(clkI/O /8)

TCNTn

OCRnx - 1

OCRnx

OCRnx

OCRnx + 1

OCRnx + 2

OCRnx Value

OCFnx

Figure 14-11 shows the setting of OCF0A and the clearing of TCNT0 in CTC mode and fast
PWM mode where OCR0A is TOP.
Figure 14-11. Timer/Counter Timing Diagram, Clear Timer on Compare Match mode, with Prescaler (fclk_I/O/8)
clkI/O
clkTn(clkI/O /8)

TCNTn
(CTC)

TOP - 1

TOP

OCRnx

BOTTOM

BOTTOM + 1

TOP

OCFnx

14.8

8-bit Timer/Counter Register Description

14.8.1

Timer/Counter Control Register A – TCCR0A
Bit
Read/Write

100

AT90USB82/162

7

6

5

4

3

2

1

COM0A1

COM0A0COM0B1COM0B0

–

–

WGM01

0
WGM00

R/W

R/W

R/W

R/W

R

R

R/W

R/W

TCCR0A

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AT90USB82/162
Initial Value

0

0

0

0

0

0

0

0

• Bits 7:6 – COM01A:0: Compare Match Output A Mode
These bits control the Output Compare pin (OC0A) behavior. If one or both of the COM0A1:0
bits are set, the OC0A output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0A pin
must be set in order to enable the output driver.
When OC0A is connected to the pin, the function of the COM0A1:0 bits depends on the
WGM02:0 bit setting. Table 14-2 shows the COM0A1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 14-2.

Compare Output Mode, non-PWM Mode

COM0A1

COM0A0Description00Normal port operation, OC0A disconnected.

0

1

Toggle OC0A on Compare Match

1

0

Clear OC0A on Compare Match

1

1

Set OC0A on Compare Match

Table 14-3 shows the COM0A1:0 bit functionality when the WGM01:0 bits are set to fast PWM
mode.
Table 14-3.

Compare Output Mode, Fast PWM Mode(1)COM0A1

COM0A000Normal port operation, OC0A disconnected.

0

1

WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.

10

Clear OC0A on Compare Match, set OC0A at TOP

1

1

Set OC0A on Compare Match, clear OC0A at TOP

Note:

Description

1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 96
for more details.

Table 14-4 shows the COM0A1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 14-4.

Compare Output Mode, Phase Correct PWM Mode(1)COM0A1

COM0A0Description00Normal port operation, OC0A disconnected.

0

1

WGM02 = 0: Normal Port Operation, OC0A Disconnected.
WGM02 = 1: Toggle OC0A on Compare Match.

10

Clear OC0A on Compare Match when up-counting. Set OC0A on
Compare Match when down-counting.

1

1

Set OC0A on Compare Match when up-counting. Clear OC0A on
Compare Match when down-counting.

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Note:

1. A special case occurs when OCR0A equals TOP and COM0A1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” onpage 98 for more details.

• Bits 5:4 – COM0B1:0: Compare Match Output B Mode
These bits control the Output Compare pin (OC0B) behavior. If one or both of the COM0B1:0
bits are set, the OC0B output overrides the normal port functionality of the I/O pin it is connected
to. However, note that the Data Direction Register (DDR) bit corresponding to the OC0B pin
must be set in order to enable the output driver.
When OC0B is connected to the pin, the function of the COM0B1:0 bits depends on the
WGM02:0 bit setting. Table 14-2 shows the COM0A1:0 bit functionality when the WGM02:0 bits
are set to a normal or CTC mode (non-PWM).
Table 14-5.

Compare Output Mode, non-PWM Mode

COM01

COM00

Description00Normal port operation, OC0B disconnected.

0

1

Toggle OC0B on Compare Match

1

0

Clear OC0B on Compare Match

1

1

Set OC0B on Compare Match

Table 14-3 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to fast PWM
mode.
Table 14-6.

Compare Output Mode, Fast PWM Mode(1)

COM01

COM00

0

0

Normal port operation, OC0B disconnected.

01

Reserved

10

Clear OC0B on Compare Match, set OC0B at TOP

1

1

Set OC0B on Compare Match, clear OC0B at TOP

Note:

Description

1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Fast PWM Mode” on page 96
for more details.

Table 14-4 shows the COM0B1:0 bit functionality when the WGM02:0 bits are set to phase correct PWM mode.
Table 14-7.

102

Compare Output Mode, Phase Correct PWM Mode(1)COM0A1

COM0A000Normal port operation, OC0B disconnected.

01

Reserved

10

Clear OC0B on Compare Match when up-counting. Set OC0B on
Compare Match when down-counting.

1

1

Set OC0B on Compare Match when up-counting. Clear OC0B on
Compare Match when down-counting.

AT90USB82/162

Description

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AT90USB82/162
Note:

1. A special case occurs when OCR0B equals TOP and COM0B1 is set. In this case, the Compare Match is ignored, but the set or clear is done at TOP. See “Phase Correct PWM Mode” onpage 98 for more details.

• Bits 3, 2 – Res: Reserved Bits
These bits are reserved bits in the AT90USB82/162 and will always read as zero.
• Bits 1:0 – WGM01:0: Waveform Generation Mode
Combined with the WGM02 bit found in the TCCR0B Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 14-8. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare Match (CTC) mode, and two types ofPulse Width Modulation (PWM) modes (see “Modes of Operation” on page 95).
Table 14-8.

Waveform Generation Mode Bit Description
Timer/Counter
Mode of
Operation

TOP

Update of
OCRx at

TOV FlagSet on(1)(2)

Mode

WGM2

WGM1

WGM0

0

0

0

0

Normal0xFF

Immediate

MAX

1

0

0

1

PWM, Phase
Correct

0xFF

TOP

BOTTOM

2

0

1

0

CTC

OCRA

Immediate

MAX

3

0

1

1

Fast PWM

0xFF

TOP

MAX

4

1

0

0

Reserved

–

–

–

5

1

0

1

PWM, Phase
Correct

OCRA

TOP

BOTTOM

6

1

1

0

Reserved

–

–

–

7

1

1

1

Fast PWM

OCRA

TOP

TOP

Notes:

1. MAX= 0xFF

2. BOTTOM = 0x00

14.8.2Timer/Counter Control Register B – TCCR0B
Bit

7

6

5

4

3

2

1

0

FOC0A

FOC0B

–

–

WGM02

CS02

CS01

CS00

Read/Write

W

W

R

R

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TCCR0B• Bit 7 – FOC0A: Force Output Compare A
The FOC0A bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0A bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0A output ischanged according to its COM0A1:0 bits setting. Note that the FOC0A bit is implemented as a
strobe. Therefore it is the value present in the COM0A1:0 bits that determines the effect of theforced compare.

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A FOC0A strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0A as TOP.
The FOC0A bit is always read as zero.
• Bit 6 – FOC0B: Force Output Compare B
The FOC0B bit is only active when the WGM bits specify a non-PWM mode.
However, for ensuring compatibility with future devices, this bit must be set to zero when
TCCR0B is written when operating in PWM mode. When writing a logical one to the FOC0B bit,
an immediate Compare Match is forced on the Waveform Generation unit. The OC0B output ischanged according to its COM0B1:0 bits setting. Note that the FOC0B bit is implemented as a
strobe. Therefore it is the value present in the COM0B1:0 bits that determines the effect of theforced compare.
A FOC0B strobe will not generate any interrupt, nor will it clear the timer in CTC mode using
OCR0B as TOP.
The FOC0B bit is always read as zero.
• Bits 5:4 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
• Bit 3 – WGM02: Waveform Generation ModeSee the description in the “Timer/Counter Control Register A – TCCR0A” on page 100.
• Bits 2:0 – CS02:0: Clock SelectThe three Clock Select bits select the clock source to be used by the Timer/Counter.
Table 14-9.

Clock Select Bit Description

CS02

CS01

CS00

Description

0

0

0

No clock source (Timer/Counter stopped)

0

0

1

clkI/O/(No prescaling)

0

1

0

clkI/O/8 (From prescaler)

0

1

1

clkI/O/64 (From prescaler)

1

0

0

clkI/O/256 (From prescaler)

1

0

1

clkI/O/1024 (From prescaler)

1

1

0

External clock source on T0 pin. Clock on falling edge.

1

1

1

External clock source on T0 pin. Clock on rising edge.

If external pin modes are used for the Timer/Counter0, transitions on the T0 pin will clock thecounter even if the pin is configured as an output. This feature allows software control of thecounting.
14.8.3Timer/Counter Register – TCNT0
Bit

7

6

5

4

3

2

1

0

TCNT0[7:0]

104

TCNT0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

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AT90USB82/162
The Timer/Counter Register gives direct access, both for read and write operations, to theTimer/Counter unit 8-bit counter. Writing to the TCNT0 Register blocks (removes) the Compare
Match on the following timer clock. Modifying the counter (TCNT0) while the counter is running,
introduces a risk of missing a Compare Match between TCNT0 and the OCR0x Registers.
14.8.4

Output Compare Register A – OCR0A
Bit

7

6

5

4

3

2

1

0

OCR0A[7:0]

OCR0A

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

The Output Compare Register A contains an 8-bit value that is continuously compared with thecounter value (TCNT0). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC0A pin.
14.8.5

Output Compare Register B – OCR0B
Bit

7

6

5

4

3

2

1

0

OCR0B[7:0]

OCR0B

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

The Output Compare Register B contains an 8-bit value that is continuously compared with thecounter value (TCNT0). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OC0B pin.
14.8.6

Timer/Counter Interrupt Mask Register – TIMSK0
Bit

7

6

5

4

3

2

1

0

–

–

–

–

–

OCIE0B

OCIE0A

TOIE0

Read/Write

R

R

R

R

R

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TIMSK0• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
• Bit 2 – OCIE0B: Timer/Counter Output Compare Match B Interrupt Enable
When the OCIE0B bit is written to one, and the I-bit in the Status Register is set, theTimer/Counter Compare Match B interrupt is enabled. The corresponding interrupt is executed if
a Compare Match in Timer/Counter occurs, i.e., when the OCF0B bit is set in the Timer/Counter
Interrupt Flag Register – TIFR0.
• Bit 1 – OCIE0A: Timer/Counter0 Output Compare Match A Interrupt Enable
When the OCIE0A bit is written to one, and the I-bit in the Status Register is set, theTimer/Counter0 Compare Match A interrupt is enabled. The corresponding interrupt is executed
if a Compare Match in Timer/Counter0 occurs, i.e., when the OCF0A bit is set in theTimer/Counter 0 Interrupt Flag Register – TIFR0.
• Bit 0 – TOIE0: Timer/Counter0 Overflow Interrupt Enable
When the TOIE0 bit is written to one, and the I-bit in the Status Register is set, theTimer/Counter0 Overflow interrupt is enabled. The corresponding interrupt is executed if an
overflow in Timer/Counter0 occurs, i.e., when the TOV0 bit is set in the Timer/Counter 0 Interrupt Flag Register – TIFR0.

1057707E–AVR–11/08

14.8.7

Timer/Counter 0 Interrupt Flag Register – TIFR0
Bit

7

6

5

4

3

2

1

0

–

–

–

–

–

OCF0B

OCF0A

TOV0

Read/Write

R

R

R

R

R

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TIFR0

• Bits 7..3 – Res: Reserved Bits
These bits are reserved bits in the AT90USB82/162 and will always read as zero.
• Bit 2 – OCF0B: Timer/Counter 0 Output Compare B Match Flag
The OCF0B bit is set when a Compare Match occurs between the Timer/Counter and the data in
OCR0B – Output Compare Register0 B. OCF0B is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0B is cleared by writing a logic one tothe flag. When the I-bit in SREG, OCIE0B (Timer/Counter Compare B Match Interrupt Enable),and OCF0B are set, the Timer/Counter Compare Match Interrupt is executed.
• Bit 1 – OCF0A: Timer/Counter 0 Output Compare A Match Flag
The OCF0A bit is set when a Compare Match occurs between the Timer/Counter0 and the data
in OCR0A – Output Compare Register0. OCF0A is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, OCF0A is cleared by writing a logic one tothe flag. When the I-bit in SREG, OCIE0A (Timer/Counter0 Compare Match Interrupt Enable),and OCF0A are set, the Timer/Counter0 Compare Match Interrupt is executed.
• Bit 0 – TOV0: Timer/Counter0 Overflow Flag
The bit TOV0 is set when an overflow occurs in Timer/Counter0. TOV0 is cleared by hardware
when executing the corresponding interrupt handling vector. Alternatively, TOV0 is cleared bywriting a logic one to the flag. When the SREG I-bit, TOIE0 (Timer/Counter0 Overflow Interrupt
Enable), and TOV0 are set, the Timer/Counter0 Overflow interrupt is executed.
The setting of this flag is dependent of the WGM02:0 bit setting. Refer to Table 14-8, “Waveform
Generation Mode Bit Description” on page 103.

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15. 16-bit Timer/Counter 1 with PWM
The 16-bit Timer/Counter 1 unit allows accurate program execution timing (event management),
wave generation, and signal timing measurement. The main features are:• True 16-bit Design (i.e., Allows 16-bit PWM)
• Three independent Output Compare Units• Double Buffered Output Compare Registers• One Input Capture Unit
• Input Capture Noise Canceler• Clear Timer on Compare Match (Auto Reload)• Glitch-free, Phase Correct Pulse Width Modulator (PWM)• Variable PWM Period• Frequency Generator• External Event Counter• Five independent interrupt sources (TOV1, OCF1A, OCF1B, OCF1C, ICF1)

15.1

Overview
Most register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number (for this product, only n=1 is available), and a lower case “x”
replaces the Output Compare unit channel. However, when using the register or bit defines in a
program, the precise form must be used, i.e., TCNT1 for accessing Timer/Counter1 countervalue and so on.
A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 15-1. For the actual
placement of I/O pins, see “Pinout AT90USB82/162” on page 3. CPU accessible I/O Registers,
including I/O bits and I/O pins, are shown in bold. The device-specific I/O Register and bit locations are listed in the “16-bit Timer/Counter 1 with PWM” on page 107.
The Power Reduction Timer/Counter1 bit, PRTIM1, in “Power Reduction Register 0 - PRR0” onpage 43 must be written to zero to enable Timer/Counter1 module.

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Figure 15-1. 16-bit Timer/Counter Block Diagram(1)
Count
Clear
Direction

TOVn(Int.Req.)
Control Logic

TCLK

Clock SelectEdge
Detector

TOP

Tn

BOTTOM( From Prescaler )Timer/Counter
TCNTn

=

=0
OCFnA
(Int.Req.)
Waveform
Generation

=

OCnA

OCRnA
OCFnB
(Int.Req.)

Fixed
TOP
ValuesWaveform
Generation

DATABUS

=

OCnB

OCRnB
OCFnC
(Int.Req.)
Waveform
Generation

=

OCnC

OCRnC
( From Analog
Comparator Ouput )ICFn (Int.Req.)
Edge
Detector

ICRn

Noise
Canceler
ICPn

TCCRnA

Note:

15.1.1

TCCRnB

TCCRnC

1. Refer to Figure 1-1 on page 3, Table 11-3 on page 74, and Table 11-6 on page 77 forTimer/Counter1 pin placement and description.

Registers
The Timer/Counter (TCNTn), Output Compare Registers (OCRnA/B/C), and Input Capture Register (ICRn) are all 16-bit registers. Special procedures must be followed when accessing the 16bit registers. These procedures are described in the section “Accessing 16-bit Registers” onpage 109. The Timer/Counter Control Registers (TCCRnA/B/C) are 8-bit registers and have no
CPU access restrictions. Interrupt requests (shorten as Int.Req.) signals are all visible in theTimer Interrupt Flag Register (TIFRn). All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSKn). TIFRn and TIMSKn are not shown in the figure since theseregisters are shared by other timer units.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the Tn pin. The Clock Select logic block controls which clock source and edge the Timer/Counteruses to increment (or decrement) its value. The Timer/Counter is inactive when no clock source
is selected. The output from the clock select logic is referred to as the timer clock (clkTn).
The double buffered Output Compare Registers (OCRnA/B/C) are compared with theTimer/Counter value at all time. The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency output on the Output Compare pin (OCnA/B/C).

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See “Output Compare Units” on page 116.. The compare match event will also set the Compare
Match Flag (OCFnA/B/C) which can be used to generate an Output Compare interrupt request.
The Input Capture Register can capture the Timer/Counter value at a given external (edge triggered) event on either the Input Capture pin (ICPn) or on the Analog Comparator pins (See“Analog Comparator” on page 223.) The Input Capture unit includes a digital filtering unit (Noise
Canceler) for reducing the chance of capturing noise spikes.
The TOP value, or maximum Timer/Counter value, can in some modes of operation be definedby either the OCRnA Register, the ICRn Register, or by a set of fixed values. When using
OCRnA as TOP value in a PWM mode, the OCRnA Register can not be used for generating a
PWM output. However, the TOP value will in this case be double buffered allowing the TOP
value to be changed in run time. If a fixed TOP value is required, the ICRn Register can be used
as an alternative, freeing the OCRnA to be used as PWM output.
15.1.2

Definitions
The following definitions are used extensively throughout the document:

15.2

BOTTOM

The counter reaches the BOTTOM when it becomes 0x0000.

MAX

The counter reaches its MAXimum when it becomes 0xFFFF (decimal 65535).

TOP

The counter reaches the TOP when it becomes equal to the highest value in the countsequence. The TOP value can be assigned to be one of the fixed values: 0x00FF,
0x01FF, or 0x03FF, or to the value stored in the OCRnA or ICRn Register. The
assignment is dependent of the mode of operation.

Accessing 16-bit Registers
The TCNTn, OCRnA/B/C, and ICRn are 16-bit registers that can be accessed by the AVR CPU
via the 8-bit data bus. The 16-bit register must be byte accessed using two read or write operations. Each 16-bit timer has a single 8-bit register for temporary storing of the high byte of the 16bit access. The same Temporary Register is shared between all 16-bit registers within each 16bit timer. Accessing the low byte triggers the 16-bit read or write operation. When the low byte ofa 16-bit register is written by the CPU, the high byte stored in the Temporary Register, and the
low byte written are both copied into the 16-bit register in the same clock cycle. When the low
byte of a 16-bit register is read by the CPU, the high byte of the 16-bit register is copied into the
Temporary Register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the Temporary Register for the high byte. Reading the OCRnA/B/C
16-bit registers does not involve using the Temporary Register.
To do a 16-bit write, the high byte must be written before the low byte. For a 16-bit read, the low
byte must be read before the high byte.
The following code examples show how to access the 16-bit timer registers assuming that nointerrupts updates the temporary register. The same principle can be used directly for accessing
the OCRnA/B/C and ICRn Registers. Note that when using “C”, the compiler handles the 16-bit
access.

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Assembly Code Examples(1)...
; Set TCNTn to 0x01FF
ldi r17,0x01
ldi r16,0xFF
out TCNTnH,r17
out TCNTnL,r16; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH...

C Code Examples(1)unsigned int i;...
/* Set TCNTn to 0x01FF */TCNTn = 0x1FF;/* Read TCNTn into i */i = TCNTn;
...
Note:

1. See “About Code Examples” on page 7.

The assembly code example returns the TCNTn value in the r17:r16 register pair.
It is important to notice that accessing 16-bit registers are atomic operations. If an interrupt
occurs between the two instructions accessing the 16-bit register, and the interrupt code
updates the temporary register by accessing the same or any other of the 16-bit Timer Registers, then the result of the access outside the interrupt will be corrupted. Therefore, when boththe main code and the interrupt code update the temporary register, the main code must disable
the interrupts during the 16-bit access.
The following code examples show how to do an atomic read of the TCNTn Register contents.
Reading any of the OCRnA/B/C or ICRn Registers can be done by using the same principle.

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Assembly Code Example(1)TIM16_ReadTCNTn:; Save global interrupt flagin r18,SREG; Disable interrupts
cli; Read TCNTn into r17:r16
in r16,TCNTnL
in r17,TCNTnH; Restore global interrupt flagout SREG,r18
ret

C Code Example(1)unsigned int TIM16_ReadTCNTn( void ){unsigned char sreg;
unsigned int i;/* Save global interrupt flag */sreg = SREG;/* Disable interrupts */__disable_interrupt();/* Read TCNTn into i */i = TCNTn;/* Restore global interrupt flag */SREG = sreg;
return i;}
Note:

1. See “About Code Examples” on page 7.

The assembly code example returns the TCNTn value in the r17:r16 register pair.

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The following code examples show how to do an atomic write of the TCNTn Register contents.
Writing any of the OCRnA/B/C or ICRn Registers can be done by using the same principle.
Assembly Code Example(1)TIM16_WriteTCNTn:; Save global interrupt flagin r18,SREG; Disable interrupts
cli; Set TCNTn to r17:r16
out TCNTnH,r17
out TCNTnL,r16; Restore global interrupt flagout SREG,r18
ret

C Code Example(1)void TIM16_WriteTCNTn( unsigned int i ){unsigned char sreg;
unsigned int i;/* Save global interrupt flag */sreg = SREG;/* Disable interrupts */__disable_interrupt();/* Set TCNTn to i */TCNTn = i;/* Restore global interrupt flag */SREG = sreg;}
Note:

1. See “About Code Examples” on page 7.

The assembly code example requires that the r17:r16 register pair contains the value to be written to TCNTn.
15.2.1

15.3

Reusing the Temporary High Byte Register
If writing to more than one 16-bit register where the high byte is the same for all registers written,
then the high byte only needs to be written once. However, note that the same rule of atomic
operation described previously also applies in this case.

Timer/Counter Clock Sources
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CSn2:0) bits
located in the Timer/Counter control Register B (TCCRnB). For details on clock sources andprescaler, see “Timer/Counter0 and Timer/Counter1 Prescalers” on page 88.

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15.4

Counter Unit
The main part of the 16-bit Timer/Counter is the programmable 16-bit bi-directional counter unit.
Figure 15-2 shows a block diagram of the counter and its surroundings.
Figure 15-2. Counter Unit Block Diagram
DATA BUS (8-bit)
TOVn(Int.Req.)
TEMP (8-bit)
Clock SelectCount
TCNTnH (8-bit)

TCNTnL (8-bit)

Clear
Direction

TCNTn (16-bit Counter)

Control Logic

clkTn

Edge
Detector

Tn( From Prescaler )TOP

BOTTOM

Signal description (internal signals):Count

Increment or decrement TCNTn by 1.

Direction

Select between increment and decrement.

Clear

Clear TCNTn (set all bits to zero).

clkTnTimer/Counter clock.

TOP

Signalize that TCNTn has reached maximum value.

BOTTOM

Signalize that TCNTn has reached minimum value (zero).

The 16-bit counter is mapped into two 8-bit I/O memory locations: Counter High (TCNTnH) containing the upper eight bits of the counter, and Counter Low (TCNTnL) containing the lower eightbits. The TCNTnH Register can only be indirectly accessed by the CPU. When the CPU does anaccess to the TCNTnH I/O location, the CPU accesses the high byte temporary register (TEMP).
The temporary register is updated with the TCNTnH value when the TCNTnL is read, and
TCNTnH is updated with the temporary register value when TCNTnL is written. This allows the
CPU to read or write the entire 16-bit counter value within one clock cycle via the 8-bit data bus.
It is important to notice that there are special cases of writing to the TCNTn Register when the
counter is counting that will give unpredictable results. The special cases are described in thesections where they are of importance.
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clkTn). The clkTn can be generated from an external or internal clock source,
selected by the Clock Select bits (CSn2:0). When no clock source is selected (CSn2:0 = 0) the
timer is stopped. However, the TCNTn value can be accessed by the CPU, independent of
whether clkTn is present or not. A CPU write overrides (has priority over) all counter clear orcount operations.
The counting sequence is determined by the setting of the Waveform Generation mode bits
(WGMn3:0) located in the Timer/Counter Control Registers A and B (TCCRnA and TCCRnB).
There are close connections between how the counter behaves (counts) and how waveforms
are generated on the Output Compare outputs OCnx. For more details about advanced counting
sequences and waveform generation, see “Modes of Operation” on page 119.

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The Timer/Counter Overflow Flag (TOVn) is set according to the mode of operation selected by
the WGMn3:0 bits. TOVn can be used for generating a CPU interrupt.

15.5

Input Capture Unit
The Timer/Counter incorporates an input capture unit that can capture external events and givethem a time-stamp indicating time of occurrence. The external signal indicating an event, or multiple events, can be applied via the ICPn pin or alternatively, for the Timer/Counter1 only, via theAnalog Comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle,
and other features of the signal applied. Alternatively the time-stamps can be used for creating alog of the events.
The Input Capture unit is illustrated by the block diagram shown in Figure 15-3. The elements ofthe block diagram that are not directly a part of the input capture unit are gray shaded. The small“n” in register and bit names indicates the Timer/Counter number.
Figure 15-3. Input Capture Unit Block Diagram

DATA BUS (8-bit)

TEMP (8-bit)

ICRnH (8-bit)
WRITE

ICRnL (8-bit)

TCNTnH (8-bit)

ICRn (16-bit Register)ACO*
AnalogComparator

ACIC*

TCNTnL (8-bit)

TCNTn (16-bit Counter)

ICNC

ICES

Noise
CancelerEdge
Detector

ICFn (Int.Req.)

ICPn

Note:

The Analog Comparator Output (ACO) can only trigger the Timer/Counter1 ICP – notTimer/Counter3, 4 or 5.

When a change of the logic level (an event) occurs on the Input Capture Pin (ICPn), alternatively
on the analog Comparator output (ACO), and this change confirms to the setting of the edge
detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter(TCNTn) is written to the Input Capture Register (ICRn). The Input Capture Flag (ICFn) is set atthe same system clock as the TCNTn value is copied into ICRn Register. If enabled (TICIEn =1), the input capture flag generates an input capture interrupt. The ICFn flag is automatically
cleared when the interrupt is executed. Alternatively the ICFn flag can be cleared by software by
writing a logical one to its I/O bit location.

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Reading the 16-bit value in the Input Capture Register (ICRn) is done by first reading the low
byte (ICRnL) and then the high byte (ICRnH). When the low byte is read the high byte is copied
into the high byte Temporary Register (TEMP). When the CPU reads the ICRnH I/O location it
will access the TEMP Register.
The ICRn Register can only be written when using a Waveform Generation mode that utilizes
the ICRn Register for defining the counter’s TOP value. In these cases the Waveform Generation mode (WGMn3:0) bits must be set before the TOP value can be written to the ICRn
Register. When writing the ICRn Register the high byte must be written to the ICRnH I/O location
before the low byte is written to ICRnL.
For more information on how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 109.
15.5.1

Input Capture Trigger Source
The main trigger source for the input capture unit is the Input Capture Pin (ICPn).
Timer/Counter1 can alternatively use the analog comparator output as trigger source for the
input capture unit. The Analog Comparator is selected as trigger source by setting the analog
Comparator Input Capture (ACIC) bit in the Analog Comparator Control and Status Register(ACSR). Be aware that changing trigger source can trigger a capture. The input capture flag
must therefore be cleared after the change.
Both the Input Capture Pin (ICPn) and the Analog Comparator output (ACO) inputs are sampledusing the same technique as for the Tn pin (Figure 13-1 on page 88). The edge detector is also
identical. However, when the noise canceler is enabled, additional logic is inserted before theedge detector, which increases the delay by four system clock cycles. Note that the input of thenoise canceler and edge detector is always enabled unless the Timer/Counter is set in a Waveform Generation mode that uses ICRn to define TOP.
An input capture can be triggered by software by controlling the port of the ICPn pin.

15.5.2

Noise Canceler
The noise canceler improves noise immunity by using a simple digital filtering scheme. The
noise canceler input is monitored over four samples, and all four must be equal for changing theoutput that in turn is used by the edge detector.
The noise canceler is enabled by setting the Input Capture Noise Canceler (ICNCn) bit inTimer/Counter Control Register B (TCCRnB). When enabled the noise canceler introduces additional four system clock cycles of delay from a change applied to the input, to the update of the
ICRn Register. The noise canceler uses the system clock and is therefore not affected by theprescaler.

15.5.3Using the Input Capture Unit
The main challenge when using the Input Capture unit is to assign enough processor capacity
for handling the incoming events. The time between two events is critical. If the processor has
not read the captured value in the ICRn Register before the next event occurs, the ICRn will beoverwritten with a new value. In this case the result of the capture will be incorrect.
When using the Input Capture interrupt, the ICRn Register should be read as early in the interrupt handler routine as possible. Even though the Input Capture interrupt has relatively highpriority, the maximum interrupt response time is dependent on the maximum number of clock
cycles it takes to handle any of the other interrupt requests.

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Using the Input Capture unit in any mode of operation when the TOP value (resolution) is
actively changed during operation, is not recommended.
Measurement of an external signal’s duty cycle requires that the trigger edge is changed after
each capture. Changing the edge sensing must be done as early as possible after the ICRn
Register has been read. After a change of the edge, the Input Capture Flag (ICFn) must be
cleared by software (writing a logical one to the I/O bit location). For measuring frequency only,
the clearing of the ICFn Flag is not required (if an interrupt handler is used).

15.6

Output Compare Units
The 16-bit comparator continuously compares TCNTn with the Output Compare Register(OCRnx). If TCNT equals OCRnx the comparator signals a match. A match will set the Output
Compare Flag (OCFnx) at the next timer clock cycle. If enabled (OCIEnx = 1), the Output Compare Flag generates an Output Compare interrupt. The OCFnx Flag is automatically cleared
when the interrupt is executed. Alternatively the OCFnx Flag can be cleared by software by writing a logical one to its I/O bit location. The Waveform Generator uses the match signal togenerate an output according to operating mode set by the Waveform Generation mode
(WGMn3:0) bits and Compare Output mode (COMnx1:0) bits. The TOP and BOTTOM signals
are used by the Waveform Generator for handling the special cases of the extreme values insome modes of operation (See “Modes of Operation” on page 119.)A special feature of Output Compare unit A allows it to define the Timer/Counter TOP value (i.e.,counter resolution). In addition to the counter resolution, the TOP value defines the period time
for waveforms generated by the Waveform Generator.
Figure 15-4 shows a block diagram of the Output Compare unit. The small “n” in the register andbit names indicates the device number (n = n for Timer/Counter n), and the “x” indicates Output
Compare unit (A/B/C). The elements of the block diagram that are not directly a part of the Output Compare unit are gray shaded.
Figure 15-4. Output Compare Unit, Block Diagram
DATA BUS (8-bit)

TEMP (8-bit)

OCRnxH Buf. (8-bit)

OCRnxL Buf. (8-bit)

TCNTnH (8-bit)

OCRnx Buffer (16-bit Register)

OCRnxH (8-bit)

TCNTnL (8-bit)

TCNTn (16-bit Counter)

OCRnxL (8-bit)

OCRnx (16-bit Register)= (16-bit Comparator )OCFnx (Int.Req.)TOP
BOTTOM

Waveform Generator

WGMn3:0116

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OCnx

COMnx1:0

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The OCRnx Register is double buffered when using any of the twelve Pulse Width Modulation(PWM) modes. For the Normal and Clear Timer on Compare (CTC) modes of operation, thedouble buffering is disabled. The double buffering synchronizes the update of the OCRnx Compare Register to either TOP or BOTTOM of the counting sequence. The synchronization
prevents the occurrence of odd-length, non-symmetrical PWM pulses, thereby making the output glitch-free.
The OCRnx Register access may seem complex, but this is not case. When the double buffering
is enabled, the CPU has access to the OCRnx Buffer Register, and if double buffering is disabled the CPU will access the OCRnx directly. The content of the OCR1x (Buffer or Compare)
Register is only changed by a write operation (the Timer/Counter does not update this register
automatically as the TCNT1 and ICR1 Register). Therefore OCR1x is not read via the high byte
temporary register (TEMP). However, it is a good practice to read the low byte first as whenaccessing other 16-bit registers. Writing the OCRnx Registers must be done via the TEMP Register since the compare of all 16 bits is done continuously. The high byte (OCRnxH) has to be
written first. When the high byte I/O location is written by the CPU, the TEMP Register will be
updated by the value written. Then when the low byte (OCRnxL) is written to the lower eight bits,
the high byte will be copied into the upper 8-bits of either the OCRnx buffer or OCRnx Compare
Register in the same system clock cycle.
For more information of how to access the 16-bit registers refer to “Accessing 16-bit Registers”
on page 109.
15.6.1Force Output Compare
In non-PWM Waveform Generation modes, the match output of the comparator can be forced bywriting a one to the Force Output Compare (FOCnx) bit. Forcing compare match will not set the
OCFnx Flag or reload/clear the timer, but the OCnx pin will be updated as if a real compare
match had occurred (the COMn1:0 bits settings define whether the OCnx pin is set, cleared or
toggled).

15.6.2Compare Match Blocking by TCNTn Write
All CPU writes to the TCNTn Register will block any compare match that occurs in the next timer
clock cycle, even when the timer is stopped. This feature allows OCRnx to be initialized to thesame value as TCNTn without triggering an interrupt when the Timer/Counter clock is enabled.

15.6.3Using the Output Compare Unit
Since writing TCNTn in any mode of operation will block all compare matches for one timer clock
cycle, there are risks involved when changing TCNTn when using any of the Output Compare
channels, independent of whether the Timer/Counter is running or not. If the value written to
TCNTn equals the OCRnx value, the compare match will be missed, resulting in incorrect waveform generation. Do not write the TCNTn equal to TOP in PWM modes with variable TOP
values. The compare match for the TOP will be ignored and the counter will continue to 0xFFFF.
Similarly, do not write the TCNTn value equal to BOTTOM when the counter is downcounting.
The setup of the OCnx should be performed before setting the Data Direction Register for the
port pin to output. The easiest way of setting the OCnx value is to use the Force Output Compare (FOCnx) strobe bits in Normal mode. The OCnx Register keeps its value even whenchanging between Waveform Generation modes.
Be aware that the COMnx1:0 bits are not double buffered together with the compare value.
Changing the COMnx1:0 bits will take effect immediately.

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15.7

Compare Match Output Unit
The Compare Output mode (COMnx1:0) bits have two functions. The Waveform Generator uses
the COMnx1:0 bits for defining the Output Compare (OCnx) state at the next compare match.
Secondly the COMnx1:0 bits control the OCnx pin output source. Figure 15-5 shows a simplified
schematic of the logic affected by the COMnx1:0 bit setting. The I/O Registers, I/O bits, and I/Opins in the figure are shown in bold. Only the parts of the general I/O Port Control Registers(DDR and PORT) that are affected by the COMnx1:0 bits are shown. When referring to theOCnx state, the reference is for the internal OCnx Register, not the OCnx pin. If a system reset
occur, the OCnx Register is reset to “0”.
Figure 15-5. Compare Match Output Unit, Schematic

COMnx1
COMnx0
FOCnx

Waveform
Generator

D

Q
1

OCnx

DATA BUS

D

0

OCnx
Pin

Q

PORT
D

Q

DDR
clk I/O

The general I/O port function is overridden by the Output Compare (OCnx) from the Waveform
Generator if either of the COMnx1:0 bits are set. However, the OCnx pin direction (input or output) is still controlled by the Data Direction Register (DDR) for the port pin. The Data Direction
Register bit for the OCnx pin (DDR_OCnx) must be set as output before the OCnx value is visible on the pin. The port override function is generally independent of the Waveform Generationmode, but there are some exceptions. Refer to Table 15-1, Table 15-2 and Table 15-3 fordetails.
The design of the Output Compare pin logic allows initialization of the OCnx state before the output is enabled. Note that some COMnx1:0 bit settings are reserved for certain modes ofoperation. See “16-bit Timer/Counter 1 with PWM” on page 107.
The COMnx1:0 bits have no effect on the Input Capture unit.
15.7.1

118

Compare Output Mode and Waveform Generation
The Waveform Generator uses the COMnx1:0 bits differently in normal, CTC, and PWM modes.
For all modes, setting the COMnx1:0 = 0 tells the Waveform Generator that no action on the
OCnx Register is to be performed on the next compare match. For compare output actions in the

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non-PWM modes refer to Table 15-1 on page 129. For fast PWM mode refer to Table 15-2 onpage 129, and for phase correct and phase and frequency correct PWM refer to Table 15-3 onpage 130.
A change of the COMnx1:0 bits state will have effect at the first compare match after the bits are
written. For non-PWM modes, the action can be forced to have immediate effect by using the
FOCnx strobe bits.

15.8

Modes of Operation
The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, isdefined by the combination of the Waveform Generation mode (WGMn3:0) and Compare Output
mode (COMnx1:0) bits. The Compare Output mode bits do not affect the counting sequence,
while the Waveform Generation mode bits do. The COMnx1:0 bits control whether the PWM output generated should be inverted or not (inverted or non-inverted PWM). For non-PWM modes
the COMnx1:0 bits control whether the output should be set, cleared or toggle at a compare
match (See “Compare Match Output Unit” on page 118.)For detailed timing information refer to “Timer/Counter Timing Diagrams” on page 126.

15.8.1

Normal Mode
The simplest mode of operation is the Normal mode (WGMn3:0 = 0). In this mode the counting
direction is always up (incrementing), and no counter clear is performed. The counter simply
overruns when it passes its maximum 16-bit value (MAX = 0xFFFF) and then restarts from the
BOTTOM (0x0000). In normal operation the Timer/Counter Overflow Flag (TOVn) will be set in
the same timer clock cycle as the TCNTn becomes zero. The TOVn Flag in this case behaves
like a 17th bit, except that it is only set, not cleared. However, combined with the timer overflow
interrupt that automatically clears the TOVn Flag, the timer resolution can be increased by software. There are no special cases to consider in the Normal mode, a new counter value can be
written anytime.
The Input Capture unit is easy to use in Normal mode. However, observe that the maximum
interval between the external events must not exceed the resolution of the counter. If the interval
between events are too long, the timer overflow interrupt or the prescaler must be used toextend the resolution for the capture unit.
The Output Compare units can be used to generate interrupts at some given time. Using the
Output Compare to generate waveforms in Normal mode is not recommended, since this will
occupy too much of the CPU time.

15.8.2

Clear Timer on Compare Match (CTC) ModeIn Clear Timer on Compare or CTC mode (WGMn3:0 = 4 or 12), the OCRnA or ICRn Registerare used to manipulate the counter resolution. In CTC mode the counter is cleared to zero when
the counter value (TCNTn) matches either the OCRnA (WGMn3:0 = 4) or the ICRn (WGMn3:0 =12). The OCRnA or ICRn define the top value for the counter, hence also its resolution. Thismode allows greater control of the compare match output frequency. It also simplifies the operation of counting external events.
The timing diagram for the CTC mode is shown in Figure 15-6. The counter value (TCNTn)
increases until a compare match occurs with either OCRnA or ICRn, and then counter (TCNTn)
is cleared.

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Figure 15-6. CTC Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set(Interrupt on TOP)

TCNTn

OCnA
(Toggle)Period(COMnA1:0 = 1)

1

2

3

4

An interrupt can be generated at each time the counter value reaches the TOP value by either
using the OCFnA or ICFn Flag according to the register used to define the TOP value. If theinterrupt is enabled, the interrupt handler routine can be used for updating the TOP value. However, changing the TOP to a value close to BOTTOM when the counter is running with none or alow prescaler value must be done with care since the CTC mode does not have the double buffering feature. If the new value written to OCRnA or ICRn is lower than the current value of
TCNTn, the counter will miss the compare match. The counter will then have to count to its maximum value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
In many cases this feature is not desirable. An alternative will then be to use the fast PWM modeusing OCRnA for defining TOP (WGMn3:0 = 15) since the OCRnA then will be double buffered.
For generating a waveform output in CTC mode, the OCnA output can be set to toggle its logicallevel on each compare match by setting the Compare Output mode bits to toggle mode
(COMnA1:0 = 1). The OCnA value will not be visible on the port pin unless the data direction forthe pin is set to output (DDR_OCnA = 1). The waveform generated will have a maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). The waveform frequency isdefined by the following equation:
f clk_I/O
f OCnA = --------------------------------------------------2 ⋅ N ⋅ ( 1 + OCRnA )The N variable represents the prescaler factor (1, 8, 64, 256, or 1024).
As for the Normal mode of operation, the TOVn Flag is set in the same timer clock cycle that thecounter counts from MAX to 0x0000.
15.8.3120

Fast PWM Mode
The fast Pulse Width Modulation or fast PWM mode (WGMn3:0 = 5, 6, 7, 14, or 15) provides ahigh frequency PWM waveform generation option. The fast PWM differs from the other PWM
options by its single-slope operation. The counter counts from BOTTOM to TOP then restarts
from BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is set on
the compare match between TCNTn and OCRnx, and cleared at TOP. In inverting Compare
Output mode output is cleared on compare match and set at TOP. Due to the single-slope operation, the operating frequency of the fast PWM mode can be twice as high as the phase correct
and phase and frequency correct PWM modes that use dual-slope operation. This high frequency makes the fast PWM mode well suited for power regulation, rectification, and DAC
applications. High frequency allows physically small sized external components (coils, capacitors), hence reduces total system cost.

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The PWM resolution for fast PWM can be fixed to 8-, 9-, or 10-bit, or defined by either ICRn or
OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can becalculated by using the following equation:log ( TOP + 1 )R FPWM = ----------------------------------log ( 2 )In fast PWM mode the counter is incremented until the counter value matches either one of the
fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 5, 6, or 7), the value in ICRn (WGMn3:0 =14), or the value in OCRnA (WGMn3:0 = 15). The counter is then cleared at the following timer
clock cycle. The timing diagram for the fast PWM mode is shown in Figure 15-7. The figure
shows fast PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in thetiming diagram shown as a histogram for illustrating the single-slope operation. The diagram
includes non-inverted and inverted PWM outputs. The small horizontal line marks on the TCNTnslopes represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will
be set when a compare match occurs.
Figure 15-7. Fast PWM Mode, Timing Diagram
OCRnx / TOP Update
and TOVn Interrupt Flag
Set and OCnA Interrupt
Flag Set or ICFn
Interrupt Flag Set(Interrupt on TOP)

TCNTn

OCnx

(COMnx1:0 = 2)

OCnx

(COMnx1:0 = 3)

Period

1

2

3

4

5

6

7

8

The Timer/Counter Overflow Flag (TOVn) is set each time the counter reaches TOP. In addition
the OCnA or ICFn Flag is set at the same timer clock cycle as TOVn is set when either OCRnAor ICRn is used for defining the TOP value. If one of the interrupts are enabled, the interrupt handler routine can be used for updating the TOP and compare values.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of theCompare Registers, a compare match will never occur between the TCNTn and the OCRnx.
Note that when using fixed TOP values the unused bits are masked to zero when any of the
OCRnx Registers are written.
The procedure for updating ICRn differs from updating OCRnA when used for defining the TOP
value. The ICRn Register is not double buffered. This means that if ICRn is changed to a low
value when the counter is running with none or a low prescaler value, there is a risk that the new
ICRn value written is lower than the current value of TCNTn. The result will then be that thecounter will miss the compare match at the TOP value. The counter will then have to count to the
MAX value (0xFFFF) and wrap around starting at 0x0000 before the compare match can occur.
The OCRnA Register however, is double buffered. This feature allows the OCRnA I/O location
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to be written anytime. When the OCRnA I/O location is written the value written will be put into
the OCRnA Buffer Register. The OCRnA Compare Register will then be updated with the value
in the Buffer Register at the next timer clock cycle the TCNTn matches TOP. The update is doneat the same timer clock cycle as the TCNTn is cleared and the TOVn Flag is set.
Using the ICRn Register for defining TOP works well when using fixed TOP values. By using
ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,if the base PWM frequency is actively changed (by changing the TOP value), using the OCRnA
as TOP is clearly a better choice due to its double buffer feature.
In fast PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins.
Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted PWM output
can be generated by setting the COMnx1:0 to three (see Table on page 129). The actual OCnx
value will only be visible on the port pin if the data direction for the port pin is set as output(DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx Register at
the compare match between OCRnx and TCNTn, and clearing (or setting) the OCnx Register at
the timer clock cycle the counter is cleared (changes from TOP to BOTTOM).
The PWM frequency for the output can be calculated by the following equation:
f clk_I/O
f OCnxPWM = ----------------------------------N ⋅ ( 1 + TOP )The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx Register represents special cases when generating a PWM
waveform output in the fast PWM mode. If the OCRnx is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock cycle. Setting the OCRnx equal to TOP
will result in a constant high or low output (depending on the polarity of the output set by the
COMnx1:0 bits.)
A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by setting OCnA to toggle its logical level on each compare match (COMnA1:0 = 1). This applies only
if OCR1A is used to define the TOP value (WGM13:0 = 15). The waveform generated will havea maximum frequency of fOCnA = fclk_I/O/2 when OCRnA is set to zero (0x0000). This feature issimilar to the OCnA toggle in CTC mode, except the double buffer feature of the Output Compare unit is enabled in the fast PWM mode.
15.8.4Phase Correct PWM Mode
The phase correct Pulse Width Modulation or phase correct PWM mode (WGMn3:0 = 1, 2, 3,
10, or 11) provides a high resolution phase correct PWM waveform generation option. The
phase correct PWM mode is, like the phase and frequency correct PWM mode, based on a dualslope operation. The counter counts repeatedly from BOTTOM (0x0000) to TOP and then from
TOP to BOTTOM. In non-inverting Compare Output mode, the Output Compare (OCnx) is
cleared on the compare match between TCNTn and OCRnx while upcounting, and set on thecompare match while downcounting. In inverting Output Compare mode, the operation isinverted. The dual-slope operation has lower maximum operation frequency than single slope
operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes
are preferred for motor control applications.
The PWM resolution for the phase correct PWM mode can be fixed to 8-, 9-, or 10-bit, or definedby either ICRn or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to122

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0x0003), and the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits can be calculated by using the following equation:log ( TOP + 1 )R PCPWM = ----------------------------------log ( 2 )In phase correct PWM mode the counter is incremented until the counter value matches either
one of the fixed values 0x00FF, 0x01FF, or 0x03FF (WGMn3:0 = 1, 2, or 3), the value in ICRn
(WGMn3:0 = 10), or the value in OCRnA (WGMn3:0 = 11). The counter has then reached the
TOP and changes the count direction. The TCNTn value will be equal to TOP for one timer clock
cycle. The timing diagram for the phase correct PWM mode is shown on Figure 15-8. The figure
shows phase correct PWM mode when OCRnA or ICRn is used to define TOP. The TCNTnvalue is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The
diagram includes non-inverted and inverted PWM outputs. The small horizontal line marks on
the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will be set when a compare match occurs.
Figure 15-8. Phase Correct PWM Mode, Timing Diagram
OCRnx/TOP Update and
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set(Interrupt on TOP)TOVn Interrupt Flag Set(Interrupt on Bottom)

TCNTn

OCnx

(COMnx1:0 = 2)

OCnx

(COMnx1:0 = 3)

Period1

2

3

4

The Timer/Counter Overflow Flag (TOVn) is set each time the counter reaches BOTTOM. Wheneither OCRnA or ICRn is used for defining the TOP value, the OCnA or ICFn Flag is set accordingly at the same timer clock cycle as the OCRnx Registers are updated with the double buffer
value (at TOP). The Interrupt Flags can be used to generate an interrupt each time the counterreaches the TOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of theCompare Registers, a compare match will never occur between the TCNTn and the OCRnx.
Note that when using fixed TOP values, the unused bits are masked to zero when any of the
OCRnx Registers are written. As the third period shown in Figure 15-8 illustrates, changing the
TOP actively while the Timer/Counter is running in the phase correct mode can result in an
unsymmetrical output. The reason for this can be found in the time of update of the OCRnx Reg123
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ister. Since the OCRnx update occurs at TOP, the PWM period starts and ends at TOP. Thisimplies that the length of the falling slope is determined by the previous TOP value, while thelength of the rising slope is determined by the new TOP value. When these two values differ thetwo slopes of the period will differ in length. The difference in length gives the unsymmetricalresult on the output.
It is recommended to use the phase and frequency correct mode instead of the phase correctmode when changing the TOP value while the Timer/Counter is running. When using a static
TOP value there are practically no differences between the two modes of operation.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the
OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted
PWM output can be generated by setting the COMnx1:0 to three (See Table 15-3 on page 130).
The actual OCnx value will only be visible on the port pin if the data direction for the port pin isset as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx
Register at the compare match between OCRnx and TCNTn when the counter increments, andclearing (or setting) the OCnx Register at compare match between OCRnx and TCNTn when
the counter decrements. The PWM frequency for the output when using phase correct PWM canbe calculated by the following equation:
f clk_I/O
f OCnxPCPWM = ---------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx Register represent special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM theoutput will be continuously low and if set equal to TOP the output will be continuously high for
non-inverted PWM mode. For inverted PWM the output will have the opposite logic values. If
OCR1A is used to define the TOP value (WGM13:0 = 11) and COM1A1:0 = 1, the OC1A output
will toggle with a 50% duty cycle.
15.8.5Phase and Frequency Correct PWM Mode
The phase and frequency correct Pulse Width Modulation, or phase and frequency correct PWM
mode (WGMn3:0 = 8 or 9) provides a high resolution phase and frequency correct PWM waveform generation option. The phase and frequency correct PWM mode is, like the phase correct
PWM mode, based on a dual-slope operation. The counter counts repeatedly from BOTTOM(0x0000) to TOP and then from TOP to BOTTOM. In non-inverting Compare Output mode, theOutput Compare (OCnx) is cleared on the compare match between TCNTn and OCRnx while
upcounting, and set on the compare match while downcounting. In inverting Compare Output
mode, the operation is inverted. The dual-slope operation gives a lower maximum operation frequency compared to the single-slope operation. However, due to the symmetric feature of thedual-slope PWM modes, these modes are preferred for motor control applications.
The main difference between the phase correct, and the phase and frequency correct PWM
mode is the time the OCRnx Register is updated by the OCRnx Buffer Register, (see Figure 158 and Figure 15-9).
The PWM resolution for the phase and frequency correct PWM mode can be defined by either
ICRn or OCRnA. The minimum resolution allowed is 2-bit (ICRn or OCRnA set to 0x0003), and124

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the maximum resolution is 16-bit (ICRn or OCRnA set to MAX). The PWM resolution in bits canbe calculated using the following equation:log ( TOP + 1 )R PFCPWM = ----------------------------------log ( 2 )In phase and frequency correct PWM mode the counter is incremented until the counter value
matches either the value in ICRn (WGMn3:0 = 8), or the value in OCRnA (WGMn3:0 = 9). The
counter has then reached the TOP and changes the count direction. The TCNTn value will beequal to TOP for one timer clock cycle. The timing diagram for the phase correct and frequency
correct PWM mode is shown on Figure 15-9. The figure shows phase and frequency correct
PWM mode when OCRnA or ICRn is used to define TOP. The TCNTn value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. The diagram includes noninverted and inverted PWM outputs. The small horizontal line marks on the TCNTn slopes represent compare matches between OCRnx and TCNTn. The OCnx Interrupt Flag will be set when acompare match occurs.
Figure 15-9. Phase and Frequency Correct PWM Mode, Timing Diagram
OCnA Interrupt Flag Set
or ICFn Interrupt Flag Set(Interrupt on TOP)

OCRnx/TOP Updateand
TOVn Interrupt Flag Set(Interrupt on Bottom)

TCNTn

OCnx

(COMnx1:0 = 2)

OCnx

(COMnx1:0 = 3)

Period1

2

3

4

The Timer/Counter Overflow Flag (TOVn) is set at the same timer clock cycle as the OCRnx
Registers are updated with the double buffer value (at BOTTOM). When either OCRnA or ICRn
is used for defining the TOP value, the OCnA or ICFn Flag set when TCNTn has reached TOP.
The Interrupt Flags can then be used to generate an interrupt each time the counter reaches theTOP or BOTTOM value.
When changing the TOP value the program must ensure that the new TOP value is higher or
equal to the value of all of the Compare Registers. If the TOP value is lower than any of theCompare Registers, a compare match will never occur between the TCNTn and the OCRnx.
As Figure 15-9 shows the output generated is, in contrast to the phase correct mode, symmetrical in all periods. Since the OCRnx Registers are updated at BOTTOM, the length of the risingand the falling slopes will always be equal. This gives symmetrical output pulses and is therefore
frequency correct.

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Using the ICRn Register for defining TOP works well when using fixed TOP values. By using
ICRn, the OCRnA Register is free to be used for generating a PWM output on OCnA. However,if the base PWM frequency is actively changed by changing the TOP value, using the OCRnA as
TOP is clearly a better choice due to its double buffer feature.
In phase and frequency correct PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM andan inverted PWM output can be generated by setting the COMnx1:0 to three (See Table 15-3 onpage 130). The actual OCnx value will only be visible on the port pin if the data direction for the
port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing)
the OCnx Register at the compare match between OCRnx and TCNTn when the counter increments, and clearing (or setting) the OCnx Register at compare match between OCRnx and
TCNTn when the counter decrements. The PWM frequency for the output when using phaseand frequency correct PWM can be calculated by the following equation:
f clk_I/O
f OCnxPFCPWM = ---------------------------2 ⋅ N ⋅ TOP
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).
The extreme values for the OCRnx Register represents special cases when generating a PWM
waveform output in the phase correct PWM mode. If the OCRnx is set equal to BOTTOM theoutput will be continuously low and if set equal to TOP the output will be set to high for noninverted PWM mode. For inverted PWM the output will have the opposite logic values. If OCR1A
is used to define the TOP value (WGM13:0 = 9) and COM1A1:0 = 1, the OC1A output will toggle
with a 50% duty cycle.

15.9

Timer/Counter Timing Diagrams
The Timer/Counter is a synchronous design and the timer clock (clkTn) is therefore shown as aclock enable signal in the following figures. The figures include information on when Interrupt
Flags are set, and when the OCRnx Register is updated with the OCRnx buffer value (only formodes utilizing double buffering). Figure 15-10 shows a timing diagram for the setting of OCFnx.
Figure 15-10. Timer/Counter Timing Diagram, Setting of OCFnx, no Prescaling
clkI/O
clkTn(clkI/O /1)

TCNTn
OCRnx

OCRnx - 1

OCRnx

OCRnx + 1

OCRnx + 2

OCRnx Value

OCFnx

Figure 15-11 shows the same timing data, but with the prescaler enabled.

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Figure 15-11. Timer/Counter Timing Diagram, Setting of OCFnx, with Prescaler (fclk_I/O/8)
clkI/O
clkTn(clkI/O /8)

TCNTn

OCRnx - 1

OCRnx

OCRnx

OCRnx + 1

OCRnx + 2

OCRnx Value

OCFnx

Figure 15-12 shows the count sequence close to TOP in various modes. When using phase andfrequency correct PWM mode the OCRnx Register is updated at BOTTOM. The timing diagrams
will be the same, but TOP should be replaced by BOTTOM, TOP-1 by BOTTOM+1 and so on.
The same renaming applies for modes that set the TOVn Flag at BOTTOM.
Figure 15-12. Timer/Counter Timing Diagram, no Prescaling
clkI/O
clkTn(clkI/O /1)

TCNTn(CTC and FPWM)

TCNTn(PC and PFC PWM)

TOP - 1TOP

BOTTOM

BOTTOM + 1

TOP - 1TOP

TOP - 1TOP - 2

TOVn (FPWM)
and ICFn (if used
as TOP)

OCRnx(Update at TOP)

Old OCRnx Value

New OCRnx Value

Figure 15-13 shows the same timing data, but with the prescaler enabled.

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Figure 15-13. Timer/Counter Timing Diagram, with Prescaler (fclk_I/O/8)
clkI/O
clkTn(clkI/O/8)

TCNTn(CTC and FPWM)

TCNTn(PC and PFC PWM)

TOP - 1TOP

BOTTOM

BOTTOM + 1

TOP - 1TOP

TOP - 1TOP - 2

TOVn (FPWM)
and ICF n (if used
as TOP)

OCRnx

Old OCRnx Value(Update at TOP)New OCRnx Value

15.10 16-bit Timer/Counter Register Description
15.10.1

Timer/Counter1 Control Register A – TCCR1A
Bit

7

6

5

4

3

2

1

COM1A1

COM1A0COM1B1COM1B0

COM1C1

COM1C0

WGM11

0
WGM10

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TCCR1A• Bit 7:6 – COMnA1:0: Compare Output Mode for Channel A• Bit 5:4 – COMnB1:0: Compare Output Mode for Channel B• Bit 3:2 – COMnC1:0: Compare Output Mode for Channel C
The COMnA1:0, COMnB1:0, and COMnC1:0 control the output compare pins (OCnA, OCnB,
and OCnC respectively) behavior. If one or both of the COMnA1:0 bits are written to one, theOCnA output overrides the normal port functionality of the I/O pin it is connected to. If one orboth of the COMnB1:0 bits are written to one, the OCnB output overrides the normal port functionality of the I/O pin it is connected to. If one or both of the COMnC1:0 bits are written to one,
the OCnC output overrides the normal port functionality of the I/O pin it is connected to. However, note that the Data Direction Register (DDR) bit corresponding to the OCnA, OCnB or
OCnC pin must be set in order to enable the output driver.
When the OCnA, OCnB or OCnC is connected to the pin, the function of the COMnx1:0 bits isdependent of the WGMn3:0 bits setting. Table 15-1 shows the COMnx1:0 bit functionality when
the WGMn3:0 bits are set to a normal or a CTC mode (non-PWM).

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Table 15-1.

Compare Output Mode, non-PWM

COMnA1/COMnB1/
COMnC1COMnA0/COMnB0/
COMnC000Normal port operation, OCnA/OCnB/OCnC
disconnected.

0

1

Toggle OCnA/OCnB/OCnC on compare match.

10

Clear OCnA/OCnB/OCnC on compare match(set output to low level).

1

1

Set OCnA/OCnB/OCnC on compare match (setoutput to high level).

Description

Table 15-2 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the fast
PWM mode.
Table 15-2.

Compare Output Mode, Fast PWM

COMnA1/COMnB1/
COMnC0COMnA0/COMnB0/
COMnC000Normal port operation, OCnA/OCnB/OCnC
disconnected.

0

1

WGM13:0 = 14 or 15: Toggle OC1A on Compare
Match, OC1B and OC1C disconnected (normal
port operation). For all other WGM1 settings,
normal port operation, OC1A/OC1B/OC1C
disconnected.

10

Clear OCnA/OCnB/OCnC on compare match,
set OCnA/OCnB/OCnC at TOP

1

1

Set OCnA/OCnB/OCnC on compare match,clear OCnA/OCnB/OCnC at TOP

Note:

Description

A special case occurs when OCRnA/OCRnB/OCRnC equals TOP and
COMnA1/COMnB1/COMnC1 is set. In this case the compare match is ignored, but the set or clear
is done at TOP. See “Fast PWM Mode” on page 96. for more details.

Table 15-3 shows the COMnx1:0 bit functionality when the WGMn3:0 bits are set to the phasecorrect and frequency correct PWM mode.

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Table 15-3.

Compare Output Mode, Phase Correct and Phase and Frequency Correct PWM

COMnA1/COMnB/
COMnC1COMnA0/COMnB0/
COMnC000Normal port operation, OCnA/OCnB/OCnC
disconnected.

0

1

WGM13:0 = 8, 9 10 or 11: Toggle OC1A on
Compare Match, OC1B and OC1C disconnected(normal port operation). For all other WGM1
settings, normal port operation,
OC1A/OC1B/OC1C disconnected.

10

Clear OCnA/OCnB/OCnC on compare match
when up-counting. Set OCnA/OCnB/OCnC on
compare match when downcounting.

1

1

Set OCnA/OCnB/OCnC on compare match when
up-counting. Clear OCnA/OCnB/OCnC on
compare match when downcounting.

Note:

Description

A special case occurs when OCRnA/OCRnB/OCRnC equals TOP and
COMnA1/COMnB1//COMnC1 is set. See “Phase Correct PWM Mode” on page 98. for moredetails.

• Bit 1:0 – WGMn1:0: Waveform Generation Mode
Combined with the WGMn3:2 bits found in the TCCRnB Register, these bits control the counting
sequence of the counter, the source for maximum (TOP) counter value, and what type of waveform generation to be used, see Table 15-4. Modes of operation supported by the Timer/Counter
unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode, and three typesof Pulse Width Modulation (PWM) modes. (See “Modes of Operation” on page 95.).

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Table 15-4.

Note:

Waveform Generation Mode Bit Description(1)

Mo
de

WGM
n3

WGM
n2
(CTCn
)

WGM
n1
(PWM
n1)

WGM
n0
(PWM
n0)

TOP

Update
of
OCRnx
at

0

0

0

0

0

Normal0xFFF
F

Immedi
ate

MAX

1

0

0

0

1

PWM, Phase Correct,
8-bit

0x00F
F

TOP

BOTTO
M

2

0

0

1

0

PWM, Phase Correct,
9-bit

0x01F
F

TOP

BOTTO
M

3

0

0

1

1

PWM, Phase Correct,
10-bit

0x03F
F

TOP

BOTTO
M

4

0

1

0

0

CTC

OCRn
A

Immedi
ate

MAX

5

0

1

0

1

Fast PWM, 8-bit

0x00F
F

TOP

TOP

6

0

1

1

0

Fast PWM, 9-bit

0x01F
F

TOP

TOP

7

0

1

1

1

Fast PWM, 10-bit

0x03F
F

TOP

TOP

8

1

0

0

0

PWM, Phase andFrequency Correct

ICRn

BOTTO
M

BOTTO
M

9

1

0

0

1

PWM, Phase andFrequency Correct

OCRn
A

BOTTO
M

BOTTO
M

10

1

0

1

0

PWM, Phase Correct

ICRn

TOP

BOTTO
M

11

1

0

1

1

PWM, Phase Correct

OCRn
A

TOP

BOTTO
M

12

1

1

0

0

CTC

ICRn

Immedi
ate

MAX

13

1

1

0

1

(Reserved)

–

–

–

14

1

1

1

0

Fast PWM

ICRn

TOP

TOP

15

1

1

1

1

Fast PWM

OCRn
A

TOP

TOP

Timer/Counter Modeof Operation

TOVn
Flag
Set on1. The CTCn and PWMn1:0 bit definition names are obsolete. Use the WGMn2:0 definitions. However, the functionality andlocation of these bits are compatible with previous versions of the timer.

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15.10.2

Timer/Counter1 Control Register B – TCCR1B
Bit

7

6

5

4

3

2

1

ICNC1

ICES1

–

WGM13

WGM12

CS12

CS11

0
CS10

Read/Write

R/W

R/W

R

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TCCR1B• Bit 7 – ICNCn: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture Noise Canceler. When the Noise Canceler isactivated, the input from the Input Capture Pin (ICPn) is filtered. The filter function requires four
successive equal valued samples of the ICPn pin for changing its output. The input capture is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
• Bit 6 – ICESn: Input Capture Edge SelectThis bit selects which edge on the Input Capture Pin (ICPn) that is used to trigger a capture
event. When the ICESn bit is written to zero, a falling (negative) edge is used as trigger, andwhen the ICESn bit is written to one, a rising (positive) edge will trigger the capture.
When a capture is triggered according to the ICESn setting, the counter value is copied into the
Input Capture Register (ICRn). The event will also set the Input Capture Flag (ICFn), and thiscan be used to cause an Input Capture Interrupt, if this interrupt is enabled.
When the ICRn is used as TOP value (see description of the WGMn3:0 bits located in the
TCCRnA and the TCCRnB Register), the ICPn is disconnected and consequently the input capture function is disabled.
• Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when TCCRnB is written.
• Bit 4:3 – WGMn3:2: Waveform Generation Mode
See TCCRnA Register description.
• Bit 2:0 – CSn2:0: Clock SelectThe three clock select bits select the clock source to be used by the Timer/Counter, see Figure14-1 and Figure 14-2.

Table 15-5.

132

Clock Select Bit Description

CSn2

CSn1

CSn0

0

0

0

No clock source. (Timer/Counter stopped)

0

0

1

clkI/O/1 (No prescaling

0

1

0

clkI/O/8 (From prescaler)

0

1

1

clkI/O/64 (From prescaler)

1

0

0

clkI/O/256 (From prescaler)

1

0

1

clkI/O/1024 (From prescaler)

1

1

0

External clock source on Tn pin. Clock on falling edge

1

1

1

External clock source on Tn pin. Clock on rising edge

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If external pin modes are used for the Timer/Countern, transitions on the Tn pin will clock thecounter even if the pin is configured as an output. This feature allows software control of thecounting.
15.10.3

Timer/Counter1 Control Register C – TCCR1C
Bit

7

6

5

4

3

2

1

FOC1A

FOC1B

FOC1C

–

–

–

–

0
–

Read/Write

W

W

W

R

R

R

R

R

Initial Value

0

0

0

0

0

0

0

0

TCCR1C• Bit 7 – FOCnA: Force Output Compare for Channel A• Bit 6 – FOCnB: Force Output Compare for Channel B• Bit 5 – FOCnC: Force Output Compare for Channel C
The FOCnA/FOCnB/FOCnC bits are only active when the WGMn3:0 bits specifies a non-PWM
mode. When writing a logical one to the FOCnA/FOCnB/FOCnC bit, an immediate compare
match is forced on the waveform generation unit. The OCnA/OCnB/OCnC output is changed
according to its COMnx1:0 bits setting. Note that the FOCnA/FOCnB/FOCnC bits are implemented as strobes. Therefore it is the value present in the COMnx1:0 bits that determine theeffect of the forced compare.
A FOCnA/FOCnB/FOCnC strobe will not generate any interrupt nor will it clear the timer in Clear
Timer on Compare Match (CTC) mode using OCRnA as TOP.
The FOCnA/FOCnB/FOCnB bits are always read as zero.
• Bit 4:0 – Reserved Bits
These bits are reserved for future use. For ensuring compatibility with future devices, these bits
must be written to zero when TCCRnC is written.
15.10.4

Timer/Counter1 – TCNT1H and TCNT1L
Bit

7

6

5

4

3

2

1

0

TCNT1[15:8]

TCNT1H

TCNT1[7:0]

TCNT1L

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

The two Timer/Counter I/O locations (TCNTnH and TCNTnL, combined TCNTn) give directaccess, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To
ensure that both the high and low bytes are read and written simultaneously when the CPU
accesses these registers, the access is performed using an 8-bit temporary High Byte Register(TEMP). This temporary register is shared by all the other 16-bit registers. See “Accessing 16-bit
Registers” on page 109.
Modifying the counter (TCNTn) while the counter is running introduces a risk of missing a compare match between TCNTn and one of the OCRnx Registers.
Writing to the TCNTn Register blocks (removes) the compare match on the following timer clock
for all compare units.

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15.10.5

Output Compare Register 1 A – OCR1AH and OCR1AL
Bit

7

6

5

4

3

2

1

0

OCR1A[15:8]

OCR1AHOCR1A[7:0]

15.10.6

OCR1AL

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

3

2

1

0

Output Compare Register 1 B – OCR1BH and OCR1BL
Bit

7

6

5

4

OCR1B[15:8]

OCR1BHOCR1B[7:0]

15.10.7

OCR1BL

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

3

2

1

0

Output Compare Register 1 C – OCR1CH and OCR1CL
Bit

7

6

5

4

OCR1C[15:8]

OCR1CHOCR1C[7:0]

OCR1CL

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

The Output Compare Registers contain a 16-bit value that is continuously compared with thecounter value (TCNTn). A match can be used to generate an Output Compare interrupt, or to
generate a waveform output on the OCnx pin.
The Output Compare Registers are 16-bit in size. To ensure that both the high and low bytes are
written simultaneously when the CPU writes to these registers, the access is performed using an
8-bit temporary High Byte Register (TEMP). This temporary register is shared by all the other16-bit registers. See “Accessing 16-bit Registers” on page 109.
15.10.8

Input Capture Register 1 – ICR1H and ICR1L
Bit

7

6

5

4

3

2

1

0

ICR1[15:8]

ICR1H

ICR1[7:0]

ICR1L

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

IThe Input Capture is updated with the counter (TCNTn) value each time an event occurs on the
ICPn pin (or optionally on the Analog Comparator output for Timer/Counter1). The Input Capture
can be used for defining the counter TOP value.
The Input Capture Register is 16-bit in size. To ensure that both the high and low bytes are read
simultaneously when the CPU accesses these registers, the access is performed using an 8-bit
temporary High Byte Register (TEMP). This temporary register is shared by all the other 16-bit
registers. See “Accessing 16-bit Registers” on page 109.
15.10.9

Timer/Counter1 Interrupt Mask Register – TIMSK1
Bit

7

6

5

4

3

2

1

–

–

ICIE1

–

OCIE1COCIE1BOCIE1A0
TOIE1

Read/Write

R

R

R/W

R

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TIMSK1• Bit 5 – ICIEn: Timer/Countern, Input Capture Interrupt Enable
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When this bit is written to one, and the I-flag in the Status Register is set (interrupts globallyenabled), the Timer/Countern Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See “Interrupts” on page 63.) is executed when the ICFn Flag, located in TIFRn, is set.
Bit 3 – OCIEnC: Timer/Countern, Output Compare C Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globallyenabled), the Timer/Countern Output Compare C Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 63.) is executed when the OCFnC Flag, located in
TIFRn, is set.
• Bit 2 – OCIEnB: Timer/Countern, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globallyenabled), the Timer/Countern Output Compare B Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 63.) is executed when the OCFnB Flag, located in
TIFRn, is set.
• Bit 1 – OCIEnA: Timer/Countern, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globallyenabled), the Timer/Countern Output Compare A Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 63.) is executed when the OCFnA Flag, located in
TIFRn, is set.
• Bit 0 – TOIEn: Timer/Countern, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globallyenabled), the Timer/Countern Overflow interrupt is enabled. The corresponding Interrupt Vector(See “Interrupts” on page 63.) is executed when the TOVn Flag, located in TIFRn, is set.
15.10.10 Timer/Counter1 Interrupt Flag Register – TIFR1
Bit

7

6

5

4

3

2

1

–

–

ICF1

–

OCF1C

OCF1B

OCF1A

0
TOV1

Read/Write

R

R

R/W

R

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

TIFR1

• Bit 5 – ICFn: Timer/Countern, Input Capture Flag
This flag is set when a capture event occurs on the ICPn pin. When the Input Capture Register(ICRn) is set by the WGMn3:0 to be used as the TOP value, the ICFn Flag is set when the counter reaches the TOP value.
ICFn is automatically cleared when the Input Capture Interrupt Vector is executed. Alternatively,
ICFn can be cleared by writing a logic one to its bit location.
• Bit 3– OCFnC: Timer/Countern, Output Compare C Match Flag
This flag is set in the timer clock cycle after the counter (TCNTn) value matches the Output
Compare Register C (OCRnC).
Note that a Forced Output Compare (FOCnC) strobe will not set the OCFnC Flag.
OCFnC is automatically cleared when the Output Compare Match C Interrupt Vector is executed. Alternatively, OCFnC can be cleared by writing a logic one to its bit location.
• Bit 2 – OCFnB: Timer/Counter1, Output Compare B Match Flag

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This flag is set in the timer clock cycle after the counter (TCNTn) value matches the Output
Compare Register B (OCRnB).
Note that a Forced Output Compare (FOCnB) strobe will not set the OCFnB Flag.
OCFnB is automatically cleared when the Output Compare Match B Interrupt Vector is executed. Alternatively, OCFnB can be cleared by writing a logic one to its bit location.
• Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNTn value matches the Output Compare Register A (OCRnA).
Note that a Forced Output Compare (FOCnA) strobe will not set the OCFnA Flag.
OCFnA is automatically cleared when the Output Compare Match A Interrupt Vector is executed. Alternatively, OCFnA can be cleared by writing a logic one to its bit location.
• Bit 0 – TOVn: Timer/Countern, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In Normal and CTC modes,
the TOVn Flag is set when the timer overflows. Refer to Table 15-4 on page 131 for the TOVn
Flag behavior when using another WGMn3:0 bit setting.
TOVn is automatically cleared when the Timer/Countern Overflow Interrupt Vector is executed.
Alternatively, TOVn can be cleared by writing a logic one to its bit location.

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16. Serial Peripheral Interface – SPIThe Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between the
A T90 US B 82 /1 62 an d p er i ph e r al de v ic e s o r be twe e n s ev e r al AV R d ev i c e s. The
AT90USB82/162 SPI includes the following features:• Full-duplex, Three-wire Synchronous Data Transfer• Master or Slave Operation• LSB First or MSB First Data Transfer• Seven Programmable Bit Rates• End of Transmission Interrupt Flag
• Write Collision Flag Protection• Wake-up from Idle Mode
• Double Speed (CK/2) Master SPI Mode
USART can also be used in Master SPI mode, see “USART in SPI Mode” on page 173.
The Power Reduction SPI bit, PRSPI, in “Power Reduction Register 0 - PRR0” on page 43 on
page 50 must be written to zero to enable SPI module.
Figure 16-1. SPI Block Diagram(1)

SPI2X

SPI2X

DIVIDER
/2/4/8/16/32/64/128

Note:

1. Refer to Figure 1-1 on page 3, and Table 11-6 on page 77 for SPI pin placement.

The interconnection between Master and Slave CPUs with SPI is shown in Figure 16-2. The system consists of two shift Registers, and a Master clock generator. The SPI Master initiates thecommunication cycle when pulling low the Slave Select SS pin of the desired Slave. Master and
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Slave prepare the data to be sent in their respective shift Registers, and the Master generates
the required clock pulses on the SCK line to interchange data. Data is always shifted from Master to Slave on the Master Out – Slave In, MOSI, line, and from Slave to Master on the Master In– Slave Out, MISO, line. After each data packet, the Master will synchronize the Slave by pullinghigh the Slave Select, SS, line.
When configured as a Master, the SPI interface has no automatic control of the SS line. This
must be handled by user software before communication can start. When this is done, writing abyte to the SPI Data Register starts the SPI clock generator, and the hardware shifts the eightbits into the Slave. After shifting one byte, the SPI clock generator stops, setting the end of
Transmission Flag (SPIF). If the SPI Interrupt Enable bit (SPIE) in the SPCR Register is set, aninterrupt is requested. The Master may continue to shift the next byte by writing it into SPDR, or
signal the end of packet by pulling high the Slave Select, SS line. The last incoming byte will be
kept in the Buffer Register for later use.
When configured as a Slave, the SPI interface will remain sleeping with MISO tri-stated as longas the SS pin is driven high. In this state, software may update the contents of the SPI Data
Register, SPDR, but the data will not be shifted out by incoming clock pulses on the SCK pin
until the SS pin is driven low. As one byte has been completely shifted, the end of Transmission
Flag, SPIF is set. If the SPI Interrupt Enable bit, SPIE, in the SPCR Register is set, an interrupt
is requested. The Slave may continue to place new data to be sent into SPDR before reading
the incoming data. The last incoming byte will be kept in the Buffer Register for later use.
Figure 16-2. SPI Master-slave Interconnection

SHIFT
ENABLEThe system is single buffered in the transmit direction and double buffered in the receive direction. This means that bytes to be transmitted cannot be written to the SPI Data Register before
the entire shift cycle is completed. When receiving data, however, a received character must beread from the SPI Data Register before the next character has been completely shifted in. Otherwise, the first byte is lost.
In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure
correct sampling of the clock signal, the frequency of the SPI clock should never exceed fosc/4.

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When the SPI is enabled, the data direction of the MOSI, MISO, SCK, and SS pins is overridden
according to Table 16-1. For more details on automatic port overrides, refer to “Alternate Port
Functions” on page 72.
Table 16-1.

SPI Pin Overrides(1)PinDirection, Master SPI

Direction, Slave SPI

MOSIUser Defined

Input

MISO

Input

User Defined

SCK

User Defined

Input

SS

User Defined

Input

Note:

1. See “Alternate Functions of Port B” on page 74 for a detailed description of how to define thedirection of the user defined SPI pins.

The following code examples show how to initialize the SPI as a Master and how to perform asimple transmission. DDR_SPI in the examples must be replaced by the actual Data Direction
Register controlling the SPI pins. DD_MOSI, DD_MISO and DD_SCK must be replaced by theactual data direction bits for these pins. E.g. if MOSI is placed on pin PB5, replace DD_MOSI
with DDB5 and DDR_SPI with DDRB.

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Assembly Code Example(1)SPI_MasterInit:; Set MOSI and SCK output, all others input
ldi

r17,(1<<DD_MOSI)|(1<<DD_SCK)

out

DDR_SPI,r17; Enable SPI, Master, set clock rate fck/16
ldi

r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)out

SPCR,r17

ret
SPI_MasterTransmit:; Start transmission of data (r16)outSPDR,r16

Wait_Transmit:; Wait for transmission complete
sbis SPSR,SPIF
rjmp Wait_Transmit
ret

C Code Example(1)void SPI_MasterInit(void){/* Set MOSI and SCK output, all others input */DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);/* Enable SPI, Master, set clock rate fck/16 */SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);}
void SPI_MasterTransmit(char cData){/* Start transmission */SPDR = cData;/* Wait for transmission complete */while(!(SPSR & (1<<SPIF)))
;
}
Note:

140

1. See “About Code Examples” on page 7.

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The following code examples show how to initialize the SPI as a Slave and how to perform asimple reception.
Assembly Code Example(1)SPI_SlaveInit:; Set MISO output, all others input
ldi

r17,(1<<DD_MISO)

out

DDR_SPI,r17; Enable SPI
ldi

r17,(1<<SPE)

out

SPCR,r17

ret
SPI_SlaveReceive:; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive; Read received data and returnin

r16,SPDRret

C Code Example(1)void SPI_SlaveInit(void){/* Set MISO output, all others input */DDR_SPI = (1<<DD_MISO);/* Enable SPI */SPCR = (1<<SPE);}char SPI_SlaveReceive(void){/* Wait for reception complete */while(!(SPSR & (1<<SPIF)));/* Return Data Register */return SPDR;
}
Note:

16.1
16.1.1

1. See “About Code Examples” on page 7.

SS Pin Functionality
Slave Mode
When the SPI is configured as a Slave, the Slave Select (SS) pin is always input. When SS isheld low, the SPI is activated, and MISO becomes an output if configured so by the user. Allother pins are inputs. When SS is driven high, all pins are inputs, and the SPI is passive, which
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means that it will not receive incoming data. Note that the SPI logic will be reset once the SS pin
is driven high.
The SS pin is useful for packet/byte synchronization to keep the slave bit counter synchronouswith the master clock generator. When the SS pin is driven high, the SPI slave will immediately
reset the send and receive logic, and drop any partially received data in the Shift Register.
16.1.2Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine thedirection of the SS pin.
If SS is configured as an output, the pin is a general output pin which does not affect the SPI
system. Typically, the pin will be driving the SS pin of the SPI Slave.
If SS is configured as an input, it must be held high to ensure Master SPI operation. If theSS pin is driven low by peripheral circuitry when the SPI is configured as a Master with the SS
pin defined as an input, the SPI system interprets this as another master selecting the SPI as aslave and starting to send data to it. To avoid bus contention, the SPI system takes the following
actions:
1. The MSTR bit in SPCR is cleared and the SPI system becomes a Slave. As a result of
the SPI becoming a Slave, the MOSI and SCK pins become inputs.
2. The SPIF Flag in SPSR is set, and if the SPI interrupt is enabled, and the I-bit in SREG
is set, the interrupt routine will be executed.
Thus, when interrupt-driven SPI transmission is used in Master mode, and there exists a possibility that SS is driven low, the interrupt should always check that the MSTR bit is still set. If the
MSTR bit has been cleared by a slave select, it must be set by the user to re-enable SPI Mastermode.

16.1.3

SPI Control Register – SPCR
Bit

7

6

5

4

3

2

1

SPIE

SPE

DORD

MSTR

CPOL

CPHA

SPR1

0
SPR0

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

SPCR

• Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and the if
the Global Interrupt Enable bit in SREG is set.
• Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI
operations.
• Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first.
When the DORD bit is written to zero, the MSB of the data word is transmitted first.
• Bit 4 – MSTR: Master/Slave SelectThis bit selects Master SPI mode when written to one, and Slave SPI mode when written logic
zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared,

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and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Master mode.
• Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is low
when idle. Refer to Figure 16-3 and Figure 16-4 for an example. The CPOL functionality is summarized below:
Table 16-2.

CPOL Functionality
CPOL

Leading Edge

Trailing Edge0

Rising

Falling1

Falling

Rising• Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or
trailing (last) edge of SCK. Refer to Figure 16-3 and Figure 16-4 for an example. The CPOL
functionality is summarized below:
Table 16-3.

CPHA Functionality
CPHA

Leading Edge

Trailing Edge

0

Sample

Setup

1

Setup

Sample• Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0 haveno effect on the Slave. The relationship between SCK and the Oscillator Clock frequency fosc isshown in the following table:
Table 16-4.

16.1.4

Relationship Between SCK and the Oscillator Frequency

SPI2X

SPR1

SPR0

0

0

0

0

0

1

0

1

0

0

1

1

1

0

0

1

0

1

1

1

0

1

1

1

SCK Frequency

fosc/4
fosc/16
fosc/64
fosc/128
fosc/2
fosc/8
fosc/32
fosc/64

SPI Status Register – SPSR
Bit

7

6

5

4

3

2

1

SPIF

WCOL

–

–

–

–

–

0
SPI2X

Read/Write

R

R

R

R

R

R

R

R/W

Initial Value

0

0

0

0

0

0

0

0

SPSR

• Bit 7 – SPIF: SPI Interrupt Flag

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When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in
SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI isin Master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing thecorresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the
SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
• Bit 6 – WCOL: Write COLlision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The
WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set,
and then accessing the SPI Data Register.
• Bit 5..1 – Res: Reserved Bits
These bits are reserved bits in the AT90USB82/162 and will always read as zero.
• Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI
is in Master mode (see Table 16-4). This means that the minimum SCK period will be two CPU
clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fosc/4
or lower.
The SPI interface on the AT90USB82/162 is also used for program memory and EEPROM
downloading or uploading. See page 257 for serial programming and verification.
16.1.5

SPI Data Register – SPDR
Bit

7

6

5

4

3

2

1

0

MSB

LSB

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

X

X

X

X

X

X

X

X

SPDR
Undefined

The SPI Data Register is a read/write register used for data transfer between the Register Fileand the SPI Shift Register. Writing to the register initiates data transmission. Reading the register causes the Shift Register Receive buffer to be read.

16.2

Data Modes
There are four combinations of SCK phase and polarity with respect to serial data, which are
determined by control bits CPHA and CPOL. The SPI data transfer formats are shown in Figure16-3 and Figure 16-4. Data bits are shifted out and latched in on opposite edges of the SCK signal, ensuring sufficient time for data signals to stabilize. This is clearly seen by summarizing
Table 16-2 and Table 16-3, as done below:

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Table 16-5.

CPOL Functionality
Leading Edge

Trailing eDge

SPI Mode

CPOL=0, CPHA=0

Sample (Rising)

Setup (Falling)

0

CPOL=0, CPHA=1

Setup (Rising)

Sample (Falling)

1

CPOL=1, CPHA=0

Sample (Falling)

Setup (Rising)

2

CPOL=1, CPHA=1

Setup (Falling)

Sample (Rising)3

Figure 16-3. SPI Transfer Format with CPHA = 0
SCK (CPOL = 0)
mode 0SCK (CPOL = 1)
mode 2
SAMPLE I
MOSI/MISOCHANGE 0
MOSI PIN
CHANGE 0
MISO PINSS

MSB first (DORD = 0) MSB
LSB first (DORD = 1) LSB

Bit 6
Bit 1

Bit 5
Bit 2

Bit 4
Bit 3

Bit 3
Bit 4

Bit 2
Bit 5

Bit 1
Bit 6

LSB
MSB

Figure 16-4. SPI Transfer Format with CPHA = 1
SCK (CPOL = 0)
mode 1
SCK (CPOL = 1)
mode 3
SAMPLE I
MOSI/MISOCHANGE 0
MOSI PIN
CHANGE 0
MISO PINSS

MSB first (DORD = 0)
LSB first (DORD = 1)

MSB
LSB

Bit 6
Bit 1

Bit 5
Bit 2

Bit 4
Bit 3

Bit 3
Bit 4

Bit 2
Bit 5

Bit 1
Bit 6

LSB
MSB

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17. USARTThe Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) is ahighly flexible serial communication device. The main features are:• Full Duplex Operation (Independent Serial Receive and Transmit Registers)• Asynchronous or Synchronous Operation• Flow control CTS/RTS signals hardware management• Master or Slave Clocked Synchronous Operation• High Resolution Baud Rate Generator• Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits
• Odd or Even Parity Generation and Parity Check Supported by Hardware• Data OverRun Detection• Framing Error Detection• Noise Filtering Includes False Start Bit Detection and Digital Low Pass Filter• Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete• Multi-processor Communication Mode
• Double Speed Asynchronous Communication Mode

17.1

Overview
A simplified block diagram of the USART Transmitter is shown in Figure 17-1 on page 147. CPUaccessible I/O Registers and I/O pins are shown in bold.

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Figure 17-1. USART Block Diagram(1)Clock Generator
UBRR[H:L]

OSC

BAUD RATE GENERATORSYNC LOGICPINCONTROL

XCKTransmitter
TX
CONTROL

UDR (Transmit)

DATA BUSPARITY
GENERATOR
TxD

Receiver

UCSRA

Note:

PIN
CONTROL

TRANSMIT SHIFT REGISTERCLOCKRECOVERYRXCONTROLRECEIVE SHIFT REGISTERDATARECOVERYPIN
CONTROL

UDR (Receive)

PARITYCHECKER

UCSRB

RxD

UCSRC

1. See Figure 1-1 on page 3, Table 11-9 on page 79 and for USART pin placement.

The dashed boxes in the block diagram separate the three main parts of the USART (listed fromthe top): Clock Generator, Transmitter and Receiver. Control Registers are shared by all units.
The Clock Generation logic consists of synchronization logic for external clock input used bysynchronous slave operation, and the baud rate generator. The XCKn (Transfer Clock) pin is
only used by synchronous transfer mode. The Transmitter consists of a single write buffer, aserial Shift Register, Parity Generator and Control logic for handling different serial frame formats. The write buffer allows a continuous transfer of data without any delay between frames.
The Receiver is the most complex part of the USART module due to its clock and data recovery
units. The recovery units are used for asynchronous data reception. In addition to the recovery
units, the Receiver includes a Parity Checker, Control logic, a Shift Register and a two level
receive buffer (UDRn). The Receiver supports the same frame formats as the Transmitter, andcan detect Frame Error, Data OverRun and Parity Errors.

17.2

Clock Generation
The Clock Generation logic generates the base clock for the Transmitter and Receiver. The
USARTn supports four modes of clock operation: Normal asynchronous, Double Speed asynchronous, Master synchronous and Slave synchronous mode. The UMSELn bit in USART
Control and Status Register C (UCSRnC) selects between asynchronous and synchronous
operation. Double Speed (asynchronous mode only) is controlled by the U2Xn found in the
UCSRnA Register. When using synchronous mode (UMSELn = 1), the Data Direction Register

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for the XCKn pin (DDR_XCKn) controls whether the clock source is internal (Master mode) or
external (Slave mode). The XCKn pin is only active when using synchronous mode.
Figure 17-2 shows a block diagram of the clock generation logic.
Figure 17-2. Clock Generation Logic, Block Diagram
UBRR

U2X

fosc
Prescaling
Down-Counter

UBRR+1

/2

/4

/2

0
1
0

OSC
DDR_XCK

xcki
XCK
Pin

Sync
RegisterEdge
Detector

0

UCPOL

txclk

UMSEL

1

xcko

DDR_XCK

1

1
0

rxclk

Signal description:
txclk

Transmitter clock (Internal Signal).

rxclk

Receiver base clock (Internal Signal).

xcki
operation.

17.2.1

Input from XCK pin (internal Signal). Used for synchronous slave

xcko

Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.

fOSC

XTAL pin frequency (System Clock).

Internal Clock Generation – The Baud Rate Generator
Internal clock generation is used for the asynchronous and the synchronous master modes ofoperation. The description in this section refers to Figure 17-2.
The USART Baud Rate Register (UBRRn) and the down-counter connected to it function as aprogrammable prescaler or baud rate generator. The down-counter, running at system clock(fosc), is loaded with the UBRRn value each time the counter has counted down to zero or when
the UBRRLn Register is written. A clock is generated each time the counter reaches zero. This
clock is the baud rate generator clock output (= fosc/(UBRRn+1)). The Transmitter divides thebaud rate generator clock output by 2, 8 or 16 depending on mode. The baud rate generator output is used directly by the Receiver’s clock and data recovery units. However, the recovery units
use a state machine that uses 2, 8 or 16 states depending on mode set by the state of the
UMSELn, U2Xn and DDR_XCKn bits.

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Table 17-1 contains equations for calculating the baud rate (in bits per second) and for calculating the UBRRn value for each mode of operation using an internally generated clock source.
Table 17-1.

Equations for Calculating Baud Rate Register Setting
Equation for Calculating Baud Rate(1)Operating Mode

Equation for Calculating UBRR Valuef OSC
UBRRn = ------------------------ – 1
16BAUD
Asynchronous Normal mode
(U2Xn = 0)f OSC
BAUD = -----------------------------------------16 ( UBRRn + 1 )f OSC
UBRRn = -------------------- – 1
8BAUD
Asynchronous Double Speedmode (U2Xn = 1)

f OSC
BAUD = --------------------------------------8 ( UBRRn + 1 )f OSC
UBRRn = -------------------- – 1
2BAUD
f OSC
BAUD = --------------------------------------2 ( UBRRn + 1 )Synchronous Master mode

Note:

1. The baud rate is defined to be the transfer rate in bit per second (bps)

BAUD

Baud rate (in bits per second, bps)

fOSC

System Oscillator clock frequency

UBRRn

Contents of the UBRRHn and UBRRLn Registers, (0-4095)

Some examples of UBRRn values for some system clock frequencies are found in Table 17-9 on
page 170.
17.2.2

Double Speed Operation (U2Xn)
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. Setting this bit only has
effect for the asynchronous operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling
the transfer rate for asynchronous communication. Note however that the Receiver will in thiscase only use half the number of samples (reduced from 16 to 8) for data sampling and clock
recovery, and therefore a more accurate baud rate setting and system clock are required when
this mode is used. For the Transmitter, there are no downsides.

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17.2.3

External Clock
External clocking is used by the synchronous slave modes of operation. The description in thissection refers to Figure 17-2 for details.
External clock input from the XCKn pin is sampled by a synchronization register to minimize thechance of meta-stability. The output from the synchronization register must then pass throughan edge detector before it can be used by the Transmitter and Receiver. This process introduces a two CPU clock period delay and therefore the maximum external XCKn clock frequency
is limited by the following equation:
f OSC
f XCK < ----------4
Note that fosc depends on the stability of the system clock source. It is therefore recommended to
add some margin to avoid possible loss of data due to frequency variations.

17.2.4

Synchronous Clock Operation
When synchronous mode is used (UMSELn = 1), the XCKn pin will be used as either clock input(Slave) or clock output (Master). The dependency between the clock edges and data samplingor data change is the same. The basic principle is that data input (on RxDn) is sampled at the
opposite XCKn clock edge of the edge the data output (TxDn) is changed.
Figure 17-3. Synchronous Mode XCKn Timing.
UCPOL = 1

XCK

RxD / TxD
SampleUCPOL = 0

XCKRxD / TxD
SampleThe UCPOLn bit UCRSC selects which XCKn clock edge is used for data sampling and which isused for data change. As Figure 17-3 shows, when UCPOLn is zero the data will be changed atrising XCKn edge and sampled at falling XCKn edge. If UCPOLn is set, the data will be changed
at falling XCKn edge and sampled at rising XCKn edge.

17.3

Frame Formats
A serial frame is defined to be one character of data bits with synchronization bits (start and stopbits), and optionally a parity bit for error checking. The USART accepts all 30 combinations of
the following as valid frame formats:• 1 start bit• 5, 6, 7, 8, or 9 data bits
• no, even or odd parity bit• 1 or 2 stop bits

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A frame starts with the start bit followed by the least significant data bit. Then the next data bits,
up to a total of nine, are succeeding, ending with the most significant bit. If enabled, the parity bit
is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it canbe directly followed by a new frame, or the communication line can be set to an idle (high) state.
Figure 17-4 illustrates the possible combinations of the frame formats. Bits inside brackets are
optional.
Figure 17-4. Frame Formats
FRAME(IDLE)

St

0

1

2

3

4

[5]

[6]

St

Start bit, always low.

(n)

Data bits (0 to 8).

P

Parity bit. Can be odd or even.

Sp

Stop bit, always high.

IDLE
must be

[7]

[8]

[P]

Sp1 [Sp2](St / IDLE)

No transfers on the communication line (RxDn or TxDn). An IDLE linehigh.

The frame format used by the USART is set by the UCSZn2:0, UPMn1:0 and USBSn bits in
UCSRnB and UCSRnC. The Receiver and Transmitter use the same setting. Note that changing
the setting of any of these bits will corrupt all ongoing communication for both the Receiver andTransmitter.
The USART Character SiZe (UCSZn2:0) bits select the number of data bits in the frame. The
USART Parity mode (UPMn1:0) bits enable and set the type of parity bit. The selection between
one or two stop bits is done by the USART Stop Bit Select (USBSn) bit. The Receiver ignores
the second stop bit. An FE (Frame Error) will therefore only be detected in the cases where thefirst stop bit is zero.
17.3.1

Parity Bit Calculation
The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is used, theresult of the exclusive or is inverted. The relation between the parity bit and data bits is asfollows::
P even = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 0
P odd = d n – 1 ⊕ … ⊕ d 3 ⊕ d 2 ⊕ d 1 ⊕ d 0 ⊕ 1
Peven

Parity bit using even parity

odd

Parity bit using odd parity

Pdn

Data bit n of the character

If used, the parity bit is located between the last data bit and first stop bit of a serial frame.

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17.4

USART Initialization
The USART has to be initialized before any communication can take place. The initialization process normally consists of setting the baud rate, setting frame format and enabling theTransmitter or the Receiver depending on the usage. For interrupt driven USART operation, theGlobal Interrupt Flag should be cleared (and interrupts globally disabled) when doing theinitialization.
Before doing a re-initialization with changed baud rate or frame format, be sure that there are no
ongoing transmissions during the period the registers are changed. The TXCn Flag can be used
to check that the Transmitter has completed all transfers, and the RXC Flag can be used tocheck that there are no unread data in the receive buffer. Note that the TXCn Flag must be
cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C function that are equal in functionality. The examples assume asynchronous operation using polling(no interrupts enabled) and a fixed frame format. The baud rate is given as a function parameter.
For the assembly code, the baud rate parameter is assumed to be stored in the r17:r16
Registers.
Assembly Code Example(1)USART_Init:; Set baud rateout

UBRRHn, r17

out

UBRRLn, r16; Enable receiver and transmitter
ldi

r16, (1<<RXENn)|(1<<TXENn)

out

UCSRnB,r16; Set frame format: 8data, 2stop bit
ldi

r16, (1<<USBSn)|(3<<UCSZn0)out

UCSRnC,r16

ret

C Code Example(1)void USART_Init( unsigned int baud ){/* Set baud rate */UBRRHn = (unsigned char)(baud>>8);
UBRRLn = (unsigned char)baud;/* Enable receiver and transmitter */UCSRnB = (1<<RXENn)|(1<<TXENn);/* Set frame format: 8data, 2stop bit */UCSRnC = (1<<USBSn)|(3<<UCSZn0);}
Note:

1. See “About Code Examples” on page 7.

More advanced initialization routines can be made that include frame format as parameters, disable interrupts and so on. However, many applications use a fixed setting of the baud andcontrol registers, and for these types of applications the initialization code can be placed directlyin the main routine, or be combined with initialization code for other I/O modules.

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17.5

Data Transmission – The USART Transmitter
The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSRnB
Register. When the Transmitter is enabled, the normal port operation of the TxDn pin is overridden by the USART and given the function as the Transmitter’s serial output. The baud rate,
mode of operation and frame format must be set up once before doing any transmissions. If synchronous operation is used, the clock on the XCKn pin will be overridden and used astransmission clock.

17.5.1

Sending Frames with 5 to 8 Data Bit
A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The
CPU can load the transmit buffer by writing to the UDRn I/O location. The buffered data in thetransmit buffer will be moved to the Shift Register when the Shift Register is ready to send a newframe. The Shift Register is loaded with new data if it is in idle state (no ongoing transmission) or
immediately after the last stop bit of the previous frame is transmitted. When the Shift Register isloaded with new data, it will transfer one complete frame at the rate given by the Baud Register,
U2Xn bit or by XCKn depending on mode of operation.
The following code examples show a simple USART transmit function based on polling of theData Register Empty (UDREn) Flag. When using frames with less than eight bits, the most significant bits written to the UDRn are ignored. The USART has to be initialized before the function
can be used. For the assembly code, the data to be sent is assumed to be stored in Register
R16
Assembly Code Example(1)USART_Transmit:; Wait for empty transmit buffer
sbis UCSRnA,UDREn
rjmp USART_Transmit; Put data (r16) into buffer, sends the data
out

UDRn,r16

ret

C Code Example(1)void USART_Transmit( unsigned char data ){/* Wait for empty transmit buffer */while ( !( UCSRnA & (1<<UDREn)) );/* Put data into buffer, sends the data */UDRn = data;}
Note:

1. See “About Code Examples” on page 7.

The function simply waits for the transmit buffer to be empty by checking the UDREn Flag,
before loading it with new data to be transmitted. If the Data Register Empty interrupt is utilized,
the interrupt routine writes the data into the buffer.
17.5.2

Sending Frames with 9 Data Bit
If 9-bit characters are used (UCSZn = 7), the ninth bit must be written to the TXB8 bit in
UCSRnB before the low byte of the character is written to UDRn. The following code examples
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show a transmit function that handles 9-bit characters. For the assembly code, the data to besent is assumed to be stored in registers R17:R16.
Assembly Code Example(1)(2)
USART_Transmit:; Wait for empty transmit buffer
sbis UCSRnA,UDREn
rjmp USART_Transmit; Copy 9th bit from r17 to TXB8
cbi

UCSRnB,TXB8

sbrc r17,0
sbi

UCSRnB,TXB8; Put LSB data (r16) into buffer, sends the data
out

UDRn,r16

ret

C Code Example(1)(2)void USART_Transmit( unsigned int data ){/* Wait for empty transmit buffer */while ( !( UCSRnA & (1<<UDREn))) );/* Copy 9th bit to TXB8 */UCSRnB &= ~(1<<TXB8);
if ( data & 0x0100 )UCSRnB |= (1<<TXB8);/* Put data into buffer, sends the data */UDRn = data;}
Notes:

1. These transmit functions are written to be general functions. They can be optimized if the contents of the UCSRnB is static. For example, only the TXB8 bit of the UCSRnB Register is used
after initialization.
2. See “About Code Examples” on page 7.

The ninth bit can be used for indicating an address frame when using multi processor communication mode or for other protocol handling as for example synchronization.
17.5.3

Transmitter Flags and Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register Empty(UDREn) and Transmit Complete (TXCn). Both flags can be used for generating interrupts.
The Data Register Empty (UDREn) Flag indicates whether the transmit buffer is ready to receive
new data. This bit is set when the transmit buffer is empty, and cleared when the transmit buffer
contains data to be transmitted that has not yet been moved into the Shift Register. For compatibility with future devices, always write this bit to zero when writing the UCSRnA Register.
When the Data Register Empty Interrupt Enable (UDRIEn) bit in UCSRnB is written to one, the
USART Data Register Empty Interrupt will be executed as long as UDREn is set (provided that
global interrupts are enabled). UDREn is cleared by writing UDRn. When interrupt-driven datatransmission is used, the Data Register Empty interrupt routine must either write new data to

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UDRn in order to clear UDREn or disable the Data Register Empty interrupt, otherwise a newinterrupt will occur once the interrupt routine terminates.
The Transmit Complete (TXCn) Flag bit is set one when the entire frame in the Transmit Shift
Register has been shifted out and there are no new data currently present in the transmit buffer.
The TXCn Flag bit is automatically cleared when a transmit complete interrupt is executed, or it
can be cleared by writing a one to its bit location. The TXCn Flag is useful in half-duplex communication interfaces (like the RS-485 standard), where a transmitting application must enter
receive mode and free the communication bus immediately after completing the transmission.
When the Transmit Compete Interrupt Enable (TXCIEn) bit in UCSRnB is set, the USARTTransmit Complete Interrupt will be executed when the TXCn Flag becomes set (provided that
global interrupts are enabled). When the transmit complete interrupt is used, the interrupt handling routine does not have to clear the TXCn Flag, this is done automatically when the interrupt
is executed.
17.5.4

Parity Generator
The Parity Generator calculates the parity bit for the serial frame data. When parity bit is enabled(UPMn1 = 1), the transmitter control logic inserts the parity bit between the last data bit and thefirst stop bit of the frame that is sent.

17.5.5

Disabling the Transmitter
The disabling of the Transmitter (setting the TXEN to zero) will not become effective until ongoing and pending transmissions are completed, i.e., when the Transmit Shift Register andTransmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter
will no longer override the TxDn pin.

17.6

Data Reception – The USART Receiver
The USART Receiver is enabled by writing the Receive Enable (RXENn) bit in the
UCSRnB Register to one. When the Receiver is enabled, the normal pin operation of the RxDn
pin is overridden by the USART and given the function as the Receiver’s serial input. The baudrate, mode of operation and frame format must be set up once before any serial reception canbe done. If synchronous operation is used, the clock on the XCKn pin will be used as transfer
clock.

17.6.1

Receiving Frames with 5 to 8 Data Bits
The Receiver starts data reception when it detects a valid start bit. Each bit that follows the start
bit will be sampled at the baud rate or XCKn clock, and shifted into the Receive Shift Register
until the first stop bit of a frame is received. A second stop bit will be ignored by the Receiver.
When the first stop bit is received, i.e., a complete serial frame is present in the Receive Shift
Register, the contents of the Shift Register will be moved into the receive buffer. The receive
buffer can then be read by reading the UDRn I/O location.
The following code example shows a simple USART receive function based on polling of theReceive Complete (RXCn) Flag. When using frames with less than eight bits the most significant

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bits of the data read from the UDRn will be masked to zero. The USART has to be initialized
before the function can be used.
Assembly Code Example(1)USART_Receive:; Wait for data to be received
sbis UCSRnA, RXCn
rjmp USART_Receive; Get and return received data from bufferinr16, UDRnret

C Code Example(1)unsigned char USART_Receive( void ){/* Wait for data to be received */while ( !(UCSRnA & (1<<RXCn)) );/* Get and return received data from buffer */return UDRn;}
Note:

1. See “About Code Examples” on page 7.

The function simply waits for data to be present in the receive buffer by checking the RXCn Flag,
before reading the buffer and returning the value.
17.6.2

Receiving Frames with 9 Data Bits
If 9-bit characters are used (UCSZn=7) the ninth bit must be read from the RXB8n bit in
UCSRnB before reading the low bits from the UDRn. This rule applies to the FEn, DORn and
UPEn Status Flags as well. Read status from UCSRnA, then data from UDRn. Reading the
UDRn I/O location will change the state of the receive buffer FIFO and consequently the TXB8n,
FEn, DORn and UPEn bits, which all are stored in the FIFO, will change.
The following code example shows a simple USART receive function that handles both nine bit
characters and the status bits.

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Assembly Code Example(1)USART_Receive:; Wait for data to be received
sbis UCSRnA, RXCn
rjmp USART_Receive; Get status and 9th bit, then data from bufferinr18, UCSRnA

in

r17, UCSRnB

in

r16, UDRn; If error, return -1
andi r18,(1<<FEn)|(1<<DORn)|(1<<UPEn)
breq USART_ReceiveNoErrorldir17, HIGH(-1)

ldir16, LOW(-1)

USART_ReceiveNoError:; Filter the 9th bit, then return
lsr

r17

andi r17, 0x01
ret

C Code Example(1)unsigned int USART_Receive( void ){unsigned char status, resh, resl;/* Wait for data to be received */while ( !(UCSRnA & (1<<RXCn)) );/* Get status and 9th bit, then data *//* from buffer */status = UCSRnA;
resh = UCSRnB;
resl = UDRn;/* If error, return -1 */if ( status & (1<<FEn)|(1<<DORn)|(1<<UPEn) )return -1;/* Filter the 9th bit, then return */resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);}
Note:

1. See “About Code Examples” on page 7.

The receive function example reads all the I/O Registers into the Register File before any computation is done. This gives an optimal receive buffer utilization since the buffer location read will
be free to accept new data as early as possible.

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17.6.3

Receive Compete Flag and Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXCn) Flag indicates if there are unread data present in the receive buffer. This flag is one when unread data exist in the receive buffer, and zero when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled (RXENn = 0),
the receive buffer will be flushed and consequently the RXCn bit will become zero.
When the Receive Complete Interrupt Enable (RXCIEn) in UCSRnB is set, the USART Receive
Complete interrupt will be executed as long as the RXCn Flag is set (provided that global interrupts are enabled). When interrupt-driven data reception is used, the receive complete routine
must read the received data from UDRn in order to clear the RXCn Flag, otherwise a new interrupt will occur once the interrupt routine terminates.

17.6.4

Receiver Error Flags
The USART Receiver has three Error Flags: Frame Error (FEn), Data OverRun (DORn) andParity Error (UPEn). All can be accessed by reading UCSRnA. Common for the Error Flags isthat they are located in the receive buffer together with the frame for which they indicate theerror status. Due to the buffering of the Error Flags, the UCSRnA must be read before thereceive buffer (UDRn), since reading the UDRn I/O location changes the buffer read location.
Another equality for the Error Flags is that they can not be altered by software doing a write to
the flag location. However, all flags must be set to zero when the UCSRnA is written for upward
compatibility of future USART implementations. None of the Error Flags can generate interrupts.
The Frame Error (FEn) Flag indicates the state of the first stop bit of the next readable frame
stored in the receive buffer. The FEn Flag is zero when the stop bit was correctly read (as one),and the FEn Flag will be one when the stop bit was incorrect (zero). This flag can be used for
detecting out-of-sync conditions, detecting break conditions and protocol handling. The FEn
Flag is not affected by the setting of the USBSn bit in UCSRnC since the Receiver ignores all,except for the first, stop bits. For compatibility with future devices, always set this bit to zero
when writing to UCSRnA.
The Data OverRun (DORn) Flag indicates data loss due to a receiver buffer full condition. A
Data OverRun occurs when the receive buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a new start bit is detected. If the DORn Flag is set there
was one or more serial frame lost between the frame last read from UDRn, and the next frame
read from UDRn. For compatibility with future devices, always write this bit to zero when writing
to UCSRnA. The DORn Flag is cleared when the frame received was successfully moved fromthe Shift Register to the receive buffer.
The Parity Error (UPEn) Flag indicates that the next frame in the receive buffer had a Parity
Error when received. If Parity Check is not enabled the UPEn bit will always be read zero. For
compatibility with future devices, always set this bit to zero when writing to UCSRnA. For moredetails see “Parity Bit Calculation” on page 151 and “Parity Checker” on page 158.

17.6.5

Parity Checker
The Parity Checker is active when the high USART Parity mode (UPMn1) bit is set. Type of Parity Check to be performed (odd or even) is selected by the UPMn0 bit. When enabled, the Parity
Checker calculates the parity of the data bits in incoming frames and compares the result withthe parity bit from the serial frame. The result of the check is stored in the receive buffer together
with the received data and stop bits. The Parity Error (UPEn) Flag can then be read by softwareto check if the frame had a Parity Error.

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The UPEn bit is set if the next character that can be read from the receive buffer had a Parity
Error when received and the Parity Checking was enabled at that point (UPMn1 = 1). This bit isvalid until the receive buffer (UDRn) is read.
17.6.6

Disabling the Receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing
receptions will therefore be lost. When disabled (i.e., the RXENn is set to zero) the Receiver will
no longer override the normal function of the RxDn port pin. The Receiver buffer FIFO will be
flushed when the Receiver is disabled. Remaining data in the buffer will be lost

17.6.7

Flushing the Receive Buffer
The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer will be
emptied of its contents. Unread data will be lost. If the buffer has to be flushed during normal
operation, due to for instance an error condition, read the UDRn I/O location until the RXCn Flag
is cleared. The following code example shows how to flush the receive buffer.
Assembly Code Example(1)USART_Flush:sbis UCSRnA, RXCn
retin

r16, UDRn

rjmp USART_FlushC Code Example(1)void USART_Flush( void ){unsigned char dummy;
while ( UCSRnA & (1<<RXCn) ) dummy = UDRn;
}
Note:

17.7

1. See “About Code Examples” on page 7.

Asynchronous Data Reception
The USART includes a clock recovery and a data recovery unit for handling asynchronous data
reception. The clock recovery logic is used for synchronizing the internally generated baud rate
clock to the incoming asynchronous serial frames at the RxDn pin. The data recovery logic samples and low pass filters each incoming bit, thereby improving the noise immunity of theReceiver. The asynchronous reception operational range depends on the accuracy of the internal baud rate clock, the rate of the incoming frames, and the frame size in number of bits.

17.7.1

Asynchronous Clock Recovery
The clock recovery logic synchronizes internal clock to the incoming serial frames. Figure 17-5
illustrates the sampling process of the start bit of an incoming frame. The sample rate is 16 times
the baud rate for Normal mode, and eight times the baud rate for Double Speed mode. The horizontal arrows illustrate the synchronization variation due to the sampling process. Note thelarger time variation when using the Double Speed mode (U2Xn = 1) of operation. Samples
denoted zero are samples done when the RxDn line is idle (i.e., no communication activity).

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Figure 17-5. Start Bit Sampling
RxD

IDLE

START

BIT 0

Sample(U2X = 0)

0

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

1

2

3

Sample(U2X = 1)

0

1

2

3

4

5

6

7

8

1

2

When the clock recovery logic detects a high (idle) to low (start) transition on the RxDn line, thestart bit detection sequence is initiated. Let sample 1 denote the first zero-sample as shown in
the figure. The clock recovery logic then uses samples 8, 9, and 10 for Normal mode, and samples 4, 5, and 6 for Double Speed mode (indicated with sample numbers inside boxes on the
figure), to decide if a valid start bit is received. If two or more of these three samples have logicalhigh levels (the majority wins), the start bit is rejected as a noise spike and the Receiver starts
looking for the next high to low-transition. If however, a valid start bit is detected, the clock recovery logic is synchronized and the data recovery can begin. The synchronization process isrepeated for each start bit.
17.7.2

Asynchronous Data Recovery
When the receiver clock is synchronized to the start bit, the data recovery can begin. The data
recovery unit uses a state machine that has 16 states for each bit in Normal mode and eightstates for each bit in Double Speed mode. Figure 17-6 shows the sampling of the data bits andthe parity bit. Each of the samples is given a number that is equal to the state of the recovery
unit.
Figure 17-6. Sampling of Data and Parity Bit
RxD

BIT n

Sample(U2X = 0)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

1

Sample(U2X = 1)

1

2

3

4

5

6

7

8

1

The decision of the logic level of the received bit is taken by doing a majority voting of the logic
value to the three samples in the center of the received bit. The center samples are emphasizedon the figure by having the sample number inside boxes. The majority voting process is done asfollows: If two or all three samples have high levels, the received bit is registered to be a logic 1.
If two or all three samples have low levels, the received bit is registered to be a logic 0. This
majority voting process acts as a low pass filter for the incoming signal on the RxDn pin. The
recovery process is then repeated until a complete frame is received. Including the first stop bit.
Note that the Receiver only uses the first stop bit of a frame.
Figure 17-7 shows the sampling of the stop bit and the earliest possible beginning of the start bitof the next frame.

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Figure 17-7. Stop Bit Sampling and Next Start Bit Sampling
RxD

STOP 1

(A)

(B)

(C)

Sample1(U2X = 0)

2

3

4

5

6

7

8

9

10

0/1

0/1

0/1

Sample1(U2X = 1)

2

3

4

5

6

0/1

The same majority voting is done to the stop bit as done for the other bits in the frame. If the stop
bit is registered to have a logic 0 value, the Frame Error (FEn) Flag will be set.
A new high to low transition indicating the start bit of a new frame can come right after the last of
the bits used for majority voting. For Normal Speed mode, the first low level sample can be atpoint marked (A) in Figure 17-7. For Double Speed mode the first low level must be delayed to(B). (C) marks a stop bit of full length. The early start bit detection influences the operational
range of the Receiver.
17.7.3Asynchronous Operational Range
The operational range of the Receiver is dependent on the mismatch between the received bit
rate and the internally generated baud rate. If the Transmitter is sending frames at too fast or too
slow bit rates, or the internally generated baud rate of the Receiver does not have a similar (seeTable 17-2) base frequency, the Receiver will not be able to synchronize the frames to the startbit.
The following equations can be used to calculate the ratio of the incoming data rate and internal
receiver baud rate.
( D + 1 )S
R slow = ------------------------------------------S – 1 + D ⋅ S + SF

( D + 2 )S
R fast = ----------------------------------( D + 1 )S + S M

DSum of character size and parity size (D = 5 to 10 bit)S

Samples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.

SF

First sample number used for majority voting. SF = 8 for normal speed and SF = 4
for Double Speed mode.

SM

Middle sample number used for majority voting. SM = 9 for normal speed andSM = 5 for Double Speed mode.

Rslow

is the ratio of the slowest incoming data rate that can be accepted in relation to thereceiver baud rate. Rfast is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.

Table 17-2 and Table 17-3 list the maximum receiver baud rate error that can be tolerated. Notethat Normal Speed mode has higher toleration of baud rate variations.

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Table 17-2.

Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2Xn = 0)D
# (Data+Parity Bit)

Rslow (%)

Rfast (%)

Max Total Error (%)

Recommended Max Receiver
Error (%)

5

93.20

106.67+6.67/-6.8

± 3.0

6

94.12

105.79+5.79/-5.88

± 2.5

7

94.81

105.11+5.11/-5.19

± 2.0

8

95.36

104.58+4.58/-4.54

± 2.0

9

95.81

104.14+4.14/-4.19

± 1.5

10

96.17

103.78+3.78/-3.83± 1.5

Table 17-3.

Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2Xn = 1)

D
# (Data+Parity Bit)

Rslow (%)

Rfast (%)

Max Total Error (%)

Recommended Max Receiver
Error (%)

5

94.12

105.66+5.66/-5.88

± 2.5

6

94.92

104.92+4.92/-5.08

± 2.0

7

95.52

104,35+4.35/-4.48

± 1.5

8

96.00

103.90+3.90/-4.00

± 1.5

9

96.39

103.53+3.53/-3.61

± 1.5

10

96.70

103.23+3.23/-3.30± 1.0

The recommendations of the maximum receiver baud rate error was made under the assumption that the Receiver and Transmitter equally divides the maximum total error.
There are two possible sources for the receivers baud rate error. The Receiver’s system clock(XTAL) will always have some minor instability over the supply voltage range and the temperature range. When using a crystal to generate the system clock, this is rarely a problem, but for aresonator the system clock may differ more than 2% depending of the resonators tolerance. The
second source for the error is more controllable. The baud rate generator can not always do anexact division of the system frequency to get the baud rate wanted. In this case an UBRR valuethat gives an acceptable low error can be used if possible.

17.8

Multi-processor Communication Mode
Setting the Multi-processor Communication mode (MPCMn) bit in UCSRnA enables a filteringfunction of incoming frames received by the USART Receiver. Frames that do not containaddress information will be ignored and not put into the receive buffer. This effectively reduces
the number of incoming frames that has to be handled by the CPU, in a system with multiple
MCUs that communicate via the same serial bus. The Transmitter is unaffected by the MPCMn
setting, but has to be used differently when it is a part of a system utilizing the Multi-processor
Communication mode.
If the Receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indicates if the frame contains data or address information. If the Receiver is set up for frames withnine data bits, then the ninth bit (RXB8n) is used for identifying address and data frames. Whenthe frame type bit (the first stop or the ninth bit) is one, the frame contains an address. When theframe type bit is zero the frame is a data frame.

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The Multi-processor Communication mode enables several slave MCUs to receive data from amaster MCU. This is done by first decoding an address frame to find out which MCU has beenaddressed. If a particular slave MCU has been addressed, it will receive the following data
frames as normal, while the other slave MCUs will ignore the received frames until anotheraddress frame is received.
17.8.1

Using MPCMn
For an MCU to act as a master MCU, it can use a 9-bit character frame format (UCSZn = 7). The
ninth bit (TXB8n) must be set when an address frame (TXB8n = 1) or cleared when a data frame(TXB = 0) is being transmitted. The slave MCUs must in this case be set to use a 9-bit character
frame format.
The following procedure should be used to exchange data in Multi-processor Communicationmode:
1. All Slave MCUs are in Multi-processor Communication mode (MPCMn in UCSRnA is
set).
2. The Master MCU sends an address frame, and all slaves receive and read this frame.
In the Slave MCUs, the RXCn Flag in UCSRnA will be set as normal.
3. Each Slave MCU reads the UDRn Register and determines if it has been selected. If
so, it clears the MPCMn bit in UCSRnA, otherwise it waits for the next address byte andkeeps the MPCMn setting.
4. The addressed MCU will receive all data frames until a new address frame is received.
The other Slave MCUs, which still have the MPCMn bit set, will ignore the data frames.
5. When the last data frame is received by the addressed MCU, the addressed MCU sets
the MPCMn bit and waits for a new address frame from master. The process thenrepeats from 2.
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the
Receiver must change between using n and n+1 character frame formats. This makes fullduplex operation difficult since the Transmitter and Receiver uses the same character size setting. If 5- to 8-bit character frames are used, the Transmitter must be set to use two stop bit(USBSn = 1) since the first stop bit is used for indicating the frame type.
Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCMn bit. The
MPCMn bit shares the same I/O location as the TXCn Flag and this might accidentally becleared when using SBI or CBI instructions.

17.9

Hardware Flow Control
The hardware flow control can be enabled by software.
CTS : (Clear to Send)
RTS : (Request to Send)
HOST

17.9.1

TXD

TXD

RXD

RXD

CTS

CTS

RTS

RTS

AT90USB82/162

Receiver Flow Control
The reception flow can be controlled by hardware using the RTS pin. The aim of the flow control
is to inform the external transmitter when the internal receive Fifo is full. Thus the transmitter can
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stop sending characters. RTS usage and so associated flow control is enabled using RTSEN bit
in UCSRnD.
Figure 17-8. shows a reception example.
Figure 17-8. Reception Flow Control Waveform Example
FIFO
Index

0

1

2 1

0

1

CPU Read
C1 C2

RXD

C3

RTS

Figure 17-9. RTS behavior
RXD

Start

Byte0

Stop

Start

Byte1

Stop

Start

Byte2

1 additional byte may be sent
if the transmitter misses the RTS trig

RTS
Read from CPU

RTS will rise at 2/3 of the last received stop bit if the receive fifo is full.
To ensure reliable transmissions, even after a RTS rise, an extra-data can still be received andstored in the Receive Shift Register.
17.9.2

Transmission Flow Control
The transmission flow can be controlled by hardware using the CTS pin controlled by the external receiver. The aim of the flow control is to stop transmission when the receiver is full of data
(CTS = 1). CTS usage and so associated flow control is enabled using CTSEN bit in UCSRnD.
The CTS pin is sampled at each CPU write and at the middle of the last stop bit that is
curently being sent.
Figure 17-10. CTS behavior
Write from CPU
TXD

Start
sample

Byte0

Stop

Start
sample

Byte1

Stop

Start

Byte2

sampleCTS

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17.10 USART Register Description
17.10.1

USART I/O Data Register n– UDRn
Bit

7

6

5

4

3

2

1

0

RXB[7:0]

UDRn (Read)

TXB[7:0]

UDRn (Write)

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers share thesame I/O address referred to as USART Data Register or UDRn. The Transmit Data Buffer Register (TXB) will be the destination for data written to the UDRn Register location. Reading the
UDRn Register location will return the contents of the Receive Data Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter and set tozero by the Receiver.
The transmit buffer can only be written when the UDREn Flag in the UCSRnA Register is set.
Data written to UDRn when the UDREn Flag is not set, will be ignored by the USART Transmitter. When data is written to the transmit buffer, and the Transmitter is enabled, the Transmitter
will load the data into the Transmit Shift Register when the Shift Register is empty. Then thedata will be serially transmitted on the TxDn pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever thereceive buffer is accessed. Due to this behavior of the receive buffer, do not use Read-ModifyWrite instructions (SBI and CBI) on this location. Be careful when using bit test instructions(SBIC and SBIS), since these also will change the state of the FIFO.
17.10.2

USART Control and Status Register A – UCSRnA
Bit

7

6

5

4

3

2

1

0

RXCn

TXCn

UDREn

FEn

DORn

UPEn

U2Xn

MPCMn

Read/Write

R

R/W

R

R

R

R

R/W

R/W

Initial Value

0

0

1

0

0

0

0

0

UCSRnA• Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive
buffer will be flushed and consequently the RXCn bit will become zero. The RXCn Flag can beused to generate a Receive Complete interrupt (see description of the RXCIEn bit).
• Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out andthere are no new data currently present in the transmit buffer (UDRn). The TXCn Flag bit is automatically cleared when a transmit complete interrupt is executed, or it can be cleared by writing
a one to its bit location. The TXCn Flag can generate a Transmit Complete interrupt (seedescription of the TXCIEn bit).
• Bit 5 – UDREn: USART Data Register Empty
The UDREn Flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREnis one, the buffer is empty, and therefore ready to be written. The UDREn Flag can generate a
Data Register Empty interrupt (see description of the UDRIEn bit).
UDREn is set after a reset to indicate that the Transmitter is ready.
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• Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when received. I.e.,
when the first stop bit of the next character in the receive buffer is zero. This bit is valid until thereceive buffer (UDRn) is read. The FEn bit is zero when the stop bit of received data is one.
Always set this bit to zero when writing to UCSRnA.
• Bit 3 – DORn: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occurs when the receive
buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a
new start bit is detected. This bit is valid until the receive buffer (UDRn) is read. Always set thisbit to zero when writing to UCSRnA.
• Bit 2 – UPEn: USART Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received and theParity Checking was enabled at that point (UPMn1 = 1). This bit is valid until the receive buffer(UDRn) is read. Always set this bit to zero when writing to UCSRnA.
• Bit 1 – U2Xn: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer rate for asynchronous communication.
• Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCMn bit is written toone, all the incoming frames received by the USART Receiver that do not contain address information will be ignored. The Transmitter is unaffected by the MPCMn setting. For more detailed
information see “Multi-processor Communication Mode” on page 162.
17.10.3

USART Control and Status Register n B – UCSRnB
Bit

7

6

5

4

3

2

1

0

RXCIEnTXCIEnUDRIEn

RXENn

TXENn

UCSZn2

RXB8n

TXB8n

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R

R/W

Initial Value

0

0

0

0

0

0

0

0

UCSRnB• Bit 7 – RXCIEn: RX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete interrupt
will be generated only if the RXCIEn bit is written to one, the Global Interrupt Flag in SREG iswritten to one and the RXCn bit in UCSRnA is set.
• Bit 6 – TXCIEn: TX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the TXCn Flag. A USART Transmit Complete interrupt
will be generated only if the TXCIEn bit is written to one, the Global Interrupt Flag in SREG iswritten to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable n
Writing this bit to one enables interrupt on the UDREn Flag. A Data Register Empty interrupt will
be generated only if the UDRIEn bit is written to one, the Global Interrupt Flag in SREG is written
to one and the UDREn bit in UCSRnA is set.

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AT90USB82/162• Bit 4 – RXENn: Receiver Enable n
Writing this bit to one enables the USART Receiver. The Receiver will override normal port operation for the RxDn pin when enabled. Disabling the Receiver will flush the receive buffer
invalidating the FEn, DORn, and UPEn Flags.
• Bit 3 – TXENn: Transmitter Enable n
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port
operation for the TxDn pin when enabled. The disabling of the Transmitter (writing TXENn tozero) will not become effective until ongoing and pending transmissions are completed, i.e.,
when the Transmit Shift Register and Transmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter will no longer override the TxDn port.
• Bit 2 – UCSZn2: Character Size n
The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8n: Receive Data Bit 8 n
RXB8n is the ninth data bit of the received character when operating with serial frames with nine
data bits. Must be read before reading the low bits from UDRn.
• Bit 0 – TXB8n: Transmit Data Bit 8 n
TXB8n is the ninth data bit in the character to be transmitted when operating with serial frameswith nine data bits. Must be written before writing the low bits to UDRn.
17.10.4

USART Control and Status Register n C – UCSRnC
Bit

7

6

5

4

3

2

1

0

UMSELn1

UMSELn0

UPMn1

UPMn0

USBSn

UCSZn1UCSZn0UCPOLnRead/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

1

1

0

UCSRnC• Bits 7:6 – UMSELn1:0 USART Mode Select
These bits select the mode of operation of the USARTn as shown in Table 17-4..
Table 17-4.

UMSELn Bits Settings

UMSELn1

UMSELn000Asynchronous USART

0

1

Synchronous USART

1

0(Reserved)

1

1

Master SPI (MSPIM)(1)

Note:

Mode

1. See “USART in SPI Mode” on page 173 for full description of the Master SPI Mode (MSPIM)
operation• Bits 5:4 – UPMn1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the Transmitter willautomatically generate and send the parity of the transmitted data bits within each frame. The

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Receiver will generate a parity value for the incoming data and compare it to the UPMn setting.
If a mismatch is detected, the UPEn Flag in UCSRnA will be set.
Table 17-5.

UPMn Bits Settings

UPMn1

UPMn0

Parity Mode00

Disabled

01

Reserved

10Enabled, Even Parity

1

1

Enabled, Odd Parity• Bit 3 – USBSn: Stop Bit SelectThis bit selects the number of stop bits to be inserted by the Transmitter. The Receiver ignores
this setting.
Table 17-6.

USBS Bit Settings
USBSn

Stop Bit(s)

0

1-bit

1

2-bit

• Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use.
Table 17-7.

UCSZn Bits Settings

UCSZn2

UCSZn1UCSZn0Character Size

0

0

0

5-bit

0

0

1

6-bit

0

1

0

7-bit

0

1

1

8-bit

1

0

0

Reserved

10

1Reserved1

10

Reserved

1

1

1

9-bit

• Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode isused. The UCPOLn bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCKn).
Table 17-8.
UCPOLn168

UCPOLn Bit Settings
Transmitted Data Changed (Output of TxDn Pin)

Received Data Sampled (Input on RxDn Pin)0

Rising XCKn Edge

Falling XCKn Edge

1

Falling XCKn Edge

Rising XCKn Edge

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AT90USB82/162
17.10.5

USART Control and Status Register n D – UCSRnD
Bit

7

6

5

4

3

2

1

0

-

-

-

-

-

-

CTSEN

RTSEN

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

UCSRnD• Bits 1 – CTSEN : USART CTS Enable
Set this bit to one by firmware to enable the transmission flow control (CTS). Transmission isallowed if CTS = 0.
Set this bit to zero by firmware to disable the transmission flow control (CTS). Transmission isalways allowed.
• Bits 0 – RTSEN : USART RTS Enable
Set this bit to one by firmware to enable the receive flow control (RTS).
Set this bit to zero by firmware to disable the receive flow control (RTS).
17.10.6

USART Baud Rate Registers – UBRRLn and UBRRHn
Bit

15

14

13

12

11

–

–

–

–

UBRR[11:8]

10

9

8

7

6

5

4

3

R

R

R

R

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

UBRRHnUBRR[7:0]
Read/Write
Initial ValueUBRRLn2

10• Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be
written to zero when UBRRH is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the fourmost significant bits, and the UBRRL contains the eight least significant bits of the USART baudrate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud rate ischanged. Writing UBRRL will trigger an immediate update of the baud rate prescaler.

17.11 Examples of Baud Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asynchronous operation can be generated by using the UBRR settings in Table 17-9 to Table 17-12.
UBRR values which yield an actual baud rate differing less than 0.5% from the target baud rate,
are bold in the table. Higher error ratings are acceptable, but the Receiver will have less noise
resistance when the error ratings are high, especially for large serial frames (see “Asynchronous
Operational Range” on page 161). The error values are calculated using the following equation:
BaudRate Closest Match
Error[%] = ⎛ -------------------------------------------------------- – 1⎞ • 100%⎝⎠
BaudRate

169
7707E–AVR–11/08

Table 17-9.

Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
fosc = 1.0000 MHz

fosc = 1.8432 MHz

fosc = 2.0000 MHz

Baud
Rate
(bps)

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

2400

25

0.2%

51

0.2%

47

0.0%

95

0.0%

51

0.2%

103

0.2%

4800

12

0.2%

25

0.2%

23

0.0%

47

0.0%

25

0.2%

51

0.2%

9600

6

-7.0%

12

0.2%

11

0.0%

23

0.0%

12

0.2%

25

0.2%

14.4k

3

8.5%

8

-3.5%

7

0.0%

15

0.0%

8

-3.5%

16

2.1%

19.2k

2

8.5%

6

-7.0%

5

0.0%

11

0.0%

6

-7.0%

12

0.2%

28.8k

1

8.5%

3

8.5%

3

0.0%

7

0.0%

3

8.5%

8

-3.5%

38.4k

1

-18.6%

2

8.5%

2

0.0%

5

0.0%

2

8.5%

6

-7.0%

57.6k

0

8.5%

1

8.5%

1

0.0%

3

0.0%

1

8.5%

3

8.5%

76.8k

–

–

1

-18.6%

1-25.0%

20.0%

1-18.6%

2

8.5%

115.2k

–

–

0

8.5%

0

0.0%

1

0.0%

0

8.5%

1

8.5%

230.4k

–

–

–

–

–

–

0

0.0%

–

–

–

–

250k

–

–

–

–

–

–

–

–

–

–

0

0.0%

Max. (1)62.5 kbps

1.

170

U2Xn = 0

U2Xn = 1

125 kbps

U2Xn = 0

115.2 kbps

U2Xn = 1

230.4 kbps

U2Xn = 0

125 kbps

U2Xn = 1

250 kbps

UBRR = 0, Error = 0.0%

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AT90USB82/162
Table 17-10. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
Baud
Rate
(bps)

fosc = 3.6864 MHz
U2Xn = 0

fosc = 4.0000 MHz
U2Xn = 1

U2Xn = 0

fosc = 7.3728 MHz
U2Xn = 1

U2Xn = 0

U2Xn = 1

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

2400

95

0.0%

191

0.0%

103

0.2%

207

0.2%

191

0.0%

383

0.0%

4800

47

0.0%

95

0.0%

51

0.2%

103

0.2%

95

0.0%

191

0.0%

9600

23

0.0%

47

0.0%

25

0.2%

51

0.2%

47

0.0%

95

0.0%

14.4k

15

0.0%

31

0.0%

16

2.1%

34

-0.8%

31

0.0%

63

0.0%

19.2k

11

0.0%

23

0.0%

12

0.2%

25

0.2%

23

0.0%

47

0.0%

28.8k

7

0.0%

15

0.0%

8

-3.5%

16

2.1%

15

0.0%

31

0.0%

38.4k

5

0.0%

11

0.0%

6

-7.0%

12

0.2%

11

0.0%

23

0.0%

57.6k

3

0.0%

7

0.0%

3

8.5%

8

-3.5%

7

0.0%

15

0.0%

76.8k

2

0.0%

5

0.0%

2

8.5%

6

-7.0%

5

0.0%

11

0.0%

115.2k

1

0.0%

3

0.0%

1

8.5%

3

8.5%

3

0.0%

7

0.0%

230.4k

0

0.0%

1

0.0%

0

8.5%

1

8.5%

1

0.0%

3

0.0%

250k

0

-7.8%

1

-7.8%

0

0.0%

1

0.0%

1

-7.8%

3

-7.8%

0.5M

–

–

0

-7.8%

–

–

0

0.0%

0

-7.8%

1

-7.8%

–

–

–

–

–

–

–

–

–

–

0

-7.8%

1M
Max.
1.

(1)

230.4 kbps

460.8 kbps

250 kbps

0.5 Mbps

460.8 kbps

921.6 kbps

UBRR = 0, Error = 0.0%

1717707E–AVR–11/08

Table 17-11. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 11.0592 MHz

fosc = 8.0000 MHz

fosc = 14.7456 MHz

Baud
Rate
(bps)

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

2400

207

0.2%

416

-0.1%

287

0.0%

575

0.0%

383

0.0%

767

0.0%

4800

103

0.2%

207

0.2%

143

0.0%

287

0.0%

191

0.0%

383

0.0%

9600

51

0.2%

103

0.2%

71

0.0%

143

0.0%

95

0.0%

191

0.0%

14.4k

34

-0.8%

68

0.6%

47

0.0%

95

0.0%

63

0.0%

127

0.0%

19.2k

25

0.2%

51

0.2%

35

0.0%

71

0.0%

47

0.0%

95

0.0%

28.8k

16

2.1%

34

-0.8%

23

0.0%

47

0.0%

31

0.0%

63

0.0%

38.4k

12

0.2%

25

0.2%

17

0.0%

35

0.0%

23

0.0%

47

0.0%

57.6k

8

-3.5%

16

2.1%

11

0.0%

23

0.0%

15

0.0%

31

0.0%

76.8k

6

-7.0%

12

0.2%

8

0.0%

17

0.0%

11

0.0%

23

0.0%

115.2k

3

8.5%

8

-3.5%

5

0.0%

11

0.0%

7

0.0%

15

0.0%

230.4k

1

8.5%

3

8.5%

2

0.0%

5

0.0%

3

0.0%

7

0.0%

250k

1

0.0%

3

0.0%

2

-7.8%

5

-7.8%

3

-7.8%

6

5.3%

0.5M

0

0.0%

1

0.0%

–

–

2

-7.8%

1

-7.8%

3

-7.8%

–

–

0

0.0%

–

–

–

–

0

-7.8%

1

-7.8%

1M
Max.
1.

172

(1)

U2Xn = 0

U2Xn = 1

0.5 Mbps

1 MbpsU2Xn = 0691.2 kbps

U2Xn = 1

1.3824 Mbps

U2Xn = 0921.6 kbps

U2Xn = 1

1.8432 MbpsUBRR = 0, Error = 0.0%

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AT90USB82/162
Table 17-12. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies (Continued)
fosc = 16.0000 MHz

fosc = 18.4320 MHz

fosc = 20.0000 MHz

Baud
Rate
(bps)

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

UBRR

Error

2400

416

-0.1%

832

0.0%

479

0.0%

959

0.0%

520

0.0%

1041

0.0%

4800

207

0.2%

416

-0.1%

239

0.0%

479

0.0%

259

0.2%

520

0.0%

9600

103

0.2%

207

0.2%

119

0.0%

239

0.0%

129

0.2%

259

0.2%

14.4k

68

0.6%

138

-0.1%

79

0.0%

159

0.0%

86

-0.2%

173

-0.2%

19.2k

51

0.2%

103

0.2%

59

0.0%

119

0.0%

64

0.2%

129

0.2%

28.8k

34

-0.8%

68

0.6%

39

0.0%

79

0.0%

42

0.9%

86

-0.2%

38.4k

25

0.2%

51

0.2%

29

0.0%

59

0.0%

32

-1.4%

64

0.2%

57.6k

16

2.1%

34

-0.8%

19

0.0%

39

0.0%

21

-1.4%

42

0.9%

76.8k

12

0.2%

25

0.2%

14

0.0%

29

0.0%

15

1.7%

32

-1.4%

115.2k

8

-3.5%

16

2.1%

9

0.0%

19

0.0%

10

-1.4%

21

-1.4%

230.4k

3

8.5%

8

-3.5%

4

0.0%

9

0.0%

4

8.5%

10

-1.4%

250k

3

0.0%

7

0.0%

4

-7.8%

8

2.4%

4

0.0%

9

0.0%

0.5M

1

0.0%

3

0.0%

–

–

4

-7.8%

–

–

4

0.0%

0

0.0%

1

0.0%

–

–

–

–

–

–

–

–

1M
Max.
1.

U2Xn = 0(1)

U2Xn = 1

1 Mbps

2 MbpsU2Xn = 0

1.152 Mbps

U2Xn = 1

U2Xn = 02.304 Mbps

1.25 Mbps

U2Xn = 1

2.5 Mbps

UBRR = 0, Error = 0.0%

18. USART in SPI Mode
The Universal Synchronous and Asynchronous serial Receiver and Transmitter (USART) can be
set to a master SPI compliant mode of operation. The Master SPI Mode (MSPIM) has the following features:• Full Duplex, Three-wire Synchronous Data Transfer• Master Operation• Supports all four SPI Modes of Operation (Mode 0, 1, 2, and 3)• LSB First or MSB First Data Transfer (Configurable Data Order)• Queued Operation (Double Buffered)• High Resolution Baud Rate Generator• High Speed Operation (fXCKmax = fCK/2)• Flexible Interrupt Generation

18.1

Overview
Setting both UMSELn1:0 bits to one enables the USART in MSPIM logic. In this mode of operation the SPI master control logic takes direct control over the USART resources. These
resources include the transmitter and receiver shift register and buffers, and the baud rate generator. The parity generator and checker, the data and clock recovery logic, and the RX and TX
173

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control logic is disabled. The USART RX and TX control logic is replaced by a common SPI
transfer control logic. However, the pin control logic and interrupt generation logic is identical inboth modes of operation.
The I/O register locations are the same in both modes. However, some of the functionality of thecontrol registers changes when using MSPIM.

18.2

Clock Generation
The Clock Generation logic generates the base clock for the Transmitter and Receiver. For
USART MSPIM mode of operation only internal clock generation (i.e. master operation) is supported. The Data Direction Register for the XCKn pin (DDR_XCKn) must therefore be set to one(i.e. as output) for the USART in MSPIM to operate correctly. Preferably the DDR_XCKn should
be set up before the USART in MSPIM is enabled (i.e. TXENn and RXENn bit set to one).
The internal clock generation used in MSPIM mode is identical to the USART synchronous master mode. The baud rate or UBRRn setting can therefore be calculated using the same
equations, see Table 18-1:

Table 18-1.

Equations for Calculating Baud Rate Register Setting

Operating Mode

Equation for Calculating Baud Rate(1)Equation for Calculating UBRRn Valuef OSC
BAUD = --------------------------------------2 ( UBRRn + 1 )f OSC
UBRRn = -------------------- – 1
2BAUD

Synchronous Master mode

Note:

174

1. The baud rate is defined to be the transfer rate in bit per second (bps)

BAUD

Baud rate (in bits per second, bps)

fOSC

System Oscillator clock frequency

UBRRn

Contents of the UBRRnH and UBRRnL Registers, (0-4095)

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AT90USB82/162
18.3

SPI Data Modes and Timing
There are four combinations of XCKn (SCK) phase and polarity with respect to serial data, which
are determined by control bits UCPHAn and UCPOLn. The data transfer timing diagrams areshown in Figure 18-1. Data bits are shifted out and latched in on opposite edges of the XCKn
signal, ensuring sufficient time for data signals to stabilize. The UCPOLn and UCPHAn functionality is summarized in Table 18-2. Note that changing the setting of any of these bits will corrupt
all ongoing communication for both the Receiver and Transmitter.

Table 18-2.

UCPOLn and UCPHAn Functionality-

UCPOLnUCPHAn

SPI Mode

Leading Edge

Trailing Edge

0

0

0

Sample (Rising)

Setup (Falling)

0

1

1

Setup (Rising)

Sample (Falling)

1

0

2

Sample (Falling)

Setup (Rising)

1

1

3

Setup (Falling)

Sample (Rising)

Figure 18-1. UCPHAn and UCPOLn data transfer timing diagrams.

UCPHA=0

UCPHA=1

UCPOL=018.4

UCPOL=1

XCK

XCK

Data setup (TXD)

Data setup (TXD)

Data sample (RXD)

Data sample (RXD)

XCK

XCK

Data setup (TXD)

Data setup (TXD)

Data sample (RXD)

Data sample (RXD)

Frame Formats
A serial frame for the MSPIM is defined to be one character of 8 data bits. The USART in MSPIM
mode has two valid frame formats:• 8-bit data with MSB first• 8-bit data with LSB firstA frame starts with the least or most significant data bit. Then the next data bits, up to a total ofeight, are succeeding, ending with the most or least significant bit accordingly. When a complete
frame is transmitted, a new frame can directly follow it, or the communication line can be set toan idle (high) state.
The UDORDn bit in UCSRnC sets the frame format used by the USART in MSPIM mode. The
Receiver and Transmitter use the same setting. Note that changing the setting of any of thesebits will corrupt all ongoing communication for both the Receiver and Transmitter.
16-bit data transfer can be achieved by writing two data bytes to UDRn. A UART transmit complete interrupt will then signal that the 16-bit value has been shifted out.

175
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18.4.1

USART MSPIM Initialization
The USART in MSPIM mode has to be initialized before any communication can take place. The
initialization process normally consists of setting the baud rate, setting master mode of operation(by setting DDR_XCKn to one), setting frame format and enabling the Transmitter and theReceiver. Only the transmitter can operate independently. For interrupt driven USART operation, the Global Interrupt Flag should be cleared (and thus interrupts globally disabled) when
doing the initialization.
Note:

To ensure immediate initialization of the XCKn output the baud-rate register (UBRRn) must be
zero at the time the transmitter is enabled. Contrary to the normal mode USART operation the
UBRRn must then be written to the desired value after the transmitter is enabled, but before thefirst transmission is started. Setting UBRRn to zero before enabling the transmitter is not necessary if the initialization is done immediately after a reset since UBRRn is reset to zero.

Before doing a re-initialization with changed baud rate, data mode, or frame format, be sure that
there is no ongoing transmissions during the period the registers are changed. The TXCn Flag
can be used to check that the Transmitter has completed all transfers, and the RXCn Flag canbe used to check that there are no unread data in the receive buffer. Note that the TXCn Flag
must be cleared before each transmission (before UDRn is written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C function that are equal in functionality. The examples assume polling (no interrupts enabled). The
baud rate is given as a function parameter. For the assembly code, the baud rate parameter isassumed to be stored in the r17:r16 registers.

176

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AT90USB82/162
Assembly Code Example(1)USART_Init:clr r18
out UBRRnH,r18
out UBRRnL,r18; Setting the XCKn port pin as output, enables master mode.
sbi XCKn_DDR, XCKn
; Set MSPI mode of operation and SPI data mode 0.
ldi r18, (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn)
out UCSRnC,r18; Enable receiver and transmitter.
ldi r18, (1<<RXENn)|(1<<TXENn)
out UCSRnB,r18; Set baud rate.
; IMPORTANT: The Baud Rate must be set after the transmitter is enabled!
out UBRRnH, r17
out UBRRnL, r18
ret

C Code Example(1)void USART_Init( unsigned int baud ){UBRRn = 0;/* Setting the XCKn port pin as output, enables master mode. */XCKn_DDR |= (1<<XCKn);/* Set MSPI mode of operation and SPI data mode 0. */UCSRnC = (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn);/* Enable receiver and transmitter. */UCSRnB = (1<<RXENn)|(1<<TXENn);/* Set baud rate. *//* IMPORTANT: The Baud Rate must be set after the transmitter is enabled*/
UBRRn = baud;
}
Note:

18.5

1. See “About Code Examples” on page 7.

Data Transfer
Using the USART in MSPI mode requires the Transmitter to be enabled, i.e. the TXENn bit in
the UCSRnB register is set to one. When the Transmitter is enabled, the normal port operationof the TxDn pin is overridden and given the function as the Transmitter's serial output. Enabling
the receiver is optional and is done by setting the RXENn bit in the UCSRnB register to one.
When the receiver is enabled, the normal pin operation of the RxDn pin is overridden and given
the function as the Receiver's serial input. The XCKn will in both cases be used as the transfer
clock.
After initialization the USART is ready for doing data transfers. A data transfer is initiated by writing to the UDRn I/O location. This is the case for both sending and receiving data since the177

7707E–AVR–11/08

transmitter controls the transfer clock. The data written to UDRn is moved from the transmit buffer to the shift register when the shift register is ready to send a new frame.
Note:

To keep the input buffer in sync with the number of data bytes transmitted, the UDRn register must
be read once for each byte transmitted. The input buffer operation is identical to normal USART
mode, i.e. if an overflow occurs the character last received will be lost, not the first data in the buffer. This means that if four bytes are transferred, byte 1 first, then byte 2, 3, and 4, and the UDRn
is not read before all transfers are completed, then byte 3 to be received will be lost, and not byte
1.

The following code examples show a simple USART in MSPIM mode transfer function based onpolling of the Data Register Empty (UDREn) Flag and the Receive Complete (RXCn) Flag. The
USART has to be initialized before the function can be used. For the assembly code, the data to
be sent is assumed to be stored in Register R16 and the data received will be available in thesame register (R16) after the function returns.
The function simply waits for the transmit buffer to be empty by checking the UDREn Flag,
before loading it with new data to be transmitted. The function then waits for data to be present
in the receive buffer by checking the RXCn Flag, before reading the buffer and returning thevalue..
Assembly Code Example(1)USART_MSPIM_Transfer:; Wait for empty transmit buffer
sbis UCSRnA, UDREn
rjmp USART_MSPIM_Transfer; Put data (r16) into buffer, sends the dataout UDRn,r16; Wait for data to be received
USART_MSPIM_Wait_RXCn:sbis UCSRnA, RXCn
rjmp USART_MSPIM_Wait_RXCn; Get and return received data from bufferin r16, UDRnret

C Code Example(1)unsigned char USART_Receive( void ){/* Wait for empty transmit buffer */while ( !( UCSRnA & (1<<UDREn)) );/* Put data into buffer, sends the data */UDRn = data;/* Wait for data to be received */while ( !(UCSRnA & (1<<RXCn)) );/* Get and return received data from buffer */return UDRn;
}
Note:

178

1. See “About Code Examples” on page 7.

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18.5.1

Transmitter and Receiver Flags and Interrupts
The RXCn, TXCn, and UDREn flags and corresponding interrupts in USART in MSPIM mode
are identical in function to the normal USART operation. However, the receiver error status flags(FE, DOR, and PE) are not in use and is always read as zero.

18.5.2Disabling the Transmitter or Receiver
The disabling of the transmitter or receiver in USART in MSPIM mode is identical in function to
the normal USART operation.

18.6

USART MSPIM Register Description
The following section describes the registers used for SPI operation using the USART.

18.6.1

USART MSPIM I/O Data Register - UDRn
The function and bit description of the USART data register (UDRn) in MSPI mode is identical tonormal USART operation. See “USART I/O Data Register n– UDRn” on page 165.

18.6.2

USART MSPIM Control and Status Register n A - UCSRnA
•
Bit

7

6

5

4

3

2

1

0

RXCn

TXCn

UDREn

-

-

-

-

-

Read/Write

R/W

R/W

R/W

R

R

R

R

R

Initial Value

0

0

0

0

0

1

1

0

UCSRnA• Bit 7 - RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive
buffer will be flushed and consequently the RXCn bit will become zero. The RXCn Flag can beused to generate a Receive Complete interrupt (see description of the RXCIEn bit).
• Bit 6 - TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out andthere are no new data currently present in the transmit buffer (UDRn). The TXCn Flag bit is automatically cleared when a transmit complete interrupt is executed, or it can be cleared by writing
a one to its bit location. The TXCn Flag can generate a Transmit Complete interrupt (seedescription of the TXCIEn bit).
• Bit 5 - UDREn: USART Data Register Empty
The UDREn Flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREnis one, the buffer is empty, and therefore ready to be written. The UDREn Flag can generate a
Data Register Empty interrupt (see description of the UDRIE bit). UDREn is set after a reset toindicate that the Transmitter is ready.
• Bit 4:0 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices,
these bits must be written to zero when UCSRnA is written.

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18.6.3

USART MSPIM Control and Status Register n B - UCSRnB
Bit

7

6

5

4

3

2

1

RXCIEnTXCIEn

UDRIE

RXENn

TXENn

-

-

0
-

Read/Write

R/W

R/W

R/W

R/W

R/W

R

R

R

Initial Value

0

0

0

0

0

1

1

0

UCSRnB• Bit 7 - RXCIEn: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete interrupt
will be generated only if the RXCIEn bit is written to one, the Global Interrupt Flag in SREG iswritten to one and the RXCn bit in UCSRnA is set.
• Bit 6 - TXCIEn: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXCn Flag. A USART Transmit Complete interrupt
will be generated only if the TXCIEn bit is written to one, the Global Interrupt Flag in SREG iswritten to one and the TXCn bit in UCSRnA is set.
• Bit 5 - UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDREn Flag. A Data Register Empty interrupt will
be generated only if the UDRIE bit is written to one, the Global Interrupt Flag in SREG is written
to one and the UDREn bit in UCSRnA is set.
• Bit 4 - RXENn: Receiver Enable
Writing this bit to one enables the USART Receiver in MSPIM mode. The Receiver will override
normal port operation for the RxDn pin when enabled. Disabling the Receiver will flush thereceive buffer. Only enabling the receiver in MSPI mode (i.e. setting RXENn=1 and TXENn=0)
has no meaning since it is the transmitter that controls the transfer clock and since only mastermode is supported.
• Bit 3 - TXENn: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port
operation for the TxDn pin when enabled. The disabling of the Transmitter (writing TXENn tozero) will not become effective until ongoing and pending transmissions are completed, i.e.,
when the Transmit Shift Register and Transmit Buffer Register do not contain data to be transmitted. When disabled, the Transmitter will no longer override the TxDn port.
• Bit 2:0 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices,
these bits must be written to zero when UCSRnB is written.

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18.6.4

USART MSPIM Control and Status Register n C - UCSRnC
Bit

7

6

5

4

3

2

1

UMSELn1

UMSELn0---

UDORDnUCPHAn0
UCPOLnRead/Write

R/W

R/W

R

R

R

R/W

R/W

R/W

Initial Value

0

0

0

0

0

1

1

0

UCSRnC• Bit 7:6 - UMSELn1:0: USART Mode Select
These bits select the mode of operation of the USART as shown in Table 18-3. See “USART
Control and Status Register n C – UCSRnC” on page 167 for full description of the normal
USART operation. The MSPIM is enabled when both UMSELn bits are set to one. The
UDORDn, UCPHAn, and UCPOLn can be set in the same write operation where the MSPIM isenabled.
Table 18-3.

UMSELn Bits Settings

UMSELn1

UMSELn0

Mode

0

0

Asynchronous USART

0

1

Synchronous USART

1

0(Reserved)

1

1

Master SPI (MSPIM)• Bit 5:3 - Reserved Bits in MSPI mode
When in MSPI mode, these bits are reserved for future use. For compatibility with future devices,
these bits must be written to zero when UCSRnC is written.
• Bit 2 - UDORDn: Data Order
When set to one the LSB of the data word is transmitted first. When set to zero the MSB of thedata word is transmitted first. Refer to the Frame Formats section page 4 for details.
• Bit 1 - UCPHAn: Clock Phase
The UCPHAn bit setting determine if data is sampled on the leasing edge (first) or tailing (last)edge of XCKn. Refer to the SPI Data Modes and Timing section page 4 for details.
• Bit 0 - UCPOLn: Clock Polarity
The UCPOLn bit sets the polarity of the XCKn clock. The combination of the UCPOLn and
UCPHAn bit settings determine the timing of the data transfer. Refer to the SPI Data Modes andTiming section page 4 for details.
18.6.5

18.7

USART MSPIM Baud Rate Registers - UBRRnL and UBRRnH
The function and bit description of the baud rate registers in MSPI mode is identical to normal
USART operation. See “USART Baud Rate Registers – UBRRLn and UBRRHn” on page 169.

AVR USART MSPIM vs.
AVR SPIThe USART in MSPIM mode is fully compatible with the AVR SPI regarding:• Master mode timing diagram.
• The UCPOLn bit functionality is identical to the SPI CPOL bit.
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• The UCPHAn bit functionality is identical to the SPI CPHA bit.
• The UDORDn bit functionality is identical to the SPI DORD bit.
However, since the USART in MSPIM mode reuses the USART resources, the use of the
USART in MSPIM mode is somewhat different compared to the SPI. In addition to differences of
the control register bits, and that only master operation is supported by the USART in MSPIM
mode, the following features differ between the two modules:• The USART in MSPIM mode includes (double) buffering of the transmitter. The SPI has nobuffer.
• The USART in MSPIM mode receiver includes an additional buffer level.
• The SPI WCOL (Write Collision) bit is not included in USART in MSPIM mode.
• The SPI double speed mode (SPI2X) bit is not included. However, the same effect isachieved by setting UBRRn accordingly.
• Interrupt timing is not compatible.
• Pin control differs due to the master only operation of the USART in MSPIM mode.
A comparison of the USART in MSPIM mode and the SPI pins is shown in Table 18-4 on page
182.

Table 18-4.

182

Comparison of USART in MSPIM mode and SPI pins.

USART_MSPIM

SPIComment

TxDn

MOSI

Master Out only

RxDn

MISO

Master In only

XCKn

SCK

(Functionally identical)

(N/A)

SS

Not supported by USART in MSPIM

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19. USB controller
19.1

Features• Support full-speed• Support ping-pong mode (dual bank), with transparent switch• 176 bytes of DPRAM– 1 endpoint of 64 bytes max, (default control endpoint)– 2 endpoints of 64 bytes max, (one bank)– 2 endpoints of 64 bytes max, (one or two banks)

19.2

Block Diagram
The USB controller provides the hardware to interface a USB link to a data flow stored in a double port memory (DPRAM).
The USB controller requires a 48 MHz ±0.25% reference clock (for Full-speed compliance),
which is the output of an internal PLL. The PLL generates the internal high frequency (48 MHz)
clock for USB interface, the PLL input is generated from an external lower frequency (the crystal
oscillator or external clock input pin from XTAL1, to satisfy the USB frequency accuracy and jitter; only this clock source allows proper functionnality of the USB controller).
The 48MHz clock is used to generate a 12 MHz Full-speed bit clock from the received USB differential data and to transmit data according to full speed USB device tolerance. Clock recovery
is done by a Digital Phase Locked Loop (DPLL) block, which is compliant with the jitter specification of the USB bus.
To comply the USB Electrical characteristics, USB Pads (D+ or D-) should be powered within
the 3.0 to 3.6V range. As AT90USB82/162 can be powered up to 5.5V, the internal regulator
provides the USB pads power supply.

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Figure 19-1. USB controller Block Diagram overview
UVCC

XTAL1

Regulator

PLL
6x

UCAP

clk
8MHz

PLL clock
Prescaler

clk
48MHz

CPU

D-

DPLL
Clock
RecoveryD+

USB
Interface

On-Chip
USB DPRAM

19.3

Typical Application Implementation
Depending on the target application power supply, the AT90USB82/162 requires different hardware typical implementations.
Figure 19-2. Operating modes versus frequency and power-supply
Max
Operating Frequency (MHz)VCC (V)

5.5
16 MHz4.5

USB compliant,with internal regulator

4.0
3.6
8 MHz
USB compliant,without internal regulator
3.0
2.7
VCC minUSB not operational

2 MHz

0

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19.3.1Bus Powered device
Figure 19-3. Typical Bus powered application with 5V I/O

VCC

UCAP

1µF

VBUS

UVCC

UDP

D+

UDM

D-

UVSS

UVSS

VSS

XTAL1

XTAL2

Figure 19-4. Typical Bus powered application with 3V I/O

VCC

UCAP
1µF

VBUS

UVCC

UDM

D+

UDP

D-

UVSS

UVSS

VSS

XTAL1

XTAL2

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19.3.2

Self Powered device
Figure 19-5. Typical Self powered application with 3.4V to 5.5V I/O
External 3.4V - 5.5V
Power Supply

UVCC

AVCC

VCC

UCAP

1µF

UDP

D+
Rs=22

UDM

DRs=22

UVSS

UGND

XTAL1

XTAL2

GND

GND

Typical Self powered application with 3.0V to 3.6 I/OExternal 3.0V - 3.6V
Power Supply

UVCC

AVCC

VCC

UCAP

1µF

UDP

D+
Rs=22

UDM

DRs=22

UVSS

UGND

XTAL1

186

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XTAL2

GND

GND

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19.3.3

Design guidelines• Serial resistors on USB Data lines must have 22 Ohms value (+/- 5%).
• Traces from the input USB receptable (or from the cable connection in the case of a tethereddevice) to the USB microcontroller pads should be as short as possibles, and follow
differential traces routing rules (same length, as near as possible, avoid vias accumulation).
• Voltage transcient / ESD suppressors may also be used to prevent USB pads to be damagedby external disturbances.
• Ucap capacitor should be 1µF (+/- 10%) for correct operation.
• A 10µF capacitor is highly recommended on VBUS line

19.4
19.4.1

General Operating Modes
Introduction
The USB controller is disabled and reset after a hardware reset generated by:– Power on reset– External reset– Watchdog reset– Brown out reset– debugWIRE reset
But another available and optionnal reset source is :– USB End Of Reset
In this case, the USB controller is reset, but not disabled (so that the device remains attached).

19.4.2

Power-on and reset
The next diagram explains the USB controller main states on power-on:
Figure 19-6. USB controller states after reset
Clockstopped
FRZCLK=1
Macrooff

USBE=0Reset

USBE=1<any otherstate>HW RESET(exceptedfromEOR)
USBE=0

USBE=0Dev ice
HW RESET from EOR

When the USB controller is in reset state:• USBE is not set

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• the USB controller clock is stopped in order to minimize the power consumption(FRZCLK=1),• the USB controller is disabled,• USB is in the suspend mode,• the Device USB controllers internal state is reset.
• The DPACC bit and the DPADD10:0 field can be set by software. The DPRAM is not cleared.
• The SPDCONF bits can be set by software.
After setting USBE, the USB Controller enters in the Device state.
The USB Controller can at any time be ‘stopped’ by clearing USBE. In fact, clearing USBE acts
as an hardware reset on the USB macro.
19.4.3

Interrupts
Two interrupts vectors are assigned to USB controller.
Figure 19-7. USB Interrupt System
USB Device
Interrupt

Endpoint
Interrupt

USB General
Interrupt Vector

USB Endpoint/Pipe
Interrupt Vector

The macro distinguishes between USB General events in opposition with USB Endpoints events
that are relevant with data transfers relatives to each endpoint.

Figure 19-8. USB General interrupt vector sources
UPRSMIUDINT.6

EORSMIUDINT.5

UPRSMEUDIEN.6

EORSMEUDIEN.5

WAKEUPI

UDINT.4
WAKEUPEUDIEN.4
EORSTIUDINT.3

SOFI
UDINT.2

SUSPI
UDINT.0

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USB General
Interrupt Vector

EORSTEUDIEN.3

SOFE
UDIEN.2

SUSPE
UDIEN.0

Asynchronous Interrupt source(allows the CPU to wake up from power down mode)

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AT90USB82/162
Each of these interupts are time-relative events that will be detected only if the USB clock is
enabled (FRZCLK bit set), except for the WAKEUP interrupt that will trigger each time a statechange is detected on the data lines.
This asynchronous interrupt WAKEUP allows to wake-up a device that is in power-down mode,
generally after that the USB has entered the Suspend state.

Figure 19-9. USB Endpoint Interrupt vector sources

Endpoint 4
Endpoint 3
Endpoint 2
Endpoint 1
Endpoint 0
OVERFIUESTAX.6
UNDERFIUESTAX.5
NAKINIUEINTX.6

NAKOUTIUEINTX.4

RXSTPIUEINTX.3

RXOUTIUEINTX.2

FLERREUEIENX.7

NAKINEUEIENX.6

TXSTPEUEIENX.4

TXOUTEUEIENX.3

USB Endpoint
Interrupt Vector
EPINT
UEINT.X

RXOUTEUEIENX.2

STALLEDIUEINTX.1
STALLEDEUEIENX.1
TXINI

UEINTX.0
TXINE

UEIENX.0

Each endpoint has 8 interrupts sources associated with flags, and each source can be enabled
or not to trigger the corresponding endpoint interrupt.
If, for an endpoint, at least one of the sources is enabled to trigger interrupt, the corresponding
event(s) will make the program branch to the USB Endpoint Interrupt vector. The user may
determine the source (endpoint) of the interrupt by reading the UEINT register, and then handle
the event detected by polling the different flags.

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19.5

Power modes

19.5.1

Idle mode
In this mode, the CPU core is halted (CPU clock stopped). The Idle mode is taken wether theUSB controller is running or not. The CPU can wake up on any USB interrupts.

19.5.2

Power down
In this mode, the oscillator is stopped and halts all the clocks (CPU and peripherals). The USB
controller “wakes up” when:• the WAKEUPI interrupt is triggered (single asynchronous interrupt)

19.5.3Freeze clock
The firmware has the ability to reduce the power consumption by setting the FRZCLK bit, whichfreeze the clock of USB controller. When FRZCLK is set, it is still possible to access to the following registers:• USBCON,• DPRAM direct access registers (DPADD7:0, UEDATX)• UDCON (detach, ...)• UDINT• UDIEN
Moreover, when FRZCLK is set, only the asynchronous interrupt may be triggered :• WAKEUPI

19.6

Memory management
The controller does only support the following memory allocation management.
The reservation of an Endpoint can only be made in the increasing order (Endpoint 0 to the last
Endpoint). The firmware shall thus configure them in the same order.
The reservation of an Endpoint “ki” is done when its ALLOC bit is set. Then, the hardware allocates the memory and insert it between the Endpoints “ki-1 ” and “k i+1”. The “k i+1 ” Endpoint
memory “slides” up and its data is lost. Note that the “ki+2” and upper Endpoint memory does not
slide.
Clearing an Endpoint enable (EPEN) does not clear either its ALLOC bit, or its configuration(EPSIZE/PSIZE, EPBK/PBK). To free its memory, the firmware should clear ALLOC. Then, the“ki+1” Endpoint memory automatically “slides” down. Note that the “k i+2” and upper Endpoint
memory does not slide.
The following figure illustrates the allocation and reorganization of the USB memory in a typicalexample:190

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Table 19-1.

Allocation and reorganization USB memory flow

Free memory

Free memory

Free memory

Free memory

4

4

4

4

Lost memory

3

EPEN=0(ALLOC=1)

3

2 (bigger size)

1

1

1

1

0

0

0

0

Endpoints
activation

Endpoint Disable

Free its memory(ALLOC=0)

Endpoint
Activatation

3

3

2

Conflict

EPEN=1
ALLOC=1• First, Endpoint 0 to Endpoint 4 are configured, in the growing order. The memory of each isreserved in the DPRAM.
• Then, the Endpoint 2is disabled (EPEN=0), but its memory reservation is internally kept by
the controller.
• Its ALLOC bit is cleared: the Endpoint 3 “slides” down, but the Endpoint 4 does not “slide”.
• Finally, the firmware chooses to reconfigure the Endpoint 2, but with a bigger size. The
controller reserved the memory after the endpoint 1 memory and automatically “slide” theEndpoint 3. The Endpoint 4 does not move and a memory conflict appear, in that both
Endpoint 3 and 4 use a common area. The data of those endpoints are potentially lost.
Note that :• the data of Endpoint 0 are never lost whatever the activation or deactivation of the higher
Endpoint. Its data is lost if it is deactivated.
• Deactivate and reactivate the same Endpoint with the same parameters does not lead to a“slide” of the higher endpoints. For those endpoints, the data are preserved.
• CFGOK is set by hardware even in the case that there is a “conflict” in the memory allocation.

19.7

PAD suspend
The next figures illustrates the pad behaviour:• In the “idle” mode, the pad is put in low power consumption mode.
• In the “active” mode, the pad is working.

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Figure 19-10. Pad behaviour

USBE=1& DETACH=0& suspend

Idle mode

USBE=0| DETACH=1| suspend

Active mode

The SUSPI flag indicated that a suspend state has been detected on the USB bus. This flag
automatically put the USB pad in Idle. The detection of a non-idle event sets the WAKEUPI flag
and wakes-up the USB pad.

SUSPI

Suspend detected = USB pad power down

WAKEUPI

Clear Suspend by software

Clear Resume by software
Resume = USB pad wake-up

PAD status
ActivePower Down

ActiveMoreover, the pad can also be put in the “idle” mode if the DETACH bit is set. It come back in
the active mode when the DETACH bit is cleared.

19.8

D+/D- Read/write
The level of D+ and D- can be read and written using the UPOE register. The USB controller has
to be enabled to write a value. For read operation, the USB controller can be enabled or
disabled.

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19.9

Registers description

19.9.1

USB general registers
Bit

7

6

5

4

3

2

1

0

USBE

-

FRZLK

-

-

-

-

-

Read/Writ
e

R/W

R

R/W

R

R

R

R

R

Initial Value

0

0

1

0

0

0

0

0

USBCON

• 7 – USBE: USB macro Enable Bit
Set to enable the USB controller. Clear to disable and reset the USB controller, to disable theUSB transceiver and to disable the USB controller clock inputs.
• 6 – Reserved
The value read from this bit is always 0. Do not set this bit.
• 5 – FRZCLK: Freeze USB Clock Bit
Set to disable the clock inputs (the ”Resume Detection” is still active). This reduces the power
consumption. Clear to enable the clock inputs.
• 4-0 – Reserved
The value read from these bits is always 0. Do not set these bits.

Bit

7

6

5

4

3

2

1

0

DPACC

-

-

-

-

-

-

-

Read/Wr
ite

R/W

R

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0

UDPADDH

• 7 – DPACC: DPRAM Direct Access Bit
Set this bit to directly read the content the Dual-Port RAM (DPR) data through the UEDATX or
UPDATX registers. See Section 19.6, page 190 for more details.
Clear this bit for normal operation and access the DPR through the endpoint FIFO.
• 6-0 – Reserved
The value read from these bits is always 0. Do not set these bits.

Bit

7

6

5

4

3

2

1

0

DPADD7:0

UDPADDL

Read/Wr
ite

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial
Value

0

0

0

0

0

0

0

0

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• 7-0 – DPADD7:0: DPRAM Address Low Bit
DAPDD7:0 is the least significant part of DPADD.

19.9.2

USB/PS2 Software Output Enable register – UPOE
Bit

7

6

5

4

3

2

1

0

UPWE1

UPWE0

UPDRV
1

UPDRV
0

SCKI

DATAI

DPI

DMI

Read/Write

R/W

R/W

R/W

R/W

R

R

R

R

Initial Value

0

0

0

0

0

0

0

0

UPOE

• Bit 7:6 – UPOE[1:0]: USB/PS2 Output enable
Set these bits with the following configuration to enable or disable the USB/PS2 software drive.
UPOE1 - UPOE0
0 - 0 : Direct drive is disabled.
0 - 1 : Reserved
1 - 0 : Direct drive of DP/DM with USB levels (UPDRV[1:0] values)
1 - 1 : Direct drive of DP/DM with PS/2 levels (UPDRV[1:0] values)• Bit 5:4 – UPDRV[1:0] : USB/PS2 direct drive values
Write in UPDRV1 the value to write on D+/SCK following the UPOE[1:0] configuration.
Write in UPDRV0 the value to write on D-/DATA following the UPOE[1:0] configuration.
• Bit 3 – SCKI : SCK Input value
This bit is set to one by hardware if a ‘1’ is read on SCK (PS/2 pad).
This bit is set to zero by hardware if a ‘0’ is read on SCK (PS/2 pad).
• Bit 2 – DATAI : DATA Input value
This bit is set to one by hardware if a ‘1’ is read on DATA (PS/2 pad).
This bit is set to zero by hardware if a ‘0’ is read on DATA (PS/2 pad).
• Bit 1 – DPI : D+ Input value
This bit is set to one by hardware if a ‘1’ is read on D+ (USB pad).
This bit is set to zero by hardware if a ‘0’ is read on D+ (USB pad).
• Bit 0 – DMI : D- Input value
This bit is set to one by hardware if a ‘1’ is read on D- (USB pad).
This bit is set to zero by hardware if a ‘0’ is read on D- (USB pad).

19.10 USB Software Operating modes
Depending on the USB operating mode, the software should perform some the following
operations:Power On the USB interface• Configure PLL interface• Enable PLL• Check PLL lock194

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AT90USB82/162• Enable USB interface• Configure USB interface (USB Endpoint 0 configuration)• Attach USB device
Power Off the USB interface• Detach USB device• Disable USB interface• Disable PLL
Suspending the USB interface• Clear Suspend Bit• Set USB suspend clock• Disable PLL• Be sure to have interrupts enabled (WAKEUPE) to exit sleep mode
• Put the MCU in sleep mode
Resuming the USB interface• Enable PLL• Wait PLL lock• Clear USB suspend clock• Clear Resume information

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20. USB Device Operating modes
20.1

Introduction
The USB device controller supports full speed data transfers. In addition to the default control
endpoint, it provides four other endpoints, which can be configured in control, bulk, interrupt or
isochronous modes:• Endpoint 0:programmable size FIFO up to 64 bytes, default control endpoint• Endpoints 1and 2:programmable size FIFO up to 64 bytes.
• Endpoints 3 and 4: programmable size FIFO up to 64 bytes with ping-pong mode.
The controller starts in the “idle” mode. In this mode, the pad consumption is reduced to theminimum.

20.2

Power-on and reset
The next diagram explains the USB device controller main states on power-on:
Figure 20-1. USB device controller states after reset

USBE=0<any
otherstate>

USBE=0Reset

Idle

USBE=1
UID=1

HW
RESET

The reset state of the Device controller is:• the macro clock is stopped in order to minimize the power consumption (FRZCLK set),• the USB device controller internal state is reset (all the registers are reset to their default
value. Note that DETACH is set.)• the endpoint banks are reset• the D+ pull up are not activated (mode Detach)
The D+ pull-up will be activated as soon as the DETACH bit is cleared.
The macro is in the ‘Idle’ state after reset with a minimum power consumption and does notneed to have the PLL activated to enter in this state.
The USB device controller can at any time be reset by clearing USBE.

20.3

Endpoint reset
An endpoint can be reset at any time by setting in the UERST register the bit corresponding to
the endpoint (EPRSTx). This resets:• the internal state machine on that endpoint,• the Rx and Tx banks are cleared and their internal pointers are restored,

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AT90USB82/162• the UEINTX, UESTA0X and UESTA1X are restored to their reset value.
The data toggle field remains unchanged.
The other registers remain unchanged.
The endpoint configuration remains active and the endpoint is still enabled.
The endpoint reset may be associated with a clear of the data toggle command (RSTDT bit) as
an answer to the CLEAR_FEATURE USB command.

20.4

USB reset
When an USB reset is detected on the USB line (SEO state with a minimal duration of 100µs),
the next operations are performed by the controller:• all the endpoints are disabled• the default control endpoint remains configured• The data toggle of the default control endpoint is cleared.
If the hardware reset function is selected, a reset is generated to the CPU core without disabling
the USB controller (that remains in the same state than after a USB Reset).

20.5

Endpoint selection
Prior to any operation performed by the CPU, the endpoint must first be selected. This is doneby setting the EPNUM2:0 bits (in UENUM register) with the endpoint number which will be managed by the CPU.
The CPU can then access to the various endpoint registers and data.

20.6

Endpoint activation
The endpoint is maintained under reset as long as the EPEN bit is not set.
The following flow must be respected in order to activate an endpoint:

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Figure 20-2. Endpoint activation flow:
Endpoint
Activation

UENUM

Select the endpoint

EPEN=1

Activate the endpoint

UECFG0X

Configure:- the endpoint direction- the endpoint type- the Not Yet Disable feature

UECFG1X

Configure:- the endpoint size
- the bank parametrization
Allocation and reorganization of
the memory is made on-the-fly

EPNUM=x

EPDIR
EPTYPE...

ALLOC
EPSIZEEPBKCFGOK=1
Yes
Endpoint activatedTest the correct endpoint
configuration

No

ERROR

As long as the endpoint is not correctly configured (CFGOK cleared), the hardware does not
acknowledge the packets sent by the host.
CFGOK will not be set if the Endpoint size parameter is bigger than the DPRAM size.
A clear of EPEN acts as an endpoint reset (see Section 20.3, page 196 for more details). It also
performs the next operation:• The configuration of the endpoint is kept (EPSIZE, EPBK, ALLOC kept)• It resets the data toggle field.
• The DPRAM memory associated to the endpoint is still reserved.
See Section 19.6, page 190 for more details about the memory allocation/reorganization.

20.7

Address Setup
The USB device address is set up according to the USB protocol:• the USB device, after power-up, responds at address 0• the host sends a SETUP command (SET_ADDRESS(addr)),• the firmware records that address in UADD, but keep ADDEN cleared,• the USB device sends an IN command of 0 bytes (IN 0 Zero Length Packet) to acknowledge
the transaction,• then, the firmware may enable the USB device address by setting ADDEN. The only
accepted address by the controller is the one stored in UADD.
ADDEN and UADD shall not be written at the same time.
UADD contains the default address 00h after a power-up or an USB reset.

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AT90USB82/162
ADDEN is cleared by hardware:• after a power-up reset,• when an USB reset is received,• or when the macro is disabled (USBE cleared)
When this bit is cleared, the default device address 00h is used.

20.8

Suspend, Wake-up and Resume
After a period of 3 ms during which the USB line was inactive (J state), the controller setn the
SUSPI flag and triggers the corresponding interrupt if enabled. The firmware may then set the
FRZCLK bit.
The CPU can also, depending on software architecture, disable the PLL and/or enter in the idle
mode to reduce the power consumption (especially in a bus powered application).
There are two ways to recover from the “Suspend” mode:• First one is to clear the FRZCLK bit. This is possible if the CPU is not in the Idle mode.
• Second way, if the CPU is “idle”, is to enable the WAKEUPI interrupt (WAKEUPE set). Then,as soon as an non-idle signal is seen by the controller, the WAKEUPI interrupt is triggered.
The firmware shall then clear the FRZCLK bit to restart the transfer.
There are no relationship between the SUSPI interrupt and the WAKEUPI interrupt: the WAKEUPI interrupt is triggered as soon as there are non-idle patterns on the data lines. Thus, the
WAKEUPI interrupt can occurs even if the controller is not in the “suspend” mode.
When the WAKEUPI interrupt is triggered, if the SUSPI interrupt bit was already set, it is clearedby hardware.
When the SUSPI interrupt is triggered, if the WAKEUPI interrupt bit was already set, it is clearedby hardware.

20.9

DetachThe reset value of the DETACH bit is 1.
It is possible to re-enumerate a device, simply by setting and clearing the DETACH bit (the linedischarge time must be taken in account).
• When the USB device controller is in full-speed mode, setting DETACH will disconnect thepull-up on the D+ . Then, clearing DETACH will connect the pull-up on the D+.
Figure 20-3. Detach a device in Full-speed:
UVREF

UVREF

EN=1

D+

D+

D-

DDetach, thenAttachEN=1

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20.10 Remote Wake-up
The “Remote Wake-up” (or “upstream resume”) request is the only operation allowed to be sentby the device on its own initiative. Anyway, to do that, the device should first have received a
DEVICE_REMOTE_WAKEUP request from the host.
• First, the USB controller must have detected the “suspend” state of the line: the remotewake-up can only be sent if the SUSPI bit is set.
• The firmware has then the ability to set RMWKUP to send the “upstream resume” stream.
This will automatically be done by the controller after 5ms of inactivity on the USB line.
• When the controller starts to send the “upstream resume”, the UPRSMI flag is set andinterrupt is triggered (if enabled). If SUSPI was set, SUSPI is cleared by hardware.
• RMWKUP is automatically cleared by hardware at the end of the “upstream resume”.
• After that, if the controller detects a good “End Of Resume” signal from the host, an EORSMI
interrupt is triggered (if enabled).

20.11 STALL request
For each endpoint, the STALL management is performed using 2 bits:– STALLRQ (enable stall request)– STALLRQC (disable stall request)– STALLEDI (stall sent interrupt)
To send a STALL handshake at the next request, the STALLRQ request bit has to be set. All following requests will be handshak’ed with a STALL until the STALLRQC bit is set.
Setting STALLRQC automatically clears the STALLRQ bit. The STALLRQC bit is also immediately cleared by hardware after being set by software. Thus, the firmware will never read this bit
as set.
Each time the STALL handshake is sent, the STALLEDI flag is set by the USB controller and the
EPINTx interrupt will be triggered (if enabled).
The incoming packets will be discarded (RXOUTI and RWAL will not be set).
The host will then send a command to reset the STALL: the firmware just has to set the STALLRQC bit and to reset the endpoint.
20.11.1

Special consideration for Control Endpoints
A SETUP request is always ACK’ed.
If a STALL request is set for a Control Endpoint and if a SETUP request occurs, the SETUP
request has to be ACK’ed and the STALLRQ request and STALLEDI sent flags are automatically reset (RXSETUPI set, TXIN cleared, STALLED cleared, TXINI cleared...).
This management simplifies the enumeration process management. If a command is not supported or contains an error, the firmware set the STALL request flag and can return to the maintask, waiting for the next SETUP request.
Th is fu nc t io n i s c o mp l ia nt wi th t he C ha pt er 8 t es t t ha t s en ds ex t r a s ta tu s fo r a
GET_DESCRIPTOR. The firmware sets the STALL request just after receiving the status. All
extra status will be automatically STALL’ed until the next SETUP request.

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20.11.2

STALL handshake and Retry mechanism
The Retry mechanism has priority over the STALL handshake. A STALL handshake is sent if the
STALLRQ request bit is set and if there is no retry required.

20.12 CONTROL endpoint management
A SETUP request is always ACK’ed. When a new setup packet is received, the RXSTPI interrupt is triggered (if enabled). The RXOUTI interrupt is not triggered.
The FIFOCON and RWAL fields are irrelevant with CONTROL endpoints. The firmware shallthus never use them on that endpoints. When read, their value is always 0.
CONTROL endpoints are managed by the following bits:• RXSTPI is set when a new SETUP is received. It shall be cleared by firmware toacknowledge the packet and to clear the endpoint bank.
• RXOUTI is set when a new OUT data is received. It shall be cleared by firmware toacknowledge the packet and to clear the endpoint bank.
• TXINI is set when the bank is ready to accept a new IN packet. It shall be cleared by firmware
to send the packet and to clear the endpoint bank.
CONTROL endpoints should not be managed by interrupts, but only by polling the status bits.
20.12.1

Control Write
The next figure shows a control write transaction. During the status stage, the controller will notnecessary send a NAK at the first IN token:• If the firmware knows the exact number of descriptor bytes that must be read, it can thenanticipate on the status stage and send a ZLP for the next IN token,• or it can read the bytes and poll NAKINI, which tells that all the bytes have been sent by thehost, and the transaction is now in the status stage.

SETUP
USB line
RXSTPIRXOUTI
TXINI

DATA

SETUP
HW

OUT

STATUS

OUT

IN

IN

NAK

SW
HW

SW

HW

SW
SW

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20.12.2

Control Read
The next figure shows a control read transaction. The USB controller has to manage the simultaneous write requests from the CPU and the USB host:

SETUP
USB line
RXSTPI

DATA

SETUP
HW

IN

STATUSIN

OUT

SW

RXOUTI
TXINI

OUT

NAK
HW
SW

HW

SW

SW

Wr Enable
HOST
Wr EnableCPU

A NAK handshake is always generated at the first status stage command.
When the controller detect the status stage, all the data writen by the CPU are erased, andclearing TXINI has no effects.
The firmware checks if the transmission is complete or if the reception is complete.
The OUT retry is always ack’ed. This reception:- set the RXOUTI flag (received OUT data)- set the TXINI flag (data sent, ready to accept new data)
software algorithm:

set transmit readywait (transmit complete OR Receive complete)
if receive complete, clear flag and return
if transmit complete, continue

Once the OUT status stage has been received, the USB controller waits for a SETUP request.
The SETUP request have priority over any other request and has to be ACK’ed. This means thatany other flag should be cleared and the fifo reset when a SETUP is received.
WARNING: the byte counter is reset when a OUT Zero Length Packet is received. The firmware
has to take care of this.

20.13 OUT endpoint management
OUT packets are sent by the host. All the data can be read by the CPU, which acknowledges or
not the bank when it is empty.

20.13.1

Overview
The Endpoint must be configured first.

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AT90USB82/162
20.13.1.1“Manual” mode
Each time the current bank is full, the RXOUTI and the FIFOCON bits are set. This triggers aninterrupt if the RXOUTE bit is set. The firmware can acknowledge the USB interrupt by clearing
the RXOUTI bit. The Firmware read the data and clear the FIFOCON bit in order to free the current bank. If the OUT Endpoint is composed of multiple banks, clearing the FIFOCON bit willswitch to the next bank. The RXOUTI and FIFOCON bits are then updated by hardware inaccordance with the status of the new bank.
RXOUTI shall always be cleared before clearing FIFOCON.
The RWAL bit always reflects the state of the current bank. This bit is set if the firmware canread data from the bank, and cleared by hardware when the bank is empty.

Example with 1 OUT data bank
OUT

DATA
(to bank 0)

NAK

ACK

OUT

DATA
(to bank 0)

ACK

HW
RXOUTI

HW
SW

SW

read data from CPU
BANK 0

FIFOCONSW

read data from CPU
BANK 0

Example with 2 OUT data banks
OUT

DATA
(to bank 0)

ACK

OUT

DATA
(to bank 1)

ACK

HW
RXOUTI

FIFOCON

20.13.2

HW

SW

read data from CPU
BANK 0SW

SW

read data from CPU
BANK 1

Detailed description
The data are read by the CPU, following the next flow:• When the bank is filled by the host, an endpoint interrupt (EPINTx) is triggered, if enabled(RXOUTE set) and RXOUTI is set. The CPU can also poll RXOUTI or FIFOCON, dependingon the software architecture,• The CPU acknowledges the interrupt by clearing RXOUTI,• The CPU can read the number of byte (N) in the current bank (N=BYCT),• The CPU can read the data from the current bank (“N” read of UEDATX),

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• The CPU can free the bank by clearing FIFOCON when all the data is read, that is:• after “N” read of UEDATX,• as soon as RWAL is cleared by hardware.
If the endpoint uses 2 banks, the second one can be filled by the HOST while the current one isbeing read by the CPU. Then, when the CPU clear FIFOCON, the next bank may be already
ready and RXOUTI is set immediately.

20.14 IN endpoint management
IN packets are sent by the USB device controller, upon an IN request from the host. All the data
can be written by the CPU, which acknowledge or not the bank when it is full.Overview
The Endpoint must be configured first.
20.14.0.1“Manual” mode
The TXINI bit is set by hardware when the current bank becomes free. This triggers an interrupt
if the TXINE bit is set. The FIFOCON bit is set at the same time. The CPU writes into the FIFO
and clears the FIFOCON bit to allow the USB controller to send the data. If the IN Endpoint iscomposed of multiple banks, this also switches to the next data bank. The TXINI and FIFOCON
bits are automatically updated by hardware regarding the status of the next bank.
TXINI shall always be cleared before clearing FIFOCON.

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AT90USB82/162
The RWAL bit always reflects the state of the current bank. This bit is set if the firmware canwrite data to the bank, and cleared by hardware when the bank is full.
Example with 1 IN data bank

NAK

DATA
(bank 0)

IN

ACK

IN

HW
TXINI

FIFOCONSW

SW

write data from CPU
BANK 0SW

write data from CPU
BANK 0SW

Example with 2 IN data banks

DATA(bank 0)

IN

ACK

IN

DATA
(bank 1)

ACK

HW
TXINI

FIFOCON

20.14.1

SWSW

write data from CPU
BANK 0SW

write data from CPU
BANK 1SWSW

write data from CPU
BANK0

Detailed description
The data are written by the CPU, following the next flow:• When the bank is empty, an endpoint interrupt (EPINTx) is triggered, if enabled (TXINE set)
and TXINI is set. The CPU can also poll TXINI or FIFOCON, depending the softwarearchitecture choice,• The CPU acknowledges the interrupt by clearing TXINI,• The CPU can write the data into the current bank (write in UEDATX),• The CPU can free the bank by clearing FIFOCON when all the data are written, that is:• after “N” write into UEDATX• as soon as RWAL is cleared by hardware.
If the endpoint uses 2 banks, the second one can be read by the HOST while the current isbeing written by the CPU. Then, when the CPU clears FIFOCON, the next bank may be already
ready (free) and TXINI is set immediately.

20.14.1.1

Abort
An “abort” stage can be produced by the host in some situations:

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• In a control transaction: ZLP data OUT received during a IN stage,• In an isochronous IN transaction: ZLP data OUT received on the OUT endpoint during a IN
stage on the IN endpoint• ...
The KILLBK bit is used to kill the last “written” bank. The best way to manage this abort is to perform the following operations:

Table 20-1.

Abort flow
Endpoint
Abort
Clear
UEIENX.
TXINE
NBUSYBK=0
Yes

Disable the TXINI interrupt.

Abort is based on the factthat no banks are busy,
meaning that nothing has tobe sent.

No

Endpoint
reset
Yes

KILLBK=1

Kill the last written
bank.

KILLBK=1

Wait for the end of theprocedure.

No

Abort done

20.15 Isochronous mode
20.15.1

Underflow
An underflow can occur during IN stage if the host attempts to read a bank which is empty. In
this situation, the UNDERFI interrupt is triggered.
An underflow can also occur during OUT stage if the host send a packet while the banks are
already full. Typically, he CPU is not fast enough. The packet is lost.
It is not possible to have underflow error during OUT stage, in the CPU side, since the CPU
should read only if the bank is ready to give data (RXOUTI=1 or RWAL=1)

20.15.2

CRC Error
A CRC error can occur during OUT stage if the USB controller detects a bad received packet. In
this situation, the STALLEDI interrupt is triggered. This does not prevent the RXOUTI interrupt
from being triggered.

20.16 Overflow
In Control, Isochronous, Bulk or Interrupt Endpoint, an overflow can occur during OUT stage, if
the host attempts to write in a bank that is too small for the packet. In this situation, the OVERFIinterrupt is triggered (if enabled). The packet is hacknowledged and the RXOUTI interrupt is also
triggered (if enabled). The bank is filled with the first bytes of the packet.

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It is not possible to have overflow error during IN stage, in the CPU side, since the CPU should
write only if the bank is ready to access data (TXINI=1 or RWAL=1).

20.17 Interrupts
The next figure shows all the interrupts sources:

Figure 20-4. USB Device Controller Interrupt System
UPRSMIUDINT.6

EORSMIUDINT.5

UPRSMEUDIEN.6

EORSMEUDIEN.5

WAKEUPI

UDINT.4
WAKEUPEUDIEN.4
EORSTIUDINT.3

SOFI
UDINT.2

SUSPI
UDINT.0

USB Device
Interrupt

EORSTEUDIEN.3

SOFE
UDIEN.2

SUSPE
UDIEN.0

There are 2 kind of interrupts: processing (i.e. their generation are part of the normal processing)and exception (errors).
Processing interrupts are generated when:• Upstream resume(UPRSMI)• End of resume(EORSMI)• Wake up(WAKEUPI)• End of reset (Speed Initialization)(EORSTI)• Start of frame(SOFI, if FNCERR=0)• Suspend detected after 3 ms of inactivity(SUSPI)
Exception Interrupts are generated when:• CRC error in frame number of SOF(SOFI, FNCERR=1)

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Figure 20-5. USB Device Controller Endpoint Interrupt System
Endpoint 4
Endpoint 3
Endpoint 2
Endpoint 1
Endpoint 0
OVERFIUESTAX.6
UNDERFIUESTAX.5

FLERREUEIENX.7

NAKINIUEINTX.6

NAKINEUEIENX.6

NAKOUTIUEINTX.4

TXSTPEUEIENX.4

RXSTPIUEINTX.3

Endpoint Interrupt
EPINT
UEINT.X

TXOUTEUEIENX.3

RXOUTIUEINTX.2

RXOUTEUEIENX.2

STALLEDIUEINTX.1
STALLEDEUEIENX.1
TXINI

UEINTX.0
TXINE

UEIENX.0

Processing interrupts are generated when:• Ready to accept IN data(EPINTx, TXINI=1)• Received OUT data(EPINTx, RXOUTI=1)• Received SETUP(EPINTx, RXSTPI=1)
Exception Interrupts are generated when:• Stalled packet(EPINTx, STALLEDI=1)• CRC error on OUT in isochronous mode(EPINTx, STALLEDI=1)• Overflow(EPINTx, OVERFI=1)• Underflow in isochronous mode(EPINTx, UNDERFI=1)• NAK IN sent(EPINTx, NAKINI=1)• NAK OUT sent(EPINTx, NAKOUTI=1)

20.18 Registers
20.18.1

USB device general registers
Bit

208

7

6

5

4

3

2

1

-

-

-

-

-

RSTCPURMWKUP

DETACH

Read/Wri R
te

R

R

R

R

R/W

R/W

R/W

Initial
Value

0

0

0

0

0

0

1

0

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0
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AT90USB82/162• Bit 2- RSTCPU - USB Reset CPU Bit
Set this bit to one by firmware in order to reset the CPU at the next USB reset (without disabling
the USB controller). The value of this bit will not be affected by the reset of the CPU generated
by a End Of Reset (remains set). This bit is reset when the USB controller is disabled.
Set this bit to zero by firmware otherwise.

• Bit 1- RMWKUP - Remote Wake-up Bit
Set to send an “upstream-resume” to the host for a remote wake-up. The SUSPI bit must be set
to allow the remote wake up to be sent.
Cleared by hardware. Clearing by software has no effect.
See Section 20.10, page 200 for more details.

• Bit 0 - DETACH - Detach Bit
Set to physically detach de device.
Clear to reconnect the device. See Section 20.9, page 199 for more details.

Bit

7

6

5

4

3

2

1

0

-

UPRSMIEORSMI

WAKEUPIEORSTI

SOFI

-

SUSPI

Read/Wri R
te

R/W

R/W

R/W

R/W

R/W

R

R/W

Initial
Value

0

0

0

0

0

0

0

0

UDINT

• 7 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 6 - UPRSMI - Upstream Resume Interrupt Flag
Set by hardware when the USB controller is sending a resume signal called “Upstream
Resume”. This triggers an USB interrupt if UPRSME is set.
Shall be cleared by software (USB clocks must be enabled before). Setting by software has noeffect.

• 5 - EORSMI - End Of Resume Interrupt Flag
Set by hardware when the USB controller detects a good “End Of Resume” signal initiated by
the host. This triggers an USB interrupt if EORSME is set.
Shall be cleared by software. Setting by software has no effect.

• 4 - WAKEUPI - Wake-up CPU Interrupt Flag
Set by hardware when the USB controller is re-activated by a filtered non-idle signal from thelines (not by an upstream resume). This triggers an interrupt if WAKEUPE is set.
Shall be cleared by software (USB clock inputs must be enabled before). Setting by software
has no effect.
See Section 20.8, page 199 for more details.

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• 3 - EORSTI - End Of Reset Interrupt Flag
Set by hardware when an “End Of Reset” has been detected by the USB controller. This triggers
an USB interrupt if EORSTE is set.
Shall be cleared by software. Setting by software has no effect.

• 2 - SOFI - Start Of Frame Interrupt Flag
Set by hardware when an USB “Start Of Frame” PID (SOF) has been detected (every 1 ms).
This triggers an USB interrupt if SOFE is set..
• 1 - Reserved• 0 - SUSPI - Suspend Interrupt Flag
Set by hardware when an USB “Suspend” ‘idle bus for 3 frame periods: a J state for 3 ms) is
detected. This triggers an USB interrupt if SUSPE is set.
Shall be cleared by software. Setting by software has no effect.
See Section 20.8, page 199 for more details.
The interrupt flags bits are set even if their corresponding ‘Enable’ bits is not set.

Bit

7

6

5

4

3

2

1

0

-

UPRSMEEORSME

WAKEUPEEORSTE

SOFE

-

SUSPE

Read/Wri R
te

R/W

R/W

R/W

R/W

R/W

R

R/W

Initial
Value

0

0

0

0

0

0

0

0

UDIEN

• 7 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 6 - UPRSME - Upstream Resume Interrupt Enable Bit
Set to enable the UPRSMI interrupt.
Clear to disable the UPRSMI interrupt.

• 5 - EORSME - End Of Resume Interrupt Enable Bit
Set to enable the EORSMI interrupt.
Clear to disable the EORSMI interrupt.

• 4 - WAKEUPE - Wake-up CPU Interrupt Enable Bit
Set to enable the WAKEUPI interrupt.
Clear to disable the WAKEUPI interrupt.

• 3 - EORSTE - End Of Reset Interrupt Enable Bit
Set to enable the EORSTI interrupt. This bit is set after a reset.
Clear to disable the EORSTI interrupt.

• 2 - SOFE - Start Of Frame Interrupt Enable Bit
Set to enable the SOFI interrupt.

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Clear to disable the SOFI interrupt.

• 1 - Reserved• 0 - SUSPE - Suspend Interrupt Enable Bit
Set to enable the SUSPI interrupt.
Clear to disable the SUSPI interrupt.

Bit

7

6

ADDEN

UADD6:0

5

4

3

2

1

0
UDADDR

Read/Wri R/W
te

R/W

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

1

0

0

• 7 - ADDEN - Address Enable Bit
Set to activate the UADD (USB address).
Cleared by hardware. Clearing by software has no effect.
See Section 20.7, page 198 for more details.

• 6-0 - UADD6:0 - USB Address Bits
Set to configure the device address.
Shall not be cleared.

Bit

7

6

5

4

3

2

-

-

-

-

-

FNUM10:8

Read/Wri R
te

R

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0

UDFNUMH• 7-3 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 2-0 - FNUM10:8 - Frame Number Upper Flag
Set by hardware. These bits are the 3 MSB of the 11-bits Frame Number information. They areprovided in the last received SOF packet. FNUM is updated if a corrupted SOF is received.

Bit

7

6

5

4

3

2

1

0

Read/Wri R
te

R

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

FNUM7:00

UDFNUML

• 7-0 Frame Number Lower Flag
Set by hardware. These bits are the 8 LSB of the 11-bits Frame Number information.

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Bit

7

6

5

4

3

2

1

0

-

-

-

FNCERR----

Read/Wri R
te

R

R

R/W

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0

UDMFN

• 7-5 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 4 - FNCERR -Frame Number CRC Error Flag
Set by hardware when a corrupted Frame Number in start of frame packet is received.
This bit and the SOFI interrupt are updated at the same time.

• 3-0 - Reserved
The value read from these bits is always 0. Do not set these bits.
20.18.2

USB device endpoint registers
Bit

7

6

5

4

3

2

-

-

-

-

-

EPNUM2:0

Read/Wri R
te

R

R

R

R

Initial
Value

0

0

0

0

0

1

0

R/W

R/W

R/W

0

0

0

UENUM

• 7-3 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 2-0 - EPNUM2:0 Endpoint Number Bits
Set to select the number of the endpoint which shall be accessed by the CPU. See Section 20.5,
page 197 for more details.
Values greater than 100b are forbidden.

Bit

7

6

5

4

3

2

1

0

-

-

-

EPRST D4

EPRST D3

EPRST D2

EPRST D1

EPRST D0

Read/Wri R
te

R

R

R/W

R/W

R/W

R/W

R/W

Initial
Value

0

0

0

0

0

0

0

0

UERST

• 7-5 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 4-0 - EPRST4:0 - Endpoint FIFO Reset Bits
Set to reset the selected endpoint FIFO prior to any other operation, upon hardware reset or
when an USB bus reset has been received. See Section 20.3, page 196 for more information

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AT90USB82/162
Then, cleared by software to complete the reset operation and start using the FIFO.

Bit

7

6

5

4

2

1

0

-

-

STALLRQ

STALLRQC RSTDT

-

-

EPEN

Read/Wri R
te

R

R/W

R/W

R/W

R

R

R/W

Initial
Value

0

0

0

0

0

0

0

0

3

UECONX• 7-6 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 5 - STALLRQ - STALL Request Handshake Bit
Set to request a STALL answer to the host for the next handshake.
Cleared by hardware when a new SETUP is received. Clearing by software has no effect.
See Section 20.11, page 200 for more details.

• 4 - STALLRQC - STALL Request Clear Handshake Bit
Set to disable the STALL handshake mechanism.
Cleared by hardware immediately after the set. Clearing by software has no effect.
See Section 20.11, page 200 for more details.
3• RSTDT - Reset Data Toggle Bit
Set to automatically clear the data toggle sequence:
For OUT endpoint: the next received packet will have the data toggle 0.
For IN endpoint: the next packet to be sent will have the data toggle 0.
Cleared by hardware instantaneously. The firmware does not have to wait that the bit is cleared.
Clearing by software has no effect.

• 2 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 1 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 0 - EPEN - Endpoint Enable Bit
Set to enable the endpoint according to the device configuration. Endpoint 0 shall always beenabled after a hardware or USB reset and participate in the device configuration.
Clear this bit to disable the endpoint. See Section 20.6, page 197 for more details.

Bit

7

6

EPTYPE1:0
Read/Wri R/W
te

R/W

5

4

3

2

1

0

-

-

-

-

-

EPDIR

R

R

R

R

R

R/W

UECFG0X

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Bit

7

6

5

4

3

2

1

0

Initial
Value

0

0

0

0

0

0

0

0

• 7-6 - EPTYPE1:0 - Endpoint Type Bits
Set this bit according to the endpoint configuration:
00b: Control10b: Bulk
01b: Isochronous11b: Interrupt• 5-1 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 0 - EPDIR - Endpoint Direction Bit
Set to configure an IN direction for bulk, interrupt or isochronous endpoints.
Clear to configure an OUT direction for bulk, interrupt, isochronous or control endpoints.

Bit

7

6

-

EPSIZE2:0

5

4

3

2

EPBK1:0

1

0

ALLOC

-

Read/Wri R
te

R/W

R/W

R/W

R/W

R/W

R/W

R

Initial
Value

0

0

0

0

0

0

0

0

UECFG1X• 7 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 6-4 - EPSIZE2:0 - Endpoint Size Bits
Set this bit according to the endpoint size:
000b: 8 bytes
001b: 16 bytes
010b: 32 bytes
011b: 64 bytes
Other : Reserved. Do not use this configuration.

• 3-2 - EPBK1:0 - Endpoint Bank Bits
Set this field according to the endpoint size:
00b: One bank
01b: Double bank
1xb: Reserved. Do not use this configuration.

• 1 - ALLOC - Endpoint Allocation Bit
Set this bit to allocate the endpoint memory.
Clear to free the endpoint memory.
See Section 20.6, page 197 for more details.

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AT90USB82/162• 0 - Reserved
The value read from these bits is always 0. Do not set these bits.

Bit

7

6

5

4

3

CFGOK

OVERFIUNDERFI-DTSEQ1:0

Read/Wri R
te

R/W

R/W

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0

2

1

0

NBUSYBK1:0

UESTA0X• 7 - CFGOK - Configuration Status Flag
Set by hardware when the endpoint X size parameter (EPSIZE) and the bank parametrization(EPBK) are correct compared to the max FIFO capacity and the max number of allowed bank.
This bit is updated when the bit ALLOC is set.
If this bit is cleared, the user should reprogram the UECFG1X register with correct EPSIZE andEPBK values.

• 6 - OVERFI - Overflow Error Interrupt Flag
Set by hardware when an overflow error occurs in an isochronous endpoint. An interrupt(EPINTx) is triggered (if enabled).
See Section 20.15, page 206 for more details.
Shall be cleared by software. Setting by software has no effect.

• 5 - UNDERFI - Flow Error Interrupt Flag
Set by hardware when an underflow error occurs in an isochronous endpoint. An interrupt(EPINTx) is triggered (if enabled).
See Section 20.15, page 206 for more details.
Shall be cleared by software. Setting by software has no effect.

• 4- Reserved
The value read from these bits is always 0. Do not set these bits.
• 3-2 - DTSEQ1:0 - Data Toggle Sequencing Flag
Set by hardware to indicate the PID data of the current bank:
00b

Data0

01b

Data1

1xb

Reserved.

For OUT transfer, this value indicates the last data toggle received on the current bank.
For IN transfer, it indicates the Toggle that will be used for the next packet to be sent. This is not
relative to the current bank.

• 1-0 - NBUSYBK1:0 - Busy Bank Flag
Set by hardware to indicate the number of busy bank.
For IN endpoint, it indicates the number of busy bank(s), filled by the user, ready for IN transfer.

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For OUT endpoint, it indicates the number of busy bank(s) filled by OUT transaction from the
host.
00b

All banks are free01b

1 busy bank10b

2 busy banks

11b

Reserved.

Bit

7

6

5

4

3

2

1

-

-

-

-

-

CTRLDIR

CURRBK1:0

Read/Wri R
te

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0
UESTA1X0• 7-3 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 2 - CTRLDIR - Control Direction (Flag, and bit for debug purpose)
Set by hardware after a SETUP packet, and gives the direction of the following packet:- 1 for IN endpoint- 0 for OUT endpoint.
Can not be set or cleared by software.

• 1-0 - CURRBK1:0 - Current Bank (all endpoints except Control endpoint) Flag
Set by hardware to indicate the number of the current bank:
00b

Bank0

01b

Bank1

1xb

Reserved.

Can not be set or cleared by software.

Bit

7

6

5

4

3

2

1

0

FIFOCON

NAKINIRWAL

NAKOUTIRXSTPIRXOUTISTALLEDI

TXINI

Read/Wri R/W
te

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial
Value

0

0

0

0

0

0

0

0

UEINTX• 7 - FIFOCON - FIFO Control Bit
For OUT and SETUP Endpoint:
Set by hardware when a new OUT message is stored in the current bank, at the same time than
RXOUT or RXSTP.
Clear to free the current bank and to switch to the following bank. Setting by software has noeffect.

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For IN Endpoint:
Set by hardware when the current bank is free, at the same time than TXIN.
Clear to send the FIFO data and to switch the bank. Setting by software has no effect.

• 6 - NAKINI - NAK IN Received Interrupt Flag
Set by hardware when a NAK handshake has been sent in response of a IN request from thehost. This triggers an USB interrupt if NAKINE is sent.
Shall be cleared by software. Setting by software has no effect.

• 5 - RWAL - Read/Write Allowed Flag
Set by hardware to signal:- for an IN endpoint: the current bank is not full i.e. the firmware can push data into the FIFO,- for an OUT endpoint: the current bank is not empty, i.e. the firmware can read data from the
FIFO.
The bit is never set if STALLRQ is set, or in case of error.
Cleared by hardware otherwise.
This bit shall not be used for the control endpoint.

• 4 - NAKOUTI - NAK OUT Received Interrupt Flag
Set by hardware when a NAK handshake has been sent in response of a OUT/PING requestfrom the host. This triggers an USB interrupt if NAKOUTE is sent.
Shall be cleared by software. Setting by software has no effect.

• 3 - RXSTPI - Received SETUP Interrupt Flag
Set by hardware to signal that the current bank contains a new valid SETUP packet. An interrupt (EPINTx) is triggered (if enabled).
Shall be cleared by software to handshake the interrupt. Setting by software has no effect.
This bit is inactive (cleared) if the endpoint is an IN endpoint.

• 2 - RXOUTI / KILLBK - Received OUT Data Interrupt Flag
Set by hardware to signal that the current bank contains a new packet. An interrupt (EPINTx) is
triggered (if enabled).
Shall be cleared by software to handshake the interrupt. Setting by software has no effect.

Kill Bank IN Bit
Set this bit to kill the last written bank.
Cleared by hardware when the bank is killed. Clearing by software has no effect.
See page 205 for more details on the Abort.

• 1 - STALLEDI - STALLEDI Interrupt Flag
Set by hardware to signal that a STALL handshake has been sent, or that a CRC error has been
detected in a OUT isochronous endpoint.
Shall be cleared by software. Setting by software has no effect.

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• 0 - TXINI - Transmitter Ready Interrupt Flag
Set by hardware to signal that the current bank is free and can be filled. An interrupt (EPINTx) is
triggered (if enabled).
Shall be cleared by software to handshake the interrupt. Setting by software has no effect.
This bit is inactive (cleared) if the endpoint is an OUT endpoint.

Bit

7

6

5

4

3

2

1

FLERRENAKINE-NAKOUTERXSTPE

RXOUTESTALLEDE

TXINE

Read/Wri R/W
te

R/W

R

R/W

R/W

R/W

R/W

R/W

Initial
Value

0

0

0

0

0

0

0

0

0
UEIENX• 7 - FLERRE - Flow Error Interrupt Enable Flag
Set to enable an endpoint interrupt (EPINTx) when OVERFI or UNDERFI are sent.
Clear to disable an endpoint interrupt (EPINTx) when OVERFI or UNDERFI are sent.

• 6 - NAKINE - NAK IN Interrupt Enable Bit
Set to enable an endpoint interrupt (EPINTx) when NAKINI is set.
Clear to disable an endpoint interrupt (EPINTx) when NAKINI is set.

• 5 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 4 - NAKOUTE - NAK OUT Interrupt Enable Bit
Set to enable an endpoint interrupt (EPINTx) when NAKOUTI is set.
Clear to disable an endpoint interrupt (EPINTx) when NAKOUTI is set.

• 3 - RXSTPE - Received SETUP Interrupt Enable Flag
Set to enable an endpoint interrupt (EPINTx) when RXSTPI is sent.
Clear to disable an endpoint interrupt (EPINTx) when RXSTPI is sent.

• 2 - RXOUTE - Received OUT Data Interrupt Enable Flag
Set to enable an endpoint interrupt (EPINTx) when RXOUTI is sent.
Clear to disable an endpoint interrupt (EPINTx) when RXOUTI is sent.

• 1 - STALLEDE - Stalled Interrupt Enable Flag
Set to enable an endpoint interrupt (EPINTx) when STALLEDI is sent.
Clear to disable an endpoint interrupt (EPINTx) when STALLEDI is sent.

• 0 - TXINE - Transmitter Ready Interrupt Enable Flag
Set to enable an endpoint interrupt (EPINTx) when TXINI is sent.
Clear to disable an endpoint interrupt (EPINTx) when TXINI is sent.

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Bit

7

6

5

4

3

2

1

DAT D7DAT D6DAT D5DAT D4DAT D3DAT D2DAT D1DAT D0

Read/Wri R/W
te

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial
Value

0

0

0

0

0

0

0

0

0
UEDATX

• 7-0 - DAT7:0 -Data Bits
Set by the software to read/write a byte from/to the endpoint FIFO selected by EPNUM.

Bit

7

6

5

4

3

2

1

BYCT D7

BYCT D6

BYCT D5BYCT D4BYCT D3

BYCT D2

BYCT D1

BYCT D0

UEBCLX

Read/Wri R
te

R

R

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0

0

• 7-0 - BYCT7:0 - Byte Count Bits
Set by the hardware. BYCT7:0 is:- (for IN endpoint) increased after each writing into the endpoint and decremented after eachbyte sent,- (for OUT endpoint) increased after each byte sent by the host, and decremented after eachbyte read by the software.

Bit

7

6

5

4

3

2

1

0

-

-

-

EPINT D4EPINT D3

EPINT D2EPINT D1EPINT D0

UEINT

Read/Wri R
te

R

R

R

R

R

R

R

R

Initial
Value

0

0

0

0

0

0

0

0

• 7-5 - Reserved
The value read from these bits is always 0. Do not set these bits.
• 4-0 - EPINT4:0 - Endpoint Interrupts Bits
Set by hardware when an interrupt is triggered by the UEINTX register and if the corresponding
endpoint interrupt enable bit is set.
Cleared by hardware when the interrupt source is served.

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21. PS/2
21.1

Characteristics
The PS/2 pad IO’s characteristics are:– support 5.5V (min: 4.5V, max: 5.5V)– open drain type– Output voltage level threshold, MCU driving low thru a 1kΩ pull-up: VOLmax = 0,7V
– fall time with 1kΩ pull-up and 500pF load: 250ns < Tfall < 1µs– internal 2.2kΩ to 10kΩ pull-up at Vcc (5V), controlled by firmware.
– High impedance output when disabled.

Figure 21-1. USB pad and PS/2 pad multiplexing

PS/2 Pad

D+ / SCK

D- / SDATA

USB Pad

Bit

7

6

5

4

3

2

1

-

-

-

-

-

-

-

0
PS2EN

Read/Write

R

R

R

R

R

R

R

R/W

Initial Value

0

0

0

0

0

0

0

0

PS2CON• Bit 7:1 – Reserved bits
Do not set these bits.
• Bit 0 – PS2EN : PS/2 Pad Enable
Set this bit to “1” to enable the PS/2 pad.
Set this bit to “0” to disable the PS/2 pad.
For more information about pad driving, see “USB/PS2 Software Output Enable register –UPOE” on page 194.

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The UPOE register described in this section allows to read or writes values on the pad. PS/2
protocol must be entirely handled by software.

Figure 21-2. PS/2 Pad description
note: pull-up between 2.2k and 10k

Vcc
Z

4.7kΩ

Z

4.7kΩ

SDATA
SCK

Table 21-1.

PS/2 DC parameters

SymbolParameter

Condition

Min.

Typ.

Max.

UVCC

PS/2 power supply

4.0V

4.5V

5.5V

VIL

Input Low Voltage

UVCC = 4.5V - 5.5V

VIH

Input High Voltage

UVCC = 4.5V - 5.5V

2.4V

RIH

Pull-up resistor

UVCC = 4.5V - 5.5V

4.4kΩ

0.7V
5.1kΩ

6.5kΩ

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Table 21-2.

PS/2 AC parameters

SymbolParameter

Condition

Min.

Typ.

Max.

Tfall_output

Fall time

UVCC = 4.5V - 5.5V
10% - 90%
Rload = 1kΩ, Cload = 500pF

330ns

375ns

450ns

TspikeSpike width filtering

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22. Analog Comparator
The Analog Comparator compares the input values on the positive pin AIN0 and negative pin
AIN1. When the voltage on the positive pin AIN0 is higher than the voltage on the negative pin
AIN1, the Analog Comparator output, ACO, is set. The comparator’s output can be set to trigger
the Timer/Counter1 Input Capture function. In addition, the comparator can trigger a separate
interrupt, exclusive to the Analog Comparator. The user can select Interrupt triggering on comparator output rise, fall or toggle. A block diagram of the comparator and its surrounding logic isshown in Figure 22-1. User can also replace by software the AIN0 input by the internal Bandgap
reference.

Figure 22-1. Analog Comparator Block Diagram(1)BANDGAPREFERENCE
ACBG

Notes:

22.0.1

1. Refer to Figure 1-1 on page 3 and Table 11-9 on page 79 for Analog Comparator pin
placement.

Analog Comparator Control and Status Register – ACSR
Bit

7

6

5

4

3

2

1

0

ACD

ACBG

ACO

ACI

ACIE

ACIC

ACIS1

ACIS0

Read/Write

R/W

R/W

R

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

N/A

0

0

0

0

0

ACSR

• Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit ischanged.
• Bit 6 – ACBG: Analog Comparator Bandgap SelectWhen this bit is set, a fixed bandgap reference voltage replaces the positive input to the Analog
Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog Comparator. See “Internal Voltage Reference” on page 52.
• Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The
synchronization introduces a delay of 1 - 2 clock cycles.

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• Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode definedby ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is set
and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
• Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog Comparator interrupt is activated. When written logic zero, the interrupt is disabled.
• Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter1 to be triggered by the Analog Comparator. The comparator output is in this case directly connected to the
input capture front-end logic, making the comparator utilize the noise canceler and edge selectfeatures of the Timer/Counter1 Input Capture interrupt. When written logic zero, no connection
between the Analog Comparator and the input capture function exists. To make the comparator
trigger the Timer/Counter1 Input Capture interrupt, the ICIE1 bit in the Timer Interrupt Mask
Register (TIMSK1) must be set.
• Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The
different settings are shown in Table 22-1.
Table 22-1.

ACIS1/ACIS0 Settings

ACIS1

ACIS0

Interrupt Mode

00Comparator Interrupt on Output Toggle.

0

1

Reserved

10Comparator Interrupt on Falling Output Edge.

1

1

Comparator Interrupt on Rising Output Edge.

When changing the ACIS1/ACIS0 bits, the Analog Comparator Interrupt must be disabled byclearing its Interrupt Enable bit in the ACSR Register. Otherwise an interrupt can occur when thebits are changed.

22.0.2

Digital Input Disable Register 1 – DIDR1
Bit

7

6

5

4

3

2

1

–

–

–

–

–

–

AIN1D

0
AIN0D

Read/Write

R

R

R

R

R

R

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

DIDR1

• Bit 1, 0 – AIN1D, AIN0D: AIN1, AIN0 Digital Input Disable
When this bit is written logic one, the digital input buffer on the AIN1/0 pin is disabled. The corresponding PIN Register bit will always read as zero when this bit is set. When an analog signal isapplied to the AIN1/0 pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer.

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23. Boot Loader Support – Read-While-Write Self-Programming
The Boot Loader Support provides a real Read-While-Write Self-Programming mechanism for
downloading and uploading program code by the MCU itself. This feature allows flexible application software updates controlled by the MCU using a Flash-resident Boot Loader program. The
Boot Loader program can use any available data interface and associated protocol to read code
and write (program) that code into the Flash memory, or read the code from the program memory. The program code within the Boot Loader section has the capability to write into the entire
Flash, including the Boot Loader memory. The Boot Loader can thus even modify itself, and it
can also erase itself from the code if the feature is not needed anymore. The size of the Boot
Loader memory is configurable with fuses and the Boot Loader has two separate sets of Boot
Lock bits which can be set independently. This gives the user a unique flexibility to select different levels of protection.

23.1

Boot Loader Features• Read-While-Write Self-Programming• Flexible Boot Memory Size
• High Security (Separate Boot Lock Bits for a Flexible Protection)• Separate Fuse to Select Reset Vector• Optimized Page(1) Size
• Code Efficient Algorithm• Efficient Read-Modify-Write Support
Note:

23.2

1. A page is a section in the Flash consisting of several bytes (see Table 25-11 on page 248)
used during programming. The page organization does not affect normal operation.

Application and Boot Loader Flash Sections
The Flash memory is organized in two main sections, the Application section and the Boot
Loader section (see Figure 23-2). The size of the different sections is configured by the
BOOTSZ Fuses as shown in Table 23-8 on page 239 and Figure 23-2. These two sections canhave different level of protection since they have different sets of Lock bits.

23.2.1

Application Section
The Application section is the section of the Flash that is used for storing the application code.
The protection level for the Application section can be selected by the application Boot Lock bits
(Boot Lock bits 0), see Table 23-2 on page 229. The Application section can never store any
Boot Loader code since the SPM instruction is disabled when executed from the Application
section.

23.2.2

BLS – Boot Loader Section
While the Application section is used for storing the application code, the The Boot Loader software must be located in the BLS since the SPM instruction can initiate a programming when
executing from the BLS only. The SPM instruction can access the entire Flash, including the
BLS itself. The protection level for the Boot Loader section can be selected by the Boot Loader
Lock bits (Boot Lock bits 1), see Table 23-3 on page 229.

23.3

Read-While-Write and No Read-While-Write Flash Sections
Whether the CPU supports Read-While-Write or if the CPU is halted during a Boot Loader software update is dependent on which address that is being programmed. In addition to the two
sections that are configurable by the BOOTSZ Fuses as described above, the Flash is also

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divided into two fixed sections, the Read-While-Write (RWW) section and the No Read-WhileWrite (NRWW) section. The limit between the RWW- and NRWW sections is given in Table 231 and Figure 23-1 on page 227. The main difference between the two sections is:• When erasing or writing a page located inside the RWW section, the NRWW section can beread during the operation.
• When erasing or writing a page located inside the NRWW section, the CPU is halted during
the entire operation.
Note that the user software can never read any code that is located inside the RWW section during a Boot Loader software operation. The syntax “Read-While-Write section” refers to which
section that is being programmed (erased or written), not which section that actually is being
read during a Boot Loader software update.

23.3.1RWW – Read-While-Write Section
If a Boot Loader software update is programming a page inside the RWW section, it is possible
to read code from the Flash, but only code that is located in the NRWW section. During an ongoing programming, the software must ensure that the RWW section never is being read. If theuser software is trying to read code that is located inside the RWW section (i.e., by load program
memory, call, or jump instructions or an interrupt) during programming, the software might end
up in an unknown state. To avoid this, the interrupts should either be disabled or moved to the
Boot Loader section. The Boot Loader section is always located in the NRWW section. The
RWW Section Busy bit (RWWSB) in the Store Program Memory Control and Status Register(SPMCSR) will be read as logical one as long as the RWW section is blocked for reading. Aftera programming is completed, the RWWSB must be cleared by software before reading code
located in the RWW section. See “Store Program Memory Control and Status Register –SPMCSR” on page 231. for details on how to clear RWWSB.

23.3.2NRWW – No Read-While-Write Section
The code located in the NRWW section can be read when the Boot Loader software is updatinga page in the RWW section. When the Boot Loader code updates the NRWW section, the CPU
is halted during the entire Page Erase or Page Write operation.
Table 23-1.

226

Read-While-Write Features

Which Section does the Z-pointerAddress During the Programming?

Which Section Can
be Read During
Programming?

Is the CPU
Halted?

Read-While-Write
Supported?

RWW Section

NRWW Section

No

Yes

NRWW Section

None

Yes

No

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Figure 23-1. Read-While-Write vs. No Read-While-Write

Read-While-Write(RWW) Section

Z-pointer
Addresses RWW
SectionZ-pointer
Addresses NRWW
SectionNo Read-While-Write(NRWW) Section

CPU is Halted
During the Operation
Code Located in
NRWW Section
Can be Read During
the Operation

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Figure 23-2. Memory Sections
Program Memory
BOOTSZ = '10'

Program Memory
BOOTSZ = '11'0x0000

No Read-While-Write Section

Read-While-Write Section

Application Flash Section

End RWW
Start NRWW
Application Flash Section

Boot Loader Flash Section

End Application
Start Boot Loader
Flashend

No Read-While-Write Section

Read-While-Write Section

0x0000Program Memory
BOOTSZ = '01'

Application Flash Section

End RWW
Start NRWW
Application Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend
Program Memory
BOOTSZ = '00'

23.4

Read-While-Write Section

Application Flash Section

No Read-While-Write Section

Note:

0x0000End RWW
Start NRWW
Application Flash Section
End Application
Start Boot Loader
Boot Loader Flash Section
Flashend

No Read-While-Write Section

Read-While-Write Section

0x0000Application Flash Section

End RWW, End Application
Start NRWW, Start Boot Loader

Boot Loader Flash Section

Flashend

1. The parameters in the figure above are given in Table 23-8 on page 239.

Boot Loader Lock Bits
If no Boot Loader capability is needed, the entire Flash is available for application code. The
Boot Loader has two separate sets of Boot Lock bits which can be set independently. This gives
the user a unique flexibility to select different levels of protection.
The user can select:• To protect the entire Flash from a software update by the MCU.
• To protect only the Boot Loader Flash section from a software update by the MCU.
• To protect only the Application Flash section from a software update by the MCU.
• Allow software update in the entire Flash.
See Table 23-2 and Table 23-3 for further details. The Boot Lock bits can be set in software andin Serial or Parallel Programming mode, but they can be cleared by a Chip Erase command
only. The general Write Lock (Lock Bit mode 2) does not control the programming of the Flashmemory by SPM instruction. Similarly, the general Read/Write Lock (Lock Bit mode 1) does notcontrol reading nor writing by (E)LPM/SPM, if it is attempted.

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Table 23-2.
BLB0 Mode

BLB02

BLB01

1

1

1

No restrictions for SPM or (E)LPM accessing the Application
section.

2

1

0

SPM is not allowed to write to the Application section.

0

SPM is not allowed to write to the Application section, and(E)LPM executing from the Boot Loader section is not allowed
to read from the Application section. If Interrupt Vectors areplaced in the Boot Loader section, interrupts are disabled while
executing from the Application section.

1(E)LPM executing from the Boot Loader section is not allowed
to read from the Application section. If Interrupt Vectors areplaced in the Boot Loader section, interrupts are disabled while
executing from the Application section.

3

4
Note:

0

0

Protection

1. “1” means unprogrammed, “0” means programmed

Table 23-3.

Boot Lock Bit1 Protection Modes (Boot Loader Section)(1)

BLB1 Mode

BLB12

BLB11

1

1

1

No restrictions for SPM or (E)LPM accessing the Boot Loader
section.

2

1

0

SPM is not allowed to write to the Boot Loader section.

0

SPM is not allowed to write to the Boot Loader section, and(E)LPM executing from the Application section is not allowed toread from the Boot Loader section. If Interrupt Vectors areplaced in the Application section, interrupts are disabled while
executing from the Boot Loader section.

1(E)LPM executing from the Application section is not allowed toread from the Boot Loader section. If Interrupt Vectors areplaced in the Application section, interrupts are disabled while
executing from the Boot Loader section.

3

4
Note:

23.5

Boot Lock Bit0 Protection Modes (Application Section)(1)00Protection

1. “1” means unprogrammed, “0” means programmed

Entering the Boot Loader Program
The bootloader can be executed with three different conditions:23.5.1

Regular application conditions.
A jump or call from the application program. This may be initiated by a trigger such as a command received via USART, or SPI interface.

23.5.2

Boot Reset Fuse
The Boot Reset Fuse (BOOTRST) can be programmed so that the Reset Vector is pointing to
the Boot Flash start address after a reset. In this case, the Boot Loader is started after a reset.
After the application code is loaded, the program can start executing the application code. Notethat the fuses cannot be changed by the MCU itself. This means that once the Boot Reset Fuse

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is programmed, the Reset Vector will always point to the Boot Loader Reset and the fuse canonly be changed through the serial or parallel programming interface.

Table 23-4.
BOOTRST

Note:

23.5.3

Boot Reset Fuse(1)Reset Address

1

Reset Vector = Application Reset (address 0x0000)

0Reset Vector = Boot Loader Reset (see Table 23-8 on page 239)

1. “1” means unprogrammed, “0” means programmed

External Hardware conditions
The Hardware Boot Enable Fuse (HWBE) can be programmed (See Table 23-5) so that upon
special hardware conditions under reset, the bootloader execution is forced after reset.
Table 23-5.
HWBE

Note:

Hardware Boot Enable Fuse(1)Reset Address

1

PD7/HWB pin can not be used to force Boot Loader execution after reset

0

PD7/HWB pin is used during reset to force bootloader execution after reset

1. “1” means unprogrammed, “0” means programmed

When the HWBE fuse is enable the PD7/HWB pin is configured as input during reset and sampled during reset rising edge. When PD7/HWB pin is ‘0’ during reset rising edge, the reset vector
will be set as the Boot Loader Reset address and the Boot Loader will be executed (See Figures23-3).

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Figure 23-3. Boot Process Description
RESET

tHHRH

tSHRH
PD7/HWBHWBE ?

Ext. Hardware
Conditions ?

BOOTRST ?

Reset Vector = Application Reset

23.5.4

Reset Vector =Boot Lhoader ResetStore Program Memory Control and Status Register – SPMCSR
The Store Program Memory Control and Status Register contains the control bits needed to control the Boot Loader operations.
Bit

7

6

5

4

3

2

1

0

SPMIE

RWWSB

SIGRD

RWWSREBLBSET

PGWRT

PGERS

SPMEN

Read/Write

R/W

R

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

SPMCSR• Bit 7 – SPMIE: SPM Interrupt Enable
When the SPMIE bit is written to one, and the I-bit in the Status Register is set (one), the SPM
ready interrupt will be enabled. The SPM ready Interrupt will be executed as long as the SPMEN
bit in the SPMCSR Register is cleared.
• Bit 6 – RWWSB: Read-While-Write Section Busy
When a Self-Programming (Page Erase or Page Write) operation to the RWW section is initiated, the RWWSB will be set (one) by hardware. When the RWWSB bit is set, the RWW section
cannot be accessed. The RWWSB bit will be cleared if the RWWSRE bit is written to one after a
Self-Programming operation is completed. Alternatively the RWWSB bit will automatically becleared if a page load operation is initiated.
• Bit 5 – SIGRD: Signature Row Read
If this bit is written to one at the same time as SPMEN, the next LPM instruction within threeclock cycles will read a byte from the signature row into the destination register. see “Reading
the Signature Row from Software” on page 236 for details. An SPM instruction within four cycles

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after SIGRD and SPMEN are set will have no effect. This operation is reserved for future use
and should not be used.

• Bit 4 – RWWSRE: Read-While-Write Section Read Enable
When programming (Page Erase or Page Write) to the RWW section, the RWW section isblocked for reading (the RWWSB will be set by hardware). To re-enable the RWW section, theuser software must wait until the programming is completed (SPMEN will be cleared). Then, if
the RWWSRE bit is written to one at the same time as SPMEN, the next SPM instruction withinfour clock cycles re-enables the RWW section. The RWW section cannot be re-enabled while
the Flash is busy with a Page Erase or a Page Write (SPMEN is set). If the RWWSRE bit is written while the Flash is being loaded, the Flash load operation will abort and the data loaded will
be lost.
• Bit 3 – BLBSET: Boot Lock Bit Set
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles sets Boot Lock bits, according to the data in R0. The data in R1 and the address in the Zpointer are ignored. The BLBSET bit will automatically be cleared upon completion of the Lockbit set, or if no SPM instruction is executed within four clock cycles.
An (E)LPM instruction within three cycles after BLBSET and SPMEN are set in the SPMCSR
Register, will read either the Lock bits or the Fuse bits (depending on Z0 in the Z-pointer) into thedestination register. See “Reading the Fuse and Lock Bits from Software” on page 235 fordetails.

• Bit 2 – PGWRT: Page Write
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Write, with the data stored in the temporary buffer. The page address istaken from the high part of the Z-pointer. The data in R1 and R0 are ignored. The PGWRT bit
will auto-clear upon completion of a Page Write, or if no SPM instruction is executed within four
clock cycles. The CPU is halted during the entire Page Write operation if the NRWW section isaddressed.
• Bit 1 – PGERS: Page Erase
If this bit is written to one at the same time as SPMEN, the next SPM instruction within four clock
cycles executes Page Erase. The page address is taken from the high part of the Z-pointer. The
data in R1 and R0 are ignored. The PGERS bit will auto-clear upon completion of a Page Erase,
or if no SPM instruction is executed within four clock cycles. The CPU is halted during the entire
Page Write operation if the NRWW section is addressed.
• Bit 0 – SPMEN: Store Program Memory Enable
This bit enables the SPM instruction for the next four clock cycles. If written to one together witheither RWWSRE, BLBSET, PGWRT’ or PGERS, the following SPM instruction will have a special meaning, see description above. If only SPMEN is written, the following SPM instruction willstore the value in R1:R0 in the temporary page buffer addressed by the Z-pointer. The LSB ofthe Z-pointer is ignored. The SPMEN bit will auto-clear upon completion of an SPM instruction,or if no SPM instruction is executed within four clock cycles. During Page Erase and Page Write,
the SPMEN bit remains high until the operation is completed.
Writing any other combination than “10001”, “01001”, “00101”, “00011” or “00001” in the lower
five bits will have no effect.

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Note:

23.6

Only one SPM instruction should be active at any time.

Addressing the Flash During Self-Programming
The Z-pointer is used to address the SPM commands. The Z pointer consists of the Z-registers
ZL and ZH in the register file. The number of bits actually used is implementation dependent.
Since the Flash is organized in pages (see Table 25-11 on page 248), the Program Counter canbe treated as having two different sections. One section, consisting of the least significant bits, isaddressing the words within a page, while the most significant bits are addressing the pages.
This is shown in Figure 23-4. Note that the Page Erase and Page Write operations are
addressed independently. Therefore it is of major importance that the Boot Loader software
addresses the same page in both the Page Erase and Page Write operation. Once a programming operation is initiated, the address is latched and the Z-pointer can be used for otheroperations.
The (E)LPM instruction use the Z-pointer to store the address. Since this instruction addresses
the Flash byte-by-byte, also bit Z0 of the Z-pointer is used.

Figure 23-4. Addressing the Flash During SPM(1)BIT

15ZPCMSBZPAGEMSB

Z - REGISTER

1 0
0

PCMSB
PROGRAM
COUNTERPAGEMSB
PCPAGEPCWORD

PAGE ADDRESSWITHIN THE FLASHPROGRAM MEMORY
PAGE

WORD ADDRESSWITHIN A PAGE
PAGE
INSTRUCTION WORD

PCWORD[PAGEMSB:0]:
00
01
02

PAGEEND

Note:

23.7

1. The different variables used in Figure 23-4 are listed in Table 23-10 on page 240.

Self-Programming the FlashThe program memory is updated in a page by page fashion. Before programming a page withthe data stored in the temporary page buffer, the page must be erased. The temporary page buffer is filled one word at a time using SPM and the buffer can be filled either before the Page
Erase command or between a Page Erase and a Page Write operation:
Alternative 1, fill the buffer before a Page Erase• Fill temporary page buffer

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• Perform a Page Erase• Perform a Page Write
Alternative 2, fill the buffer after Page Erase• Perform a Page Erase• Fill temporary page buffer• Perform a Page Write
If only a part of the page needs to be changed, the rest of the page must be stored (for example
in the temporary page buffer) before the erase, and then be rewritten. When using alternative 1,
the Boot Loader provides an effective Read-Modify-Write feature which allows the user software
to first read the page, do the necessary changes, and then write back the modified data. If alternative 2 is used, it is not possible to read the old data while loading since the page is alreadyerased. The temporary page buffer can be accessed in a random sequence. It is essential thatthe page address used in both the Page Erase and Page Write operation is addressing thesame page. See “Simple Assembly Code Example for a Boot Loader” on page 237 for an
assembly code example.

23.7.1

Performing Page Erase by SPM
To execute Page Erase, set up the address in the Z-pointer, write “X0000011” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE in the Z-register. Other bits in the Z-pointer willbe ignored during this operation.
• Page Erase to the RWW section: The NRWW section can be read during the Page Erase.
• Page Erase to the NRWW section: The CPU is halted during the operation.

23.7.2Filling the Temporary Buffer (Page Loading)To write an instruction word, set up the address in the Z-pointer and data in R1:R0, write“00000001” to SPMCSR and execute SPM within four clock cycles after writing SPMCSR. The
content of PCWORD in the Z-register is used to address the data in the temporary buffer. The
temporary buffer will auto-erase after a Page Write operation or by writing the RWWSRE bit in
SPMCSR. It is also erased after a system reset. Note that it is not possible to write more than
one time to each address without erasing the temporary buffer.
If the EEPROM is written in the middle of an SPM Page Load operation, all data loaded will be
lost.

23.7.3

Performing a Page Write
To execute Page Write, set up the address in the Z-pointer, write “X0000101” to SPMCSR and
execute SPM within four clock cycles after writing SPMCSR. The data in R1 and R0 is ignored.
The page address must be written to PCPAGE. Other bits in the Z-pointer must be written tozero during this operation.
• Page Write to the RWW section: The NRWW section can be read during the Page Write.
• Page Write to the NRWW section: The CPU is halted during the operation.

23.7.4

234

Using the SPM Interrupt
If the SPM interrupt is enabled, the SPM interrupt will generate a constant interrupt when the
SPMEN bit in SPMCSR is cleared. This means that the interrupt can be used instead of polling
the SPMCSR Register in software. When using the SPM interrupt, the Interrupt Vectors should

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be moved to the BLS section to avoid that an interrupt is accessing the RWW section when it isblocked for reading. How to move the interrupts is described in “Interrupts” on page 63.

23.7.5

Consideration While Updating BLS
Special care must be taken if the user allows the Boot Loader section to be updated by leaving
Boot Lock bit11 unprogrammed. An accidental write to the Boot Loader itself can corrupt theentire Boot Loader, and further software updates might be impossible. If it is not necessary tochange the Boot Loader software itself, it is recommended to program the Boot Lock bit11 toprotect the Boot Loader software from any internal software changes.

23.7.6

Prevent Reading the RWW Section During Self-Programming
During Self-Programming (either Page Erase or Page Write), the RWW section is always
blocked for reading. The user software itself must prevent that this section is addressed during
the self programming operation. The RWWSB in the SPMCSR will be set as long as the RWW
section is busy. During Self-Programming the Interrupt Vector table should be moved to the BLS
as described in “Interrupts” on page 63, or the interrupts must be disabled. Before addressing
the RWW section after the programming is completed, the user software must clear the
RWWSB by writing the RWWSRE. See “Simple Assembly Code Example for a Boot Loader” onpage 237 for an example.

23.7.7

Setting the Boot Loader Lock Bits by SPM
To set the Boot Loader Lock bits, write the desired data to R0, write “X0001001” to SPMCSR
and execute SPM within four clock cycles after writing SPMCSR. The only accessible Lock bits
are the Boot Lock bits that may prevent the Application and Boot Loader section from any software update by the MCU.
Bit

7

6

5

4

3

2

1

0

R0

1

1

BLB12

BLB11

BLB02

BLB01

1

1

See Table 23-2 and Table 23-3 for how the different settings of the Boot Loader bits affect theFlash access.
If bits 5..2 in R0 are cleared (zero), the corresponding Boot Lock bit will be programmed if an
SPM instruction is executed within four cycles after BLBSET and SPMEN are set in SPMCSR.
The Z-pointer is don’t care during this operation, but for future compatibility it is recommended toload the Z-pointer with 0x0001 (same as used for reading the lOck bits). For future compatibility it
is also recommended to set bits 7, 6, 1, and 0 in R0 to “1” when writing the Lock bits. When programming the Lock bits the entire Flash can be read during the operation.

23.7.8EEPROM Write Prevents Writing to SPMCSR
Note that an EEPROM write operation will block all software programming to Flash. Reading theFuses and Lock bits from software will also be prevented during the EEPROM write operation. It
is recommended that the user checks the status bit (EEPE) in the EECR Register and verifies
that the bit is cleared before writing to the SPMCSR Register.

23.7.9Reading the Fuse and Lock Bits from Software
It is possible to read both the Fuse and Lock bits from software. To read the Lock bits, load theZ-pointer with 0x0001 and set the BLBSET and SPMEN bits in SPMCSR. When an (E)LPM
instruction is executed within three CPU cycles after the BLBSET and SPMEN bits are set in
SPMCSR, the value of the Lock bits will be loaded in the destination register. The BLBSET and
SPMEN bits will auto-clear upon completion of reading the Lock bits or if no (E)LPM instruction

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is executed within three CPU cycles or no SPM instruction is executed within four CPU cycles.
When BLBSET and SPMEN are cleared, (E)LPM will work as described in the Instruction set
Manual.
Bit

7

6

5

4

3

2

1

0

Rd

–

–

BLB12

BLB11

BLB02

BLB01

LB2

LB1

The algorithm for reading the Fuse Low byte is similar to the one described above for reading
the Lock bits. To read the Fuse Low byte, load the Z-pointer with 0x0000 and set the BLBSET
and SPMEN bits in SPMCSR. When an (E)LPM instruction is executed within three cycles after
the BLBSET and SPMEN bits are set in the SPMCSR, the value of the Fuse Low byte (FLB) will
be loaded in the destination register as shown below. Refer to Table 25-5 on page 245 for a
detailed description and mapping of the Fuse Low byte.
Bit

7

6

5

4

3

2

1

0

Rd

FLB7

FLB6

FLB5

FLB4

FLB3

FLB2

FLB1

FLB0

Similarly, when reading the Fuse High byte, load 0x0003 in the Z-pointer. When an (E)LPM
instruction is executed within three cycles after the BLBSET and SPMEN bits are set in the
SPMCSR, the value of the Fuse High byte (FHB) will be loaded in the destination register asshown below. Refer to Table 25-4 on page 245 for detailed description and mapping of the Fuse
High byte.
Bit

7

6

5

4

3

2

1

0

Rd

FHB7

FHB6

FHB5

FHB4

FHB3

FHB2

FHB1

FHB0

When reading the Extended Fuse byte, load 0x0002 in the Z-pointer. When an (E)LPM instruction is executed within three cycles after the BLBSET and SPMEN bits are set in the SPMCSR,
the value of the Extended Fuse byte (EFB) will be loaded in the destination register as shown
below. Refer to Table 25-3 on page 244 for detailed description and mapping of the Extended
Fuse byte.
Bit

7

6

5

4

3

2

1

0

Rd

–

–

–

–

–

EFB2

EFB1

EFB0

Fuse and Lock bits that are programmed, will be read as zero. Fuse and Lock bits that are
unprogrammed, will be read as one.

23.7.10

Reading the Signature Row from Software
To read the Signature Row from software, load the Z-pointer with the signature byte address
given in Table 23-6 on page 236 and set the SIGRD and SPMEN bits in SPMCSR. When an
LPM instruction is executed within three CPU cycles after the SIGRD and SPMEN bits are set in
SPMCSR, the signature byte value will be loaded in the destination register. The SIGRD and
SPMEN bits will auto-clear upon completion of reading the Signature Row Lock bits or if no LPM
instruction is executed within three CPU cycles. When SIGRD and SPMEN are cleared, LPM will
work as described in the Instruction set Manual.
Table 23-6.

236

Signature Row Addressing

Signature Byte

Z-Pointer Address

Device Signature Byte 10x0000Device Signature Byte 20x0002

Device Signature Byte 30x0004

RC Oscillator Calibration Byte

0x0001

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Note:

23.7.11

All other addresses are reserved for future use.

Preventing Flash Corruption
During periods of low VCC, the Flash program can be corrupted because the supply voltage is
too low for the CPU and the Flash to operate properly. These issues are the same as for board
level systems using the Flash, and the same design solutions should be applied.
A Flash program corruption can be caused by two situations when the voltage is too low. First, aregular write sequence to the Flash requires a minimum voltage to operate correctly. Secondly,
the CPU itself can execute instructions incorrectly, if the supply voltage for executing instructions
is too low.
Flash corruption can easily be avoided by following these design recommendations (one issufficient):
1. If there is no need for a Boot Loader update in the system, program the Boot Loader
Lock bits to prevent any Boot Loader software updates.
2. Keep the AVR RESET active (low) during periods of insufficient power supply voltage.
This can be done by enabling the internal Brown-out Detector (BOD) if the operating
voltage matches the detection level. If not, an external low VCC reset protection circuit
can be used. If a reset occurs while a write operation is in progress, the write operation
will be completed provided that the power supply voltage is sufficient.
3. Keep the AVR core in Power-down sleep mode during periods of low VCC. This will prevent the CPU from attempting to decode and execute instructions, effectively protecting
the SPMCSR Register and thus the Flash from unintentional writes.

23.7.12Programming Time for Flash when Using SPM
The calibrated RC Oscillator is used to time Flash accesses. Table 23-7 shows the typical programming time for Flash accesses from the CPU.
Table 23-7.

23.7.13

SPM Programming Time
SymbolMin Programming TimeMax Programming Time

Flash write (Page Erase, Page Write, andwrite Lock bits by SPM)

3.7 ms

4.5 msSimple Assembly Code Example for a Boot Loader;-the routine writes one page of data from RAM to Flash; the first data location in RAM is pointed to by the Y pointer; the first data location in Flash is pointed to by the Z-pointer;-error handling is not included;-the routine must be placed inside the Boot space; (at least the Do_spm sub routine). Only code inside NRWW section can; be read during Self-Programming (Page Erase and Page Write).
;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24),; loophi (r25), spmcrval (r20); storing and restoring of registers is not included in the routine; register usage can be optimized at the expense of code size;-It is assumed that either the interrupt table is moved to the Boot
; loader section or that the interrupts are disabled.
.equ PAGESIZEB = PAGESIZE*2;PAGESIZEB is page size in BYTES, not words.org SMALLBOOTSTART
Write_page:; Page Eraseldi spmcrval, (1<<PGERS) | (1<<SPMEN)

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call Do_spm; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm; transfer data from RAM to Flash page buffer
ldi looplo, low(PAGESIZEB);init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
Wrloop:ld
r0, Y+
ld
r1, Y+
ldi spmcrval, (1<<SPMEN)
call Do_spm
adiw ZH:ZL, 2
sbiw loophi:looplo, 2;use subi for PAGESIZEB<=256
brne Wrloop; execute Page Write
subi ZL, low(PAGESIZEB);restore pointersbci ZH, high(PAGESIZEB);not required for PAGESIZEB<=256
ldi spmcrval, (1<<PGWRT) | (1<<SPMEN)
call Do_spm; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm; read back and check, optional
ldi looplo, low(PAGESIZEB);init loop variable
ldi loophi, high(PAGESIZEB) ;not required for PAGESIZEB<=256
subi YL, low(PAGESIZEB);restore pointersbci YH, high(PAGESIZEB)
Rdloop:elpm r0, Z+
ld
r1, Y+
cpse r0, r1
jmp Error
sbiw loophi:looplo, 1;use subi for PAGESIZEB<=256
brne Rdloop; return to RWW section; verify that RWW section is safe to read
Return:in
temp1, SPMCSR
sbrs temp1, RWWSB; If RWWSB is set, the RWW section is not ready yet
ret; re-enable the RWW section
ldi spmcrval, (1<<RWWSRE) | (1<<SPMEN)
call Do_spm
rjmp Return
Do_spm:; check for previous SPM complete
Wait_spm:
temp1, SPMCSR
insbrc temp1, SPMEN
rjmp Wait_spm; input: spmcrval determines SPM action

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AT90USB82/162; disable interrupts if enabled, store statusin
temp2, SREGcli
; check that no EEPROM write access is present
Wait_ee:sbic EECR, EEPE
rjmp Wait_ee; SPM timed sequence
out SPMCSR, spmcrval
spm; restore SREG (to enable interrupts if originally enabled)out SREG, temp2
ret

AT90USB82/162 Boot Loader Parameters
In Table 23-8 through Table 23-10, the parameters used in the description of the Self-Programming are given.

Boot Reset
Address (Start Boot
Loader Section)

End Application
SectionBoot Loader
Flash Section(byte address)

1

1

512 bytes

40x0000 0x3DFF

0x3E00 0x3FFF

0x3DFF0x3E001

01024 bytes

80x0000 0x3BFF

0x3C00 0x3FFF

0x3BFF

0x3C00012048 bytes

160x0000 0x37FF

0x3800 0x3FFF

0x37FF0x3800004096 bytes

32

0x0000 0x2FFF

0x3000 0x3FFF

0x2FFF0x30001

1

512 bytes

40x0000 0x1DFF

0x1E00 0x1FFF

0x1DFF0x1E001

01024 bytes

80x0000 0x1BFF

0x1C00 0x1FFF

0x1BFF

0x1C00012048 bytes

160x0000 0x17FF

0x1800 0x1FFF

0x17FF0x1800004096 bytes

32

0x0000 0x0FFF

0x1000 0x1FFF

0x0FFF

0x1000Pages

BOOTSZ0

8Kb

BOOTSZ1

DEVICE
16K
b

Application
Flash Section(byte address)

Boot Size Configuration() (16k)

Table 23-8.

Boot Size (in bytes)

23.7.14(Page size = 64 words = 128 bytes)

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The different BOOTSZ Fuse configurations are shown in Figure 23-2.

Table 23-9.

Read-While-Write Limit(1)DeviceSection

16K
8K
Note:

Pages

Address

Read-While-Write section (RWW)

960x0000 - 0x2FFF

No Read-While-Write section (NRWW)

32

0x3000 - 0x3FFF

Read-While-Write section (RWW)

320x0000 - 0x0FFF

No Read-While-Write section (NRWW)

32

0x1000 - 0x1FFF

1. For details about these two section, see “NRWW – No Read-While-Write Section” on page
226 and “RWW – Read-While-Write Section” on page 226.

Table 23-10. Explanation of different variables used in Figure 23-4 and the mapping to the ZpointerCorresponding
Z-value

Variable

Description(1)

PCMSB

12

Most significant bit in the Program Counter. (The
Program Counter is 13 bits PC[12:0])

PAGEMSB

5

Most significant bit which is used to address thewords within one page (64 words in a pagerequires six bits PC [5:0]).

ZPCMSBZ13

Bit in Z-pointer that is mapped to PCMSB.
Because Z0 is not used, the ZPCMSB equals
PCMSB + 1.

ZPAGEMSB

Z6

Bit in Z-pointer that is mapped to PCMSB.
Because Z0 is not used, the ZPAGEMSB equals
PAGEMSB + 1.

PCPAGEPC[12:6]

Z13:Z7

Program Counter page address: Page select,
for Page Erase and Page Write

PCWORD

PC[5:0]

Z6:Z1

Program Counter word address: Word select,
for filling temporary buffer (must be zero during
Page Write operation)

Note:

1. Z0: should be zero for all SPM commands, byte select for the (E)LPM instruction.

See “Addressing the Flash During Self-Programming” on page 233 for details about the use of
Z-pointer during Self-Programming.

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AT90USB82/162
24. debugWIRE On-chip Debug System
24.1

Features24.2

Overview• Complete Program Flow Control• Emulates All On-chip Functions, Both Digital and Analog, except RESET Pin• Real-time Operation• Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs)• Unlimited Number of Program Break Points (Using Software Break Points)• Non-intrusive Operation• Electrical Characteristics Identical to Real Device• Automatic Configuration System• High-Speed Operation• Programming of Non-volatile Memories

The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the
program flow, execute AVR instructions in the CPU and to program the different non-volatilememories.

24.3

Physical Interface
When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed,the debugWIRE system within the target device is activated. The RESET port pin is configured
as a wire-AND (open-drain) bi-directional I/O pin and becomes the communication gateway
between target and emulator.

Figure 24-1. The debugWIRE Setup

2.7 - 5.5

(See Note)

VCC

dW

dW(RESET)

GND

Figure 24-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator
connector. The system clock is not affected by debugWIRE and will always be the clock source
selected by the CKSEL Fuses.

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When designing a system where debugWIRE will be used, the following observations must be
made for correct operation:• Connecting the RESET pin directly to VCC will not work.
• Any capacitors (or additionnal circuitry) connected to the RESET pin must be disconnected
when using debugWire.
• All external reset sources must be disconnected.
Note:

24.4

some releases of JTAG Ice mkII firmware may require a pull-up resistor with a value between 8
and 14 kOhms when operating at 5V.

Software Break Points
debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a
Break Point in AVR Studio® will insert a BREAK instruction in the Program memory. The instruction replaced by the BREAK instruction will be stored. When program execution is continued, thestored instruction will be executed before continuing from the Program memory. A break can beinserted manually by putting the BREAK instruction in the program.
The Flash must be re-programmed each time a Break Point is changed. This is automaticallyhandled by AVR Studio through the debugWIRE interface. The use of Break Points will therefore
reduce the Flash Data retention. Devices used for debugging purposes should not be shipped to
end customers.

24.5

Limitations of debugWIRE
The debugWIRE communication pin (dW) is physically located on the same pin as External
Reset (RESET). An External Reset source is therefore not supported when the debugWIRE isenabled.
The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,
when the program in the CPU is running. When the CPU is stopped, care must be taken whileaccessing some of the I/O Registers via the debugger (AVR Studio).
A programmed DWEN Fuse enables some parts of the clock system to be running in all sleep
modes. This will increase the power consumption while in sleep. Thus, the DWEN Fuse should
be disabled when debugWire is not used.

24.6

debugWIRE Related Register in I/O Memory
The following section describes the registers used with the debugWire.

24.6.1debugWire Data Register – DWDR
Bit

7

6

5

4

3

2

1

0

DWDR[7:0]

DWDR

Read/Write

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

Initial Value

0

0

0

0

0

0

0

0

The DWDR Register provides a communication channel from the running program in the MCU
to the debugger. This register is only accessible by the debugWIRE and can therefore not be
used as a general purpose register in the normal operations.

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AT90USB82/162
25. Memory Programming
25.1

Program And Data Memory Lock Bits
The AT90USB82/162 provides six Lock bits which can be left unprogrammed (“1”) or can be programmed (“0”) to obtain the additional features listed in Table 25-2. The Lock bits can only beerased to “1” with the Chip Erase command.

Table 25-1.

Lock Bit Byte(1)Lock Bit Byte

Description

Default Value

7–

1 (unprogrammed)

6–

1 (unprogrammed)

BLB12

5

Boot Lock bit

1 (unprogrammed)

BLB11

4

Boot Lock bit

0 (programmed)

BLB02

3

Boot Lock bit

1 (unprogrammed)

BLB01

2

Boot Lock bit

1 (unprogrammed)

LB2

1

Lock bit0 (programmed)

LB1

0

Lock bit0 (programmed)

Note:

1. “1” means unprogrammed, “0” means programmed

Table 25-2.

Bit NoLock Bit Protection Modes(1)(2)

Memory Lock Bits

Protection TypeLB Mode

LB2

LB1

1

1

1

No memory lock features enabled.

2

1

0

Further programming of the Flash and EEPROM is disabled in
Parallel and Serial Programming mode. The Fuse bits arelocked in both Serial and Parallel Programming mode.(1)Further programming and verification of the Flash and
EEPROM is disabled in Parallel and Serial Programming mode.
The Boot Lock bits and Fuse bits are locked in both Serial andParallel Programming mode.(1)

3

0

0

BLB0 Mode

BLB02

BLB01

1

1

1

No restrictions for SPM or (E)LPM accessing the Application
section.

2

1

0

SPM is not allowed to write to the Application section.

0

SPM is not allowed to write to the Application section, and(E)LPM executing from the Boot Loader section is not allowed
to read from the Application section. If Interrupt Vectors areplaced in the Boot Loader section, interrupts are disabled while
executing from the Application section.

1(E)LPM executing from the Boot Loader section is not allowed
to read from the Application section. If Interrupt Vectors areplaced in the Boot Loader section, interrupts are disabled while
executing from the Application section.

3

4

0

0

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Lock Bit Protection Modes(1)(2) (Continued)

Table 25-2.

Memory Lock Bits

Protection Type

BLB1 Mode

BLB12

BLB11

1

1

1

No restrictions for SPM or (E)LPM accessing the Boot Loader
section.

2

1

0

SPM is not allowed to write to the Boot Loader section.

0

SPM is not allowed to write to the Boot Loader section, and(E)LPM executing from the Application section is not allowed toread from the Boot Loader section. If Interrupt Vectors areplaced in the Application section, interrupts are disabled while
executing from the Boot Loader section.

1(E)LPM executing from the Application section is not allowed toread from the Boot Loader section. If Interrupt Vectors areplaced in the Application section, interrupts are disabled while
executing from the Boot Loader section.

3

0

4
Notes:

0

1. Program the Fuse bits and Boot Lock bits before programming the LB1 and LB2.
2. “1” means unprogrammed, “0” means programmed

25.2

Fuse Bits
The AT90USB82/162 has four Fuse bytes. Table 25-3 - Table 25-5 describe briefly the functionality of all the fuses and how they are mapped into the Fuse bytes. Note that the fuses are readas logical zero, “0”, if they are programmed.

Table 25-3.

Extended Fuse Byte

Fuse Low Byte

Bit NoDescription

Default Value : 0xF4

–

7

–

1

–

6

–

1

–

5

–

1

–

4

–

1

HWBE

3

Hardware Boot Enable

0 (programmed)

BODLEVEL2(1)

2

Brown-out Detector trigger level1 (unprogrammed)

BODLEVEL1(1)

1

Brown-out Detector trigger level

0 (programmed)

BODLEVEL0(1)0Brown-out Detector trigger level

0 (programmed)

Note:

244

1. See Table 9-2 on page 49 for BODLEVEL Fuse decoding.

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AT90USB82/162
Table 25-4.

Fuse High Byte

Fuse High Byte

Bit NoDescription

Default Value : 0xD9

DWEN(4)

7

Enable debugWIRE (and disable
Reset capability

1 (unprogrammed, debugWIRE
disabled)

RSTDSBL

6

Disable Reset (pin can be used as
general purpose I/O)

1 (unprogrammed, Resetenabled)SPIEN(1)5Enable Serial Program and Data
Downloading

0 (programmed, SPI prog.
enabled)WDTON(3)4Watchdog Timer always ON

1 (unprogrammed)(3)EESAVE

3

EEPROM memory is preserved
through the Chip Erase

1 (unprogrammed, EEPROM
not preserved)

BOOTSZ1

2

Select Boot Size (see Table 25-6 fordetails)0 (programmed)(2)BOOTSZ0

1

Select Boot Size (see Table 25-6 fordetails)0 (programmed)(2)BOOTRST

0

Select Bootloader Address as Reset
Vector1 (unprogrammed, Resetvector @0x0000)

Note:

1. The SPIEN Fuse is not accessible in serial programming mode.
2. The default value of BOOTSZ1..0 results in maximum Boot Size. See Table 23-8 on page 239
for details.
3. See “Watchdog Timer Control Register - WDTCSR” on page 56 for details.
4. Never ship a product with the DWEN Fuse programmed regardless of the setting of Lock bits
and RSTDSBL Fuse. A programmed DWEN Fuse enables some parts of the clock system tobe running in all sleep modes. This may increase the power consumption.

Table 25-5.

Fuse Low Byte

Fuse Low Byte

Description

Default Value : 0x5E

7Divide clock by 80 (programmed)

6

Clock output

1 (unprogrammed)

SUT1

5

Select start-up time

0 (programmed)(1)

SUT0

4

Select start-up time

1 (unprogrammed)(1)

CKSEL3

3

Select Clock source

1 (unprogrammed)(2)CKSEL2

2

Select Clock source

1 (unprogrammed)(2)CKSEL1

1

Select Clock source

1 (unprogrammed)(2)CKSEL00

Select Clock source

0 (programmed)(2)

(4)

(3)

CKDIV8
CKOUT

Note:

Bit No1. The default value of SUT1..0 results in maximum start-up time for the default clock source.
See Table 9-1 on page 47 for details.
2. The default setting of CKSEL3..0 results in external Oscillator. See Table 6-1 on page 29 fordetails.
3. The CKOUT Fuse allow the system clock to be output on PORTC7. See “Clock Output Buffer”
on page 34 for details.
4. See “System Clock Prescaler” on page 34 for details.

The status of the Fuse bits is not affected by Chip Erase. Note that the Fuse bits are locked if
Lock bit1 (LB1) is programmed. Program the Fuse bits before programming the Lock bits.

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25.2.1

25.3

Latching of Fuses
The fuse values are latched when the device enters programming mode and changes of thefuse values will have no effect until the part leaves Programming mode. This does not apply to
the EESAVE Fuse which will take effect once it is programmed. The fuses are also latched on
Power-up in Normal mode.

Signature Bytes
All Atmel microcontrollers have a three-byte signature code which identifies the device. This
code can be read in both serial and parallel mode, also when the device is locked. The threebytes reside in a separate address space.
AT90USB82/162 Signature Bytes:
1. 0x000: 0x1E (indicates manufactured by Atmel).
2. 0x001: 0x94 (indicates 16KB Flash memory).
3. 0x002: 0x82 (indicates AT90USB82/162 device).

25.4

Calibration Byte
The AT90USB82/162 has a byte calibration value for the internal RC Oscillator. This byte
resides in the high byte of address 0x000 in the signature address space. During reset, this byte
is automatically written into the OSCCAL Register to ensure correct frequency of the calibrated
RC Oscillator.

25.5

Parallel Programming Parameters, Pin Mapping, and Commands
This section describes how to parallel program and verify Flash Program memory, EEPROM
Data memory, Memory Lock bits, and Fuse bits in the AT90USB82/162. Pulses are assumed to
be at least 250 ns unless otherwise noted.

25.5.1Signal Names
In this section, some pins of the AT90USB82/162 are referenced by signal names describing
their functionality during parallel programming, see Figure 25-1 and Table 25-6. Pins notdescribed in the following table are referenced by pin names.
The XA1/XA0 pins determine the action executed when the XTAL1 pin is given a positive pulse.
The bit coding is shown in Table 25-9.
When pulsing WR or OE, the command loaded determines the action executed. The different
commands are shown in Table 25-10.

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AT90USB82/162
Figure 25-1. Parallel Programming(1)+5V
RDY/BSY

PD1

OE

PD2

WR

PD3

BS1

PD4

XA0

PD5

XA1

PD6

PAGEL

PD7

+12 V

RESET

BS2

VCC
+5V
AVCC
DATA

PB7:0

PC6
XTAL1
GND

Note:

1. Unused Pins should be left floating.

Table 25-6.

Pin Name Mapping

Signal Name in
Programming Mode

Pin Name

I/O

Function

RDY/BSY

PD1

O

0: Device is busy programming, 1: Device is ready for
new command.

OE

PD2

I

Output Enable (Active low).

WR

PD3

I

Write Pulse (Active low).

BS1

PD4

I

Byte Select 1.

XA0

PD5

I

XTAL Action Bit 0

XA1

PD6

I

XTAL Action Bit 1

PAGEL

PD7

I

Program Memory and EEPROM data Page Load.

BS2

PC6

I

Byte Select 2.

DATA

PB7-0

I/O

Bi-directional Data bus (Output when OE is low).

Table 25-7.

BS2 and BS1 Encoding
Flash Data
Loading /Reading

Fuse
Programming

Reading Fuseand Lock Bits

BS2

BS1

Flash / EEPROM
Address00

Low Byte

Low Byte

Low Byte

Fuse Low Byte

01High Byte

High Byte

High Byte

Lockbits

10

Extended High
Byte

Reserved

Extended Byte

Extended Fuse
Byte

1

1

Reserved

Reserved

Reserved

Fuse High Byte

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Table 25-8.

Pin Values Used to Enter Programming Mode
Pin

Symbol

Value

PAGEL

Prog_enable[3]0

XA1

Prog_enable[2]0

XA0

Prog_enable[1]0BS1

Prog_enable[0]0Table 25-9.

XA1 and XA0 Encoding

XA1

XA0

Action when XTAL1 is Pulsed

00

Load Flash or EEPROM Address (High or low address byte determinedby BS2 and BS1).

0

1

Load Data (High or Low data byte for Flash determined by BS1).

1

0

Load Command

1

1

No Action, Idle

Table 25-10. Command Byte Bit Encoding
Command Byte

Command Executed1000 0000

Chip Erase

0100 0000

Write Fuse bits

0010 0000

Write Lock bits

0001 0000

Write Flash0001 0001

Write EEPROM

0000 1000

Read Signature Bytes and Calibration byte

0000 0100

Read Fuse and Lock bits

0000 0010

Read Flash0000 0011

Read EEPROM

Table 25-11. No. of Words in a Page and No. of Pages in the FlashFlash Size
4/8K words (8/16Kbytes)

Page Size

PCWORDNo. ofPages

PCPAGEPCMSB

64 words

PC[5:0]128

PC[12:6]

12

Table 25-12. No. of Bytes in a Page and No. of Pages in the EEPROM

248

EEPROM Size

Page Size

PCWORDNo. ofPages

PCPAGEEEAMSB

512 bytes

4 bytes

EEA[1:0]128

EEA[8:2]

8

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AT90USB82/162
25.6
25.6.1

Parallel Programming
Enter Programming Mode
The following algorithm puts the device in parallel programming mode:
1. Apply 4.5 - 5.5V between VCC and GND.
2. Set RESET to “0” and toggle XTAL1 at least six times.
3. Set the Prog_enable pins listed in Table 25-8 on page 248 to “0000” and wait at least
100 ns.
4. Apply 11.5 - 12.5V to RESET. Any activity on Prog_enable pins within 100 ns after+12V has been applied to RESET, will cause the device to fail entering programmingmode.
5. Wait at least 50 µs before sending a new command.

25.6.2

Considerations for Efficient Programming
The loaded command and address are retained in the device during programming. For efficient
programming, the following should be considered.
• The command needs only be loaded once when writing or reading multiple memory
locations.
• Skip writing the data value 0xFF, that is the contents of the entire EEPROM (unless the
EESAVE Fuse is programmed) and Flash after a Chip Erase.
• Address high byte needs only be loaded before programming or reading a new 256 word
window in Flash or 256 byte EEPROM. This consideration also applies to Signature bytes
reading.

25.6.3Chip Erase

The Chip Erase will erase the Flash and EEPROM(1) memories plus Lock bits. The Lock bits are
not reset until the program memory has been completely erased. The Fuse bits are notchanged. A Chip Erase must be performed before the Flash and/or EEPROM are
reprogrammed.
Note:

1. The EEPRPOM memory is preserved during Chip Erase if the EESAVE Fuse is programmed.

Load Command “Chip Erase”
1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “1000 0000”. This is the command for Chip Erase.
4. Give XTAL1 a positive pulse. This loads the command.
5. Give WR a negative pulse. This starts the Chip Erase. RDY/BSY goes low.
6. Wait until RDY/BSY goes high before loading a new command.

25.6.4Programming the FlashThe Flash is organized in pages, see Table 25-11 on page 248. When programming the Flash,the program data is latched into a page buffer. This allows one page of program data to be programmed simultaneously. The following procedure describes how to program the entire Flashmemory:A. Load Command “Write Flash”

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1. Set XA1, XA0 to “10”. This enables command loading.
2. Set BS1 to “0”.
3. Set DATA to “0001 0000”. This is the command for Write Flash.
4. Give XTAL1 a positive pulse. This loads the command.
B. Load Address Low byte (Address bits 7..0)
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS2, BS1 to “00”. This selects the address low byte.
3. Set DATA = Address low byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address low byte.
C. Load Data Low Byte
1. Set XA1, XA0 to “01”. This enables data loading.
2. Set DATA = Data low byte (0x00 - 0xFF).
3. Give XTAL1 a positive pulse. This loads the data byte.
D. Load Data High Byte
1. Set BS1 to “1”. This selects high data byte.
2. Set XA1, XA0 to “01”. This enables data loading.
3. Set DATA = Data high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the data byte.
E. Latch Data
1. Set BS1 to “1”. This selects high data byte.
2. Give PAGEL a positive pulse. This latches the data bytes. (See Figure 25-3 for signal
waveforms)
F. Repeat B through E until the entire buffer is filled or until all data within the page is loaded.
While the lower bits in the address are mapped to words within the page, the higher bits address
the pages within the FLASH. This is illustrated in Figure 25-2 on page 251. Note that if less thaneight bits are required to address words in the page (pagesize < 256), the most significant bit(s)in the address low byte are used to address the page when performing a Page Write.
G. Load Address High byte (Address bits15..8)
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS2, BS1 to “01”. This selects the address high byte.
3. Set DATA = Address high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
H. Load Address Extended High byte (Address bits 23..16)
1. Set XA1, XA0 to “00”. This enables address loading.
2. Set BS2, BS1 to “10”. This selects the address extended high byte.
3. Set DATA = Address extended high byte (0x00 - 0xFF).
4. Give XTAL1 a positive pulse. This loads the address high byte.
I. Program Page
1. Set BS2, BS1 to “00”
2. Give WR a negative pulse. This starts programming of the entire page of data.
RDY/BSY goes low.

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AT90USB82/162
3. Wait until RDY/BSY goes high (See Figure 25-3 for signal waveforms).
J. Repeat B through I until the entire Flash is programmed or until all data has been
programmed.
K. End Page Programming
1. 1. Set XA1, XA0 to “10”. This enables command loading.
2. Set DATA to “0000 0000”. This is the command for No Operation.
3. Give XTAL1 a positive pulse. This loads the command, and the internal write signals
are reset.

Figure 25-2. Addressing the Flash Which is Organized in Pages(1)PCMSB
PROGRAM
COUNTERPAGEMSB
PCPAGEPCWORD

PAGE ADDRESSWITHIN THE FLASH

WORD ADDRESSWITHIN A PAGE

PROGRAM MEMORY

PAGE

PAGE

PCWORD[PAGEMSB:0]:00

INSTRUCTION WORD

01
02

PAGEEND

Note:

1. PCPAGE and PCWORD are listed in Table 25-11 on page 248.

Figure 25-3. Programming the Flash Waveforms(1)
F

DATA

A

B

C

D

E

0x10

ADDR. LOWDATA LOWDATA HIGH

XX

B
ADDR. LOWCDEDATA LOWDATA HIGH

XX

G

H

ADDR. HIGH ADDR. EXT.H

I
XX

XA1
XA0
BS1

BS2
XTAL1
WR
RDY/BSYRESET +12V
OE
PAGEL

Note:

1. “XX” is don’t care. The letters refer to the programming description above.

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25.6.5

Programming the EEPROM
The EEPROM is organized in pages, see Table 25-12 on page 248. When programming the
EEPROM, the program data is latched into a page buffer. This allows one page of data to be
programmed simultaneously. The programming algorithm for the EEPROM data memory is asfollows (refer to “Programming the Flash” on page 249 for details on Command, Address andData loading):
1. A: Load Command “0001 0001”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. C: Load Data (0x00 - 0xFF).
5. E: Latch data (give PAGEL a positive pulse).
K: Repeat 3 through 5 until the entire buffer is filled.
L: Program EEPROM page
1. Set BS2, BS1 to “00”.
2. Give WR a negative pulse. This starts programming of the EEPROM page. RDY/BSY
goes low.
3. Wait until to RDY/BSY goes high before programming the next page (See Figure 25-4
for signal waveforms).

Figure 25-4. Programming the EEPROM Waveforms
K

DATA

A

G

B

C

E

0x11

ADDR. HIGH

ADDR. LOW

DATA

XX

B
ADDR. LOW

C

E

DATA

XX

L

XA1
XA0
BS1
XTAL1
WR
RDY/BSYRESET +12V
OE
PAGEL
BS2

25.6.6

Reading the FlashThe algorithm for reading the Flash memory is as follows (refer to “Programming the Flash” onpage 249 for details on Command and Address loading):
1. A: Load Command “0000 0010”.
2. H: Load Address Extended Byte (0x00- 0xFF).
3. G: Load Address High Byte (0x00 - 0xFF).
4. B: Load Address Low Byte (0x00 - 0xFF).
5. Set OE to “0”, and BS1 to “0”. The Flash word low byte can now be read at DATA.
6. Set BS to “1”. The Flash word high byte can now be read at DATA.
7. Set OE to “1”.

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AT90USB82/162
25.6.7

Reading the EEPROM
The algorithm for reading the EEPROM memory is as follows (refer to “Programming the Flash”
on page 249 for details on Command and Address loading):
1. A: Load Command “0000 0011”.
2. G: Load Address High Byte (0x00 - 0xFF).
3. B: Load Address Low Byte (0x00 - 0xFF).
4. Set OE to “0”, and BS1 to “0”. The EEPROM Data byte can now be read at DATA.
5. Set OE to “1”.

25.6.8Programming the Fuse Low Bits
The algorithm for programming the Fuse Low bits is as follows (refer to “Programming the Flash”
on page 249 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Give WR a negative pulse and wait for RDY/BSY to go high.

25.6.9Programming the Fuse High Bits
The algorithm for programming the Fuse High bits is as follows (refer to “Programming theFlash” on page 249 for details on Command and Data loading):
1. A: Load Command “0100 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. Set BS2, BS1 to “01”. This selects high data byte.
4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. Set BS2, BS1 to “00”. This selects low data byte.

25.6.10Programming the Extended Fuse Bits
The algorithm for programming the Extended Fuse bits is as follows (refer to “Programming theFlash” on page 249 for details on Command and Data loading):
1. 1. A: Load Command “0100 0000”.
2. 2. C: Load Data Low Byte. Bit n = “0” programs and bit n = “1” erases the Fuse bit.
3. 3. Set BS2, BS1 to “10”. This selects extended data byte.
4. 4. Give WR a negative pulse and wait for RDY/BSY to go high.
5. 5. Set BS2, BS1 to “00”. This selects low data byte.

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Figure 25-5. Programming the FUSES Waveforms
Write Fuse Low byte

DATA

A

C

0x40

DATA

XX

Write Fuse high byte
A

C

0x40

DATA

XX

Write Extended Fuse byte
A

C

0x40

DATA

XX

XA1

XA0

BS1

BS2

XTAL1

WR

RDY/BSYRESET +12V

OE

PAGEL

25.6.11

Programming the Lock Bits
The algorithm for programming the Lock bits is as follows (refer to “Programming the Flash” onpage 249 for details on Command and Data loading):
1. A: Load Command “0010 0000”.
2. C: Load Data Low Byte. Bit n = “0” programs the Lock bit. If LB mode 3 is programmed(LB1 and LB2 is programmed), it is not possible to program the Boot Lock bits by any
External Programming mode.
3. Give WR a negative pulse and wait for RDY/BSY to go high.
The Lock bits can only be cleared by executing Chip Erase.

25.6.12

Reading the Fuse and Lock Bits
The algorithm for reading the Fuse and Lock bits is as follows (refer to “Programming the Flash”
on page 249 for details on Command loading):
1. A: Load Command “0000 0100”.
2. Set OE to “0”, and BS2, BS1 to “00”. The status of the Fuse Low bits can now be readat DATA (“0” means programmed).
3. Set OE to “0”, and BS2, BS1 to “11”. The status of the Fuse High bits can now be readat DATA (“0” means programmed).
4. Set OE to “0”, and BS2, BS1 to “10”. The status of the Extended Fuse bits can now beread at DATA (“0” means programmed).
5. Set OE to “0”, and BS2, BS1 to “01”. The status of the Lock bits can now be read at
DATA (“0” means programmed).
6. Set OE to “1”.

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AT90USB82/162

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AT90USB82/162
Figure 25-6. Mapping Between BS1, BS2 and the Fuse and Lock Bits During Read0

Fuse Low Byte0
Extended Fuse Byte

1

DATA

BS2
0

Lock Bits

1

Fuse High Byte

BS1

1
BS2

25.6.13

Reading the Signature Bytes
The algorithm for reading the Signature bytes is as follows (refer to “Programming the Flash” onpage 249 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte (0x00 - 0x02).
3. Set OE to “0”, and BS to “0”. The selected Signature byte can now be read at DATA.
4. Set OE to “1”.

25.6.14

Reading the Calibration Byte
The algorithm for reading the Calibration byte is as follows (refer to “Programming the Flash” onpage 249 for details on Command and Address loading):
1. A: Load Command “0000 1000”.
2. B: Load Address Low Byte, 0x00.
3. Set OE to “0”, and BS1 to “1”. The Calibration byte can now be read at DATA.
4. Set OE to “1”.

25.6.15

Parallel Programming Characteristics
Figure 25-7. Parallel Programming Timing, Including some General Timing Requirements
tXLWL
XTAL1
Data & Contol(DATA, XA0/1, BS1, BS2)
PAGEL
WR

tXHXL
tDVXH

tXLDX
tPLBX t BVWL

tBVPH
tPHPL

tWLBX
tWLWH

tPLWL

WLRL

RDY/BSYtWLRH

255
7707E–AVR–11/08

Figure 25-8. Parallel Programming Timing, Loading Sequence with Timing Requirements(1)LOAD ADDRESS(LOW BYTE)LOAD DATA LOAD DATA(HIGH BYTE)LOAD DATA(LOW BYTE)

tXLPH

t XLXHLOAD ADDRESS(LOW BYTE)

tPLXH

XTAL1

BS1

PAGEL

DATA

ADDR0 (Low Byte)

DATA (Low Byte)

DATA (High Byte)

ADDR1 (Low Byte)

XA0

XA1

Note:

1. The timing requirements shown in Figure 25-7 (i.e., tDVXH, tXHXL, and tXLDX) also apply to loading operation.

Figure 25-9. Parallel Programming Timing, Reading Sequence (within the Same Page) with
Timing Requirements(1)LOAD ADDRESS(LOW BYTE)

READ DATA(LOW BYTE)

READ DATA(HIGH BYTE)LOAD ADDRESS(LOW BYTE)

tXLOL

XTAL1
tBVDV

BS1
tOLDV

OE

DATA

tOHDZ

ADDR0 (Low Byte)

DATA (Low Byte)

ADDR1 (Low Byte)

DATA (High Byte)

XA0

XA1

Note:

1. The timing requirements shown in Figure 25-7 (i.e., tDVXH, tXHXL, and tXLDX) also apply to reading operation.

Table 25-13. Parallel Programming Characteristics, VCC = 5V ± 10%256

SymbolParameter

Min

VPP

Programming Enable Voltage

11.5

IPP

Programming Enable Current

tDVXH

Data and Control Valid before XTAL1 High

67

ns

tXLXH

XTAL1 Low to XTAL1 High

200

ns

tXHXL

XTAL1 Pulse Width High

150

ns

tXLDX

Data and Control Hold after XTAL1 Low

67

ns

AT90USB82/162

Typ

Max

Units

12.5

V

250

μA

7707E–AVR–11/08

AT90USB82/162
Table 25-13. Parallel Programming Characteristics, VCC = 5V ± 10% (Continued)
SymbolParameter

Min

tXLWL

XTAL1 Low to WR Low

0

ns

tXLPH

XTAL1 Low to PAGEL high

0

ns

tPLXH

PAGEL low to XTAL1 high

150

ns

tBVPH

BS1 Valid before PAGEL High

67

ns

tPHPL

PAGEL Pulse Width High

150

ns

tPLBX

BS1 Hold after PAGEL Low

67

ns

tWLBX

BS2/1 Hold after WR Low

67

ns

tPLWL

PAGEL Low to WR Low

67

ns

tBVWL

BS2/1 Valid to WR Low

67

ns

tWLWH

WR Pulse Width Low

150

ns

tWLRL

WR Low to RDY/BSY Low

0

1

μs

tWLRH

WR Low to RDY/BSY High(1)

3.7

4.5

ms

9

ms

tWLRH_CEWR Low to RDY/BSY High for Chip Erase

7.5

tXLOL

XTAL1 Low to OE Low

0

tBVDV

BS1 Valid to DATA valid

0

tOLDV
tOHDZ
Notes:

25.7

(2)

Typ

Max

Units

ns
250

ns

OE Low to DATA Valid

250

ns

OE High to DATA Tri-stated

250

ns

1.

tWLRH is valid for the Write Flash, Write EEPROM, Write Fuse bits and Write Lock bits
commands.

2.

tWLRH_CE is valid for the Chip Erase command.

Serial Downloading
Both the Flash and EEPROM memory arrays can be programmed using a serial programmingbus while RESET is pulled to GND. The serial programming interface consists of pins SCK, PDI(input) and PDO (output). After RESET is set low, the Programming Enable instruction needs tobe executed first before program/erase operations can be executed. NOTE, in Table 25-14 on
page 257, the pin mapping for serial programming is listed. Not all packages use the SPI pins
dedicated for the internal Serial Peripheral Interface - SPI.

25.8

Serial Programming Pin Mapping
Table 25-14. Pin Mapping Serial Programming
SymbolPins

I/O

Description

PDI

PB2

I

Serial Data in

PDO

PB3

O

Serial Data out

SCK

PB1

I

Serial Clock

Figure 25-10. Serial Programming and Verify(1)2577707E–AVR–11/08

+1.8 - 5.5V
VCC
+1.8 - 5.5V(2)
PDI

AVCC

PDO
SCK
XTAL1

RESET

GND

Notes:

1. If the device is clocked by the internal Oscillator, it is no need to connect a clock source to the
XTAL1 pin.
2. VCC - 0.3V < AVCC < VCC + 0.3V, however, AVCC should always be within 1.8 - 5.5V

When programming the EEPROM, an auto-erase cycle is built into the self-timed programming
operation (in the Serial mode ONLY) and there is no need to first execute the Chip Erase
instruction. The Chip Erase operation turns the content of every memory location in both theProgram and EEPROM arrays into 0xFF.
Depending on CKSEL Fuses, a valid clock must be present. The minimum low and high periods
for the serial clock (SCK) input are defined as follows:
Low: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz
High: > 2 CPU clock cycles for fck < 12 MHz, 3 CPU clock cycles for fck >= 12 MHz

25.8.1

Serial Programming Algorithm
When writing serial data to the AT90USB82/162, data is clocked on the rising edge of SCK.
When reading data from the AT90USB82/162, data is clocked on the falling edge of SCK. See
Figure 25-11 for timing details.
To program and verify the AT90USB82/162 in the serial programming mode, the following
sequence is recommended (See four byte instruction formats in Table 25-16):
1. Power-up sequence:
Apply power between VCC and GND while RESET and SCK are set to “0”. In some systems, the programmer can not guarantee that SCK is held low during power-up. In thiscase, RESET must be given a positive pulse of at least two CPU clock cycles duration
after SCK has been set to “0”.
2. Wait for at least 20 ms and enable serial programming by sending the Programming
Enable serial instruction to pin PDI.
3. The serial programming instructions will not work if the communication is out of synchronization. When in sync. the second byte (0x53), will echo back when issuing thethird byte of the Programming Enable instruction. Whether the echo is correct or not, allfour bytes of the instruction must be transmitted. If the 0x53 did not echo back, give
RESET a positive pulse and issue a new Programming Enable command.
4. The Flash is programmed one page at a time. The memory page is loaded one byte ata time by supplying the 7 LSB of the address and data together with the Load Program

258

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AT90USB82/162
Memory Page instruction. To ensure correct loading of the page, the data low byte must
be loaded before data high byte is applied for a given address. The Program Memory
Page is stored by loading the Write Program Memory Page instruction with the addresslines 15..8. Before issuing this command, make sure the instruction Load Extended
Address Byte has been used to define the MSB of the address. The extended address
byte is stored until the command is re-issued, i.e., the command needs only to beissued for the first page, since the memory size is not larger than 64KWord. If polling(RDY/BSY) is not used, the user must wait at least tWD_FLASH before issuing the next
page. (See Table 25-15.) Accessing the serial programming interface before the Flashwrite operation completes can result in incorrect programming.
5. The EEPROM array is programmed one byte at a time by supplying the address anddata together with the appropriate Write instruction. An EEPROM memory location is
first automatically erased before new data is written. If polling is not used, the user must
wait at least tWD_EEPROM before issuing the next byte. (See Table 25-15.) In a chiperased device, no 0xFFs in the data file(s) need to be programmed.
6. Any memory location can be verified by using the Read instruction which returns thecontent at the selected address at serial output PDO. When reading the Flash memory,
use the instruction Load Extended Address Byte to define the upper address byte,
which is not included in the Read Program Memory instruction. The extended address
byte is stored until the command is re-issued, i.e., the command needs only to beissued for the first page, since the memory size is not larger than 64KWord.
7. At the end of the programming session, RESET can be set high to commence normal
operation.
8. Power-off sequence (if needed):
Set RESET to “1”.
Turn VCC power off.

Table 25-15. Minimum Wait Delay Before Writing the Next Flash or EEPROM Location
SymbolMinimum Wait DelaytWD_FLASH

4.5 mstWD_EEPROM

9.0 mstWD_ERASE

9.0 msFigure 25-11. Serial Programming Waveforms
SERIAL DATA INPUT(MOSI)MSBLSBSERIAL DATA OUTPUT(MISO)MSBLSBSERIAL CLOCK INPUT(SCK)SAMPLE

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Table 25-16. Serial Programming Instruction Set
Instruction Format
Instruction

Byte 1

Byte 2Byte 3

Byte4

Programming Enable

1010 1100

0101 0011

xxxx xxxx

xxxx xxxx

Enable Serial Programming after
RESET goes low.

Chip Erase

1010 1100

100x xxxx

xxxx xxxx

xxxx xxxx

Chip Erase EEPROM and Flash.

0100 1101

0000 0000

cccc cccc

xxxx xxxx

Defines Extended Address Byte for
Read Program Memory and Write
Program Memory Page.

0010 H000

aaaa aaaa

bbbb bbbb

oooo oooo

Read H (high or low) data o from
Program memory at word address
c:a:b.

0100 H000

xxxx xxxx

xxbb bbbb

iiii iiii

Write H (high or low) data i to Program
Memory page at word address b. Data
low byte must be loaded before Datahigh byte is applied within the same
address.

Write Program Memory Page

0100 1100

aaaa aaaa

bbxx xxxx

xxxx xxxx

Write Program Memory Page ataddress c:a:b.

Read EEPROM Memory

1010 0000

0000 aaaa

bbbb bbbb

oooo oooo

Read data o from EEPROM memory ataddress a:b.

Write EEPROM Memory

1100 0000

0000 aaaa

bbbb bbbb

iiii iiii

Write data i to EEPROM memory ataddress a:b.

Load EEPROM Memory
Page (page access)1100 0001

0000 0000

0000 00bb

iiii iiii

Load data i to EEPROM memory page
buffer. After data is loaded, program
EEPROM page.

Write EEPROM Memory
Page (page access)1100 0010

0000 aaaa

bbbb bb00

xxxx xxxx

Write EEPROM page at address a:b.

0101 1000

0000 0000

xxxx xxxx

xxoo oooo

Read Lock bits. “0” = programmed, “1”= unprogrammed. See Table 25-1 onpage 243 for details.

1010 1100

111x xxxx

xxxx xxxx

11ii iiii

Write Lock bits. Set bits = “0” toprogram Lock bits. See Table 25-1 onpage 243 for details.

Read Signature Byte

0011 0000

000x xxxx

xxxx xxbb

oooo oooo

Read Signature Byte o at address b.

Write Fuse bits

1010 1100

1010 0000

xxxx xxxx

iiii iiii

Set bits = “0” to program, “1” tounprogram.

Write Fuse High bits

1010 1100

1010 1000xxxx xxxx

iiii iiii

Set bits = “0” to program, “1” tounprogram.

1010 1100

1010 0100

xxxx xxxx

iiii iiii

Set bits = “0” to program, “1” tounprogram. See Table 25-3 on page244 for details.

Read Fuse bits

0101 0000

0000 0000

xxxx xxxx

oooo oooo

Read Fuse bits. “0” = programmed, “1”= unprogrammed.

Read Fuse High bits

0101 1000

0000 1000xxxx xxxx

oooo oooo

Read Fuse High bits. “0” = programmed, “1” = unprogrammed.

Load Extended Address Byte

Read Program Memory

Load Program Memory Page

Read Lock bits

Write Lock bits

Write Extended Fuse Bits

260

AT90USB82/162

Operation

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AT90USB82/162
Table 25-16. Serial Programming Instruction Set (Continued)
Instruction Format
Instruction

Byte 1

Byte 2Byte 3Byte40101 0000

0000 1000xxxx xxxx

oooo oooo

Read Extended Fuse bits. “0” = programmed, “1” = unprogrammed. See
Table 25-3 on page 244 for details.

0011 1000

000x xxxx

0000 0000

oooo oooo

Read Calibration Byte

1111 0000

0000 0000

xxxx xxxx

xxxx xxxo

If o = “1”, a programming operation isstill busy. Wait until this bit returns to“0” before applying another command.

Read Extended Fuse Bits
Read Calibration Byte
Poll RDY/BSY
Note:

25.8.2

Operationa = address high bits, b = address low bits, c = address extended bits, H = 0 - Low byte, 1 - High Byte, o = data out, i = data in,
x = don’t care

Serial Programming Characteristics
For characteristics of the Serial Programming module see “SPI Timing Characteristics” on page
265.

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26. Electrical Characteristics
26.1

Absolute Maximum Ratings*

Operating Temperature....................................-55⋅C to +125⋅C*NOTICE:

Storage Temperature ..................................... -65°C to +150°C
Voltage on any Pin except RESET & UVcc
with respect to Ground(7) .............................-0.5V to VCC+0.5V
Voltage on RESET with respect to Ground......-0.5V to +13.0V
Voltage on UVcc with respect to Ground ...........-0.5V to +6.0V

Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent damage to the device. This is a stress rating only andfunctional operation of the device at these orother conditions beyond those indicated in theoperational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affectdevice reliability.

Maximum Operating Voltage ............................................ 6.0V
DC Current per I/O Pin ............................................... 40.0 mA
DC Current VCC and GND Pins................................ 200.0 mA

26.2

DC Characteristics

TA = -40⋅C to 85⋅C, VCC = 2.7V to 5.5V (unless otherwise noted)
SymbolParameter

Condition

Min.(5)Max.(5)

Units

VIL

Input Low Voltage,
Standard IOs(8)VCC = 2.7V - 5.5V

-0.5

0.2VCC(1)V

VIL1

Input Low Voltage,
XTAL1 pin

VCC = 2.7V - 5.5V

-0.5

0.1VCC(1)V

VIL2

Input Low Voltage,RESET pin

VCC = 2.7V - 5.5V

-0.5

0.1VCC(1)V

VIL3

Input Low Voltage,
MOSI/MISO pins

VCC = 2.7V - 5.5V

-0.5

0.8

V

VIL4

Input Low Voltage, PS2
pins

VCC = 4.5V - 5.5V

-0.5

0.7

V

VIH

Input High Voltage,
Standard IOs(8)VCC = 2.7V - 5.5V

0.6VCC(2)VCC + 0.5

V

VIH1

Input High Voltage,
XTAL1 pin

VCC = 2.7V - 5.5V

0.7VCC(2)VCC + 0.5

V

VIH2

Input High Voltage,RESET pin

VCC = 2.7V - 5.5V

0.9VCC(2)VCC + 0.5

V

VIH3

Input High Voltage,
MOSI/MISO pins

VCC = 2.7V - 5.5V

2

VCC + 0.5

V

VIH4

Input High Voltage, PS2
pins

VCC = 4.5V - 5.5V

2.4

VCC + 0.5

VVOL

Output Low Voltage(3),Standard IOs(8),MOSI/MISO pins

IOL = 10mA, VCC = 5V
IOL = 5mA, VCC = 3V

0.7
0.5

V

262

AT90USB82/162

Typ.

7707E–AVR–11/08

AT90USB82/162
TA = -40⋅C to 85⋅C, VCC = 2.7V to 5.5V (unless otherwise noted) (Continued)
Min.(5)

Units

0.7

V

Parameter

Condition

VOL1

Output Low Voltage, PS2
pins

IOL = 5mA,
VCC = 4.5 - 5.5V

VOH

Output High Voltage(4),Standard IOs(8),MOSI/MISO pins

IOH = -20mA, VCC = 5V
IOH = -10mA, VCC = 3V

IIL

Input Leakage
Current I/O Pin

VCC = 5.5V, pin low(absolute value)

1

µA

IIH

Input Leakage
Current I/O Pin

VCC = 5.5V, pin high(absolute value)

1

µA

RRST

Reset Pull-up Resistor

30

60

kΩ

RPU

I/O Pin Pull-up Resistor

20

50

kΩ

RPUDP

USD D+ Internal Pull-Up

900

1500

Ω

RPUPS2PS2 Pull-up Resistor

4.7

6.5

kΩ

Active 8MHz, VCC = 3V

7

8.5

mA

Active 16MHz, VCC = 5V

13.5

25

mA

Idle 8MHz, VCC = 3V

3.5

Idle 16MHz, VCC = 5V

4

4.5

mA

WDT disabled, Regulator
Disabled,VCC = 3V

5

10

µA

WDT enabled, Regulator
Disabled,VCC = 3V

10

15

µA

WDT, BOD, Regulator
Enabled, Vcc = 5V

41

65

µA

WDT, BOD Enabled,
Regulator Disabled, Vcc
= 3V

70

100

µA

WDT, BOD, Regulator
Enabled, Vcc = 5V

120

150

µA

<10

40

mV

50

nA

Power Supply Current(6)ICC

Power-down modeStandby mode

VCC = 5V

VACIO

Analog Comparator
Input Offset Voltage

VCC = 5V
Vin = VCC/2

IACLK

Analog Comparator
Input Leakage Current

VCC = 5V
Vin = VCC/2

tACID

Analog Comparator
Propagation Delay

VCC = 2.7V
VCC = 4.0V

Rusb

USB Series resistor(external)

Vreg
Note:

4.2
2.3

3.2

V

-50

Vcc 4.0V, I≤100mA,
3.0
CUCAP=1µF±20%
1. "Max" means the highest value where the pin is guaranteed to be read as low
Regulator Output Voltage

Typ.

Max.(5)

Symbol

mA

750
500

ns

22±5%

Ω

3.3

3.6

V

2. "Min" means the lowest value where the pin is guaranteed to be read as high
3. Although each I/O port can sink more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steady state
conditions (non-transient), the following must be observed:
1.)The sum of all IOL, for ports B0-B7, C0-C7, D0-D7 should not exceed 150 mA.

263
7707E–AVR–11/08

4.

5.
6.
7.
8.

26.3

If IOL exceeds the test condition, VOL may exceed the related specification. Pins are not guaranteed to sink current greaterthan the listed test condition.
Although each I/O port can source more than the test conditions (20mA at VCC = 5V, 10mA at VCC = 3V) under steadystate conditions (non-transient), the following must be observed:
1.)The sum of all IOL, for ports B0-B7, C0-C7, D0-D7 should not exceed 150 mA.
If IOH exceeds the test condition, VOH may exceed the related specification. Pins are not guaranteed to source current
greater than the listed test condition.
All DC Characteristics contained in this datasheet are based on simulation and characterization of other AVR microcontrollers manufactured in the same process technology. These values are preliminary values representing design targets, andwill be updated after characterization of actual silicon
Values with “Power Reduction Register 1 - PRR1” disabled (0x00).
As specified in the USB Electrical chapter, the D+/D- pads can withstand voltages down to -1V applied through a 39Ω resistor (in series with the external 22Ω resistor).
All IOs Except XTAL1, MOSI, MISO, PS2 and Reset pins

External Clock Drive Waveforms
Figure 26-1. External Clock Drive Waveforms

V IH1
V IL1

26.4

External Clock Drive
Table 26-1.

VCC=2.7-5.5V

VCC=4.5-5.5V

SymbolParameter

Min.

Max.

Min.

Max.

Units

1/tCLCL

Oscillator
Frequency

0

8

0

16

MHz

tCLCL

Clock Period

125

62.5

ns

tCHCX

High Time

50

25

ns

tCLCX

Low Time

50

25

ns

tCLCH

Rise Time

1.6

0.5

μs

tCHCL

Fall Time

1.6

0.5

μs

ΔtCLCL

Change in period
from one clock
cycle to the next

2

2

%

Note:

264

External Clock Drive

All DC Characteristics contained in this datasheet are based on simulation and characterization ofother AVR microcontrollers manufactured in the same process technology. These values are preliminary values representing design targets, and will be updated after characterization of actual
silicon.

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
26.5

Maximum speed vs. VCC
Maximum frequency is depending on VCC. As shown in Figure 26-2, the Maximum Frequency vs.
VCC curve is linear between 2.7V < VCC < 4.5V.

Figure 26-2. Maximum Frequency vs. VCC, AT90USB82/162

16 MHz

8 MHz

Safe Operating Area

2.7V

26.6

4.5V

5.5V

SPI Timing Characteristics
See Figure 26-3 and Figure 26-3 for details.

Table 26-2.

SPI Timing Parameters
Description

Mode

Min

Typ

1

SCK period

MasterSee Table 16-4

2

SCK high/low

Master

50% duty cycle

3

Rise/Fall time

Master

TBD

4

Setup

Master

10

5

Hold

Master10

6

Out to SCK

Master

0.5 • tsck

7

SCK to out

Master

10

8

SCK to out highMaster10

9

SS low to out

Slave

15

10

SCK periodSlave

4 • tck

11

SCK high/low(1)Slave

2 • tck

12

Rise/Fall time

Slave

13

Setup

Slave

10

14

Hold

Slave

tck

15

SCK to out

Slave

16

SCK to SS high

Slave

17

SS high to tri-state

Slave

18

SS low to SCK

Slave

Max

ns

TBD

15
20
10
20

265
7707E–AVR–11/08

Note:

1. In SPI Programming mode the minimum SCK high/low period is:- 2 tCLCL for fCK < 12 MHz- 3 tCLCL for fCK > 12 MHz

Figure 26-3. SPI Interface Timing Requirements (Master Mode)
SS
6

1

SCK
(CPOL = 0)2

SCK(CPOL = 1)

4

MISO
(Data Input)

5

3

MSB

...

LSB

7

MOSI
(Data Output)

Table 26-3.

2

8

MSB

...

LSB

SPI Interface Timing Requirements (Slave Mode)
SS
10

9

SCK
(CPOL = 0)SCK(CPOL = 1)
MOSI
(Data Input)
MISO(Data Output)

26.7

16

11

13

11

14

12

MSB

...

LSB

15

17

MSB

...

LSB

X

Hardware Boot EntranceTiming Characteristics
Figure 26-4. Hardware Boot Timing Requirements

RESET

tSHRH

tHHRH

ALE/HWB

266

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162

Table 26-4.

Hardware Boot Timings

SymbolParameter

Min

tSHRH

HWB low Setup before Reset High

0

tHHRH

HWB low Hold after Reset HighMax

StartUpTime(SUT) +Time Out
Delay(TOUT)

267
7707E–AVR–11/08

27. AT90USB82/162 Typical Characteristics – Preliminary Data
The following charts show typical behavior. These figures are not tested during manufacturing.
All current consumption measurements are performed with all I/O pins configured as inputs andwith internal pull-ups enabled. A sine wave generator with rail-to-rail output is used as clock
source.
All Active- and Idle current consumption measurements are done with all bits in the PRR registers set and thus, the corresponding I/O modules are turned off. Also the Analog Comparator isdisabled during these measurements.
The power consumption in Power-down mode is independent of clock selection.
The current consumption is a function of several factors such as: operating voltage, operating
frequency, loading of I/O pins, switching rate of I/O pins, code executed and ambient temperature. The dominating factors are operating voltage and frequency.
The current drawn from capacitive loaded pins may be estimated (for one pin) as CL*VCC*f where
CL = load capacitance, VCC = operating voltage and f = average switching frequency of I/O pin.
The parts are characterized at frequencies higher than test limits. Parts are not guaranteed tofunction properly at frequencies higher than the ordering code indicates.
The difference between current consumption in Power-down mode with Watchdog Timerenabled and Power-down mode with Watchdog Timer disabled represents the differential current drawn by the Watchdog Timer.

268

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.1

Input Voltage Levels
Figure 27-1. Input Low Voltage vs. Vcc, all I/Os excluding DP/DM and MOSI/MISO
2.5

Threshold (V)

2

1.5

1

0.5

0
2

2.5

3

3.5

4

4.5

5

5.5

V CC (V)Figure 27-2. Input High Voltage vs. Vcc, all I/Os excluding DP/DM and MOSI/MISO

2.5

Threshold (V)

2

1.5

1

0.5

0
2.5

3

3.5

4

4.5

5

5.5

V CC (V)269
7707E–AVR–11/08

Figure 27-3. Input Low Voltage vs. Vcc for MOSI/MISO I/Os

2.5

Threshold (V)

2

85°C

1.5

25°C
-40°C

1

0.5

0
2.5

3

3.5

4

4.5

5

5.5

V CC (V)Figure 27-4. Input High Voltage vs. Vcc, MOSI/MISO I/Os

2.5
2.5

ThresholdThreshold(V)
(V)

2
2

85°C
85
25°C
25

1.5
1.5

-40°C
-40

1
1

0.5
0.5

0
0

2.5
2.5

3
3

3.5
3.5

4
4

4.5
4.5

5
5

5.5
5.5

V
(V)
V CC
(V)
CC

270

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.2

Output Voltage Levels
Figure 27-5. Output Low Voltage vs. Output Current, all I/Os excluding DP/DM, Vcc=3V

1
0.9
0.8
0.7

85

V OL (V)

0.6

25

0.5

-40

0.4
0.3
0.2
0.1
0
0

5

10

15

20

25

IOL (mA)

Figure 27-6. Output Low Voltage vs. Output Current, all I/Os excluding DP/DM, Vcc=5V

0.7
0.6
0.5

V OL (V)

0.4

85

0.3

25
-40

0.2
0.1
0
0

5

10

15

20

25

-0.1
IOL (mA)

271
7707E–AVR–11/08

Figure 27-7. Output Low Voltage vs. Output Current, PS2 I/Os, Vcc=5V

1.2
1.2
1

1

0.8
0.8

85°C
85°C

V OL (V)V OL (V)

0.6
0.6

25°C
25°C

0.4

-40°C
-40°C

0.4
0.2
0.2
0
0
0
-0.2

272

5
0

2

10
4

AT90USB82/162

6

15
8

10
IOL (mA)
IOL (mA)

12

20
14

25
16

18

20

7707E–AVR–11/08

AT90USB82/162
Figure 27-8. Output High Voltage vs. Output Current, all I/Os excluding DP/DM, Vcc=3V

3.5
3

V OH (V)

2.5

85

2

25
-40

1.5
1
0.5
0
0

5

10

15

20

25

IOH (mA)

Figure 27-9. Output High Voltage vs. Output Current, all I/Os excluding DP/DM, Vcc=5V

5
4.9
4.8

85

V OH (V)

4.7

25

4.6

-40

4.5
4.4
4.3
4.2
0

5

10

15

20

25

IOH (mA)

273
7707E–AVR–11/08

27.3

I/O Pull-up Current
Figure 27-10. Standard I/O Pull-Up Current vs. Pin Voltage, Vcc=5V
140
140
120
120

IOP (uA)
IOP (uA)

100
100
8080

85
25

6060

-40

40
40
20
20
0
0
-20 0
0

274

1

1

AT90USB82/162

2

2
V OP (V)V OP (V)

3

3

4

4

5

5

7707E–AVR–11/08

AT90USB82/162
27.4

Power-down Supply Current
Figure 27-11. Power-down Supply Current vs. Vcc, with BOD Disabled, WDT Disabled, Regulator Disabled
20
18
16
14

85

ICC (uA)

12

25

10
8
6
4
2
0
2

2.5

3

3.5

4

4.5

5

5.5

6

V CC (V)Figure 27-12. Power-down Supply Current vs. Vcc, with BOD Disabled, WDT Enabled, Regulator Disabled
50
45
40

ICC (uA)

35
30

85

25

25

20
15
10
5
0
2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

V CC (V)275
7707E–AVR–11/08

Figure 27-13. Power-down Supply Current vs. Vcc, with BOD Enabled, Watchdog Disabled

70
60

ICC (uA)

50

85°C

40

25°C

30
20
10
0
3

3.5

4

4.5

5

5.5

V CC (V)Figure 27-14. Power-down Supply Current vs. Vcc, with BOD Enabled, WDT Enabled, Regulator Disabled
WATCHDOG TIMER ENABLED, BODEN
100
90

70

80

60

70

50
ICC (uA)

ICC (uA)

60
50
40

85
25

40
30

30

20

20

10

10

0
3

0
3

3.5

3.5

4

4

4.5

4.5
V CC (V)

5

5

5.5

5.5

6

V CC (V)276

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
Figure 27-15. Power-down Supply Current vs. Vcc, with BOD Enabled, Regulator Enabled

100

75

90

65

80

55

70
45
ICC (uA)

ICC (uA)

60
50
40

85
25

35

-40

25

30

15

20

5

10

-5 2

0
2

2.5

2.5

3

3

3.5

3.5

4

4
V

V CC 4.5
(V)

4.5

5

5

5.5

5.5

6

6

(V)

277
7707E–AVR–11/08

27.5

Idle Supply Current
Figure 27-16. Idle Supply Current vs. Frequency and Vcc, T=25°C, Regulator Disabled (below
4V)

6

5

5.5

ICC (mA)

4

5
4.5

3

4
3.3

2

1

0
0

2

4

6

8

10

12

14

16

Frequency (MHz)278

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.6

Active Supply Current
Figure 27-17. Active Supply Current vs Frequency and Vcc, T=25°C

20
18
16
14
ICC (mA)

12

5.5

10

5

8

4.5
3.6

6

2.7

4
2
0
0

2

4

6

8

10

12

14

16

Frequency (MHz)27.7

Reset Supply Current
Figure 27-18. Reset Supply Current vs Frequency and Vcc

1210

ICC (mA)

8
6

5.5
5

4

4.5
3.3

2

2.7

0
4

6

8

10

12

14

16

Frequency (MHz)279
7707E–AVR–11/08

Figure 27-19. Reset Pull-Up Current vs. Pin Voltage, Vcc=5V

120

100

IRESET (uA)

80

85°C
-40°C

60

40

20

0
0

1

2

3

4

5

6

V RESET (V)

27.8

Bandgap Voltage
Figure 27-20. Bandgap voltage vs. Vcc, vs. Temperature

1.15
1.14

Bandgap Voltage (V)

1.13
1.12

85

1.11

25

1.1

-40

1.09
1.08
1.07
1.06
1.05
2

2.5

3

3.5

4

4.5

5

5.5

Vcc (V)280

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.9

USB Regulator
Figure 27-21. USB Regulator Output Voltage vs. Input Voltage, No Load

3.4
3.4
3.3
3.3

OutputCurrent
Volage(V)
(V)

3.2
3.2

85°C
85°C
-40°C
-40°C

3.1
3.1
3
3
2.9
2.9
2.8
2.8
2.7
2.7 3
3

3.5
3.5

4
4

4.5
4.5
Voltage (V)Voltage (V)

5
5

5.5
5.5

6
6

Figure 27-22. USB Regulator Output Voltage vs. Input Voltage, Load=75 Ohms

3.4
3.4
3.23.2
3 3
Current (V)Voltage (V)

85
85
25
25

2.82.8-40-40

2.62.62.42.42.22.22 2
3 3

3.53.5

4 4

4.5
4.5

55

5.5
5.5

66

Voltage(V)
Voltage(V)

Note:

The 75 Ohms load is equivalent to the maximum average consumption of the USB peripheral inoperation (full bus load)

281
7707E–AVR–11/08

27.10 Power-On Reset
Figure 27-23. Power-On Reset Level vs. Temperature
1.7
1.6

POR Voltage (V)

1.5
1.4
1.3
1.2
1.1
1
-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

Temperature

282

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.11 BOD Levels
Figure 27-24. BOD Voltage (2.7V level) vs. Temperature

2.8
2.79
2.78

Threshold (V)

2.77
2.76
2.75

Vcc Rise

2.74

Vcc Fall

2.73
2.72
2.71
2.7
2.69
-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

Temperature (C)Figure 27-25. BOD Voltage (2.9V level) vs. Temperature

3

2.98

Threshold (V)2.96

V c c Ris e
V c c Fall

2.94

2.92

2.9

2.88
-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

Temperature (C)2837707E–AVR–11/08

Figure 27-26. BOD Voltage (3.0V level) vs. Temperature

3.12
3.1

Threshold (V)3.08

Vcc Rise

3.06

Vcc Fall
3.04
3.02
3
2.98
-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

Temperature (C)Figure 27-27. BOD Voltage (3.5V level) vs. TemperatureBOD Voltage (3.0V level) vs.
Temperature

3.12
3.1

Threshold (V)3.08

Vcc Rise

3.06

Vcc Fall
3.04
3.02
3
2.98
-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

Temperature (C)284

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
Figure 27-28. BOD Voltage (3.6V level) vs. Temperature

3.58
3.69
3.57
3.68
3.56
3.67
3.55
3.66
Threshold (V)Threshold (V)

3.65
3.54

Vcc RiseVcc RiseVcc FallVcc Fall

3.64
3.53
3.63
3.52
3.62
3.51
3.61
3.5
3.6
3.49
3.59
3.48
3.58
-50
-40
-30
-20
-10
-50
-40
-30
-20
-10

0

0

10
20
30
40
10
20
30
40
Temperature (C)Temperature (C)

50
50

60
60

70
70

80
80

90
100
90
100

Figure 27-29. BOD Voltage (4.0V level) vs. Temperature

3.58
3.69
4.1
3.57
3.68
4.08
3.56
3.67

Threshold (V)ThresholdThreshold (V)
(V)

3.55
3.66
4.06
3.65
3.54
3.64
3.53
4.04
3.63
3.52

Vcc Rise
Vcc
VccRiseRise
Vcc FallVcc
VccFall
Fall

3.62
4.02
3.51
3.61
3.5
3.64
3.49
3.59
3.48
3.58
3.98
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
-50
00
10
20
30
40
50
60
70
80
90
-50 -40-40 -30-30 -20-20 -10
-10
10
20
30
40
50
60
70
80
90 100100
Temperature (C)Temperature
Temperature(C)(C)

285
7707E–AVR–11/08

Figure 27-30. BOD Voltage (4.3V level) vs. Temperature

3.58
3.69
4.1
4.42
3.57
3.68
4.4
4.08
3.56
3.67

Threshold (V)Threshold (V)Threshold (V)

3.55
3.66
4.38
4.06
3.65
3.54

Vcc Rise
Vcc
Vcc
VccRiseRise
Rise
Vcc FallVcc
Vcc
VccFall
Fall
Fall

4.36
3.64
3.53
4.04
3.63
3.524.34
3.62
4.02
3.51
4.32
3.61
3.5
3.64
3.49 4.3
3.59
3.48
3.58
3.98
4.28
-50
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
-50
000
10
-50
-40
-30
-20
-10
10
20
30
40
50
60
70
80
90
100
-50 -40-40 -30-30 -20-20 -10
-10
10 20
20 30
30 40
40 50
50 60
60 70
70 80
80 90
90 100100
Temperature (C)Temperature
Temperature(C)
Temperature(C)(C)

27.12 Watchdog Timer Frequency
Figure 27-31. WDT Oscillator Frequency vs. Vcc

128
126

FRC (kHz)

124

85

122

25
-40

120
118
116
114
2

2.5

3

3.5

4

4.5

5

5.5

V CC (V)286

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.13 Internal RC Oscillator Frequency
Figure 27-32. RC Oscillator Frequency vs. OSCCAL, T=25°C

20

FRC (MHz)

15

10

5

0
-1

15

31

47

63

79

95

111

127

143

159

175

191

207

223

239

255

OSCCAL (X1)

Figure 27-33. RC Oscillator Frequency vs. Vcc
8.7
8.6
8.5

FRC (MHz)

8.4

85°C

8.3

25°C

8.2

-40°C

8.1
8
7.9
7.8
7.7
2

2.5

3

3.5

4

4.5

5

5.5

V CC (V)287
7707E–AVR–11/08

28. Register Summary
Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(0xFF)

Reserved

-

-

-

-

-

-

-

-

288

(0xFE)

Reserved

-

-

-

-

-

-

-

-

(0xFD)

Reserved

-

-

-

-

-

-

-

-

(0xFC)

Reserved

-

-

-

-

-

-

-

-

(0xFB)

UPOE

UPWE1

UPWE0

UPDRV1UPDRV0

SCKI

DATAI

DPI

DMI

(0xFA)

PS2CON

-

-

-

-

-

-

-

PS2EN

(0xF9)

Reserved

-

-

-

-

-

-

-

-

(0xF8)

Reserved

-

-

-

-

-

-

-

-

(0xF7)

Reserved

-

-

-

-

-

-

-

-

(0xF6)

Reserved

-

-

-

-

-

-

-

-

(0xF5)

Reserved

-

-

-

-

-

-

-

-

(0xF4)

UEINT

-

-

(0xF3)

Reserved

-

-

-

-

-

(0xF2)UEBCLX(0xF1)UEDATX(0xF0)UEIENXFLERRENAKINE-NAKOUTERXSTPE

RXOUTESTALLEDE(0xEF)UESTA1X

-

-

-

-

-

CTRLDIROVERFIUNDERFI

-

-

Page

EPINT4:0-

BYCT7:0
DAT7:0(0xEE)UESTA0X

CFGOK(0xED)UECFG1X-(0xEC)UECFG0X(0xEB)UECONX-(0xEA)UERST-

DTSEQ1:0

EPSIZE2:0
EPTYPE1:0

NBUSYBK1:0

EPBK1:0

-

-

-

-

STALLRQ

STALLRQC

RSTDT

-

-

TXINE

CURRBK1:0
ALLOC

-

-

-

EPDIR

-

-

EPEN

EPRST4:0(0xE9)

UENUM

-

-

-

-

-

(0xE8)UEINTX

FIFOCON

NAKINIRWAL

NAKOUTIRXSTPIRXOUTISTALLEDIEPNUM2:0
TXINI(0xE7)

Reserved

-

-

-

-

-

-

-

-

(0xE6)

UDMFN

-

-

-

FNCERR----(0xE5)UDFNUMH

-

-

-

-

-

(0xE4)UDFNUML(0xE3)UDADDRADDEN(0xE2)UDIEN-

UPRSMEEORSME

WAKEUPEEORSTESOFE-(0xE1)UDINT-

UPRSMIEORSMI

WAKEUPIEORSTI

SOFI

-

SUSPI

(0xE0)

UDCON

-

-

-

-

-

RSTCPURMWKUP

DETACHFNUM10:8

FNUM7:0
UADD6:0SUSPE(0xDF)

Reserved

-

-

-

-

-

-

-

-

(0xDE)

Reserved

-

-

-

-

-

-

-

-

(0xDD)

Reserved

-

-

-

-

-

-

-

-

(0xDC)

Reserved

-

-

-

-

-

-

-

-

(0xDB)

Reserved

-

-

-

-

-

-

-

-

(0xDA)

Reserved

-

-

-

-

-

-

-

-

(0xD9)

Reserved

-

-

-

-

-

-

-

-

(0xD8)

USBCONUSBE-

FRZCLK

-

-

-

-

-

(0xD7)

Reserved

-

-

-

-

-

-

-

-

(0xD6)

Reserved

-

-

-

-

-

-

-

-

(0xD5)

Reserved

-

-

-

-

-

-

-

-

(0xD4)

Reserved

-

-

-

-

-

-

-

-

(0xD3)

Reserved

-

-

-

-

-

-

-

-

(0xD2)

CLKSTA

-

-

-

-

-

-

RCON

EXTON

(0xD1)

CLKSEL1

RCCKSEL3

RCCKSEL2

RCCKSEL1

RCCKSEL0

EXCKSEL3

EXCKSEL2

EXCKSEL1

EXCKSEL0(0xD0)

CLKSEL0

RCSUT1

RCSUT0

EXSUT1

EXSUT0

RCE

EXTE

-

CLKS

(0xCF)

Reserved

-

-

-

-

-

-

-

-

(0xCE)UDR1

USART1 I/O Data Register(0xCD)UBRR1H(0xCC)UBRR1L(0xCB)UCSR1D

-

-

-

-

-

-

CTSEN

RTSEN

(0xCA)UCSR1CUMSEL11

UMSEL10

UPM11

UPM10

USBS1

UCSZ11

UCSZ10UCPOL1(0xC9)UCSR1B

RXCIE1TXCIE1

UDRIE1

RXEN1

TXEN1

UCSZ12

RXB81

TXB81

(0xC8)UCSR1A

RXC1

TXC1

UDRE1

FE1

DOR1

PE1

U2X1

MPCM1

-

-

-

-

USART1 Baud Rate Register High Byte

USART1 Baud Rate Register Low Byte

(0xC7)

Reserved

-

-

-

-

-

-

-

-

(0xC6)

Reserved

-

-

-

-

-

-

-

-

(0xC5)

Reserved

-

-

-

-

-

-

-

-

(0xC4)

Reserved

-

-

-

-

-

-

-

-

(0xC3)

Reserved

-

-

-

-

-

-

-

-

(0xC2)

Reserved

-

-

-

-

-

-

-

-

(0xC1)

Reserved

-

-

-

-

-

-

-

-

(0xC0)

Reserved

-

-

-

-

-

-

-

-

(0xBF)

Reserved

-

-

-

-

-

-

-

-

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(0xBE)

Reserved

-

-

-

-

-

-

-

-

(0xBD)

Reserved

-

-

-

-

-

-

-

-

(0xBC)

Reserved

-

-

-

-

-

-

-

-

(0xBB)

Reserved

-

-

-

-

-

-

-

-

(0xBA)

Reserved

-

-

-

-

-

-

-

-

(0xB9)

Reserved

-

-

-

-

-

-

-

-

(0xB8)

Reserved

-

-

-

-

-

-

-

-

(0xB7)

Reserved

-

-

-

-

-

-

-

-

(0xB6)

Reserved

-

-

-

-

-

-

-

-

(0xB5)

Reserved

-

-

-

-

-

-

-

-

(0xB4)

Reserved

-

-

-

-

-

-

-

-

(0xB3)

Reserved

-

-

-

-

-

-

-

-

(0xB2)

Reserved

-

-

-

-

-

-

-

-

(0xB1)

Reserved

-

-

-

-

-

-

-

-

(0xB0)

Reserved

-

-

-

-

-

-

-

-

(0xAF)

Reserved

-

-

-

-

-

-

-

-

(0xAE)

Reserved

-

-

-

-

-

-

-

-

(0xAD)

Reserved

-

-

-

-

-

-

-

-

(0xAC)

Reserved

-

-

-

-

-

-

-

-

(0xAB)

Reserved

-

-

-

-

-

-

-

-

(0xAA)

Reserved

-

-

-

-

-

-

-

-

(0xA9)

Reserved

-

-

-

-

-

-

-

-

(0xA8)

Reserved

-

-

-

-

-

-

-

-

(0xA7)

Reserved

-

-

-

-

-

-

-

-

(0xA6)

Reserved

-

-

-

-

-

-

-

-

(0xA5)

Reserved

-

-

-

-

-

-

-

-

(0xA4)

Reserved

-

-

-

-

-

-

-

-

(0xA3)

Reserved

-

-

-

-

-

-

-

-

(0xA2)

Reserved

-

-

-

-

-

-

-

-

(0xA1)

Reserved

-

-

-

-

-

-

-

-

(0xA0)

Reserved

-

-

-

-

-

-

-

-

(0x9F)

Reserved

-

-

-

-

-

-

-

-

(0x9E)

Reserved

-

-

-

-

-

-

-

-

(0x9D)

Reserved

-

-

-

-

-

-

-

-

(0x9C)

Reserved

-

-

-

-

-

-

-

-

(0x9B)

Reserved

-

-

-

-

-

-

-

-

(0x9A)

Reserved

-

-

-

-

-

-

-

-

(0x99)

Reserved

-

-

-

-

-

-

-

-

(0x98)

Reserved

-

-

-

-

-

-

-

-

(0x97)

Reserved

-

-

-

-

-

-

-

-

(0x96)

Reserved

-

-

-

-

-

-

-

-

(0x95)

Reserved

-

-

-

-

-

-

-

-

(0x94)

Reserved

-

-

-

-

-

-

-

-

(0x93)

Reserved

-

-

-

-

-

-

-

-

(0x92)

Reserved

-

-

-

-

-

-

-

-

(0x91)

Reserved

-

-

-

-

-

-

-

-

(0x90)

Reserved

-

-

-

-

-

-

-

-

(0x8F)

Reserved

-

-

-

-

-

-

-

-

(0x8E)

Reserved

-

-

-

-

-

-

-

-

(0x8D)OCR1CH-

Page

Timer/Counter1 - Output Compare Register C High Byte

(0x8C)OCR1CLTimer/Counter1 - Output Compare Register C Low Byte

(0x8B)OCR1BH

Timer/Counter1 - Output Compare Register B High Byte

(0x8A)OCR1BLTimer/Counter1 - Output Compare Register B Low Byte

(0x89)OCR1AH

Timer/Counter1 - Output Compare Register A High Byte

(0x88)OCR1ALTimer/Counter1 - Output Compare Register A Low Byte

(0x87)ICR1H

Timer/Counter1 - Input Capture Register High Byte

(0x86)ICR1L

Timer/Counter1 - Input Capture Register Low Byte

(0x85)

TCNT1H

Timer/Counter1 - Counter Register High Byte

(0x84)

TCNT1L(0x83)

Reserved

-

-

-

-

-

-

-

(0x82)

TCCR1C

FOC1A

FOC1B

FOC1C

-

-

-

-

-

(0x81)

TCCR1B

ICNC1

ICES1

-

WGM13

WGM12

CS12

CS11

CS10

Timer/Counter1 - Counter Register Low Byte

(0x80)

TCCR1A

COM1A1

COM1A0COM1B1COM1B0

COM1C1

COM1C0

WGM11

WGM10

(0x7F)

Reserved

-

-

-

-

-

-

-

-

(0x7E)

Reserved

-

-

-

-

-

-

-

-

(0x7D)

Reserved

-

-

-

-

-

-

-

-

289
7707E–AVR–11/08

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(0x7C)

Reserved

-

-

-

-

-

-

-

-

(0x7B)

Reserved

-

-

-

-

-

-

-

-

(0x7A)

Reserved

-

-

-

-

-

-

-

-

(0x79)

Reserved

-

-

-

-

-

-

-

-

(0x78)

Reserved

-

-

-

-

-

-

-

-

(0x77)

Reserved

-

-

-

-

-

-

-

-

(0x76)

Reserved

-

-

-

-

-

-

-

-

(0x75)

Reserved

-

-

-

-

-

-

-

-

(0x74)

Reserved

-

-

-

-

-

-

-

-

(0x73)

Reserved

-

-

-

-

-

-

-

-

(0x72)

Reserved

-

-

-

-

-

-

-

-

(0x71)

Reserved

-

-

-

-

-

-

-

-

(0x70)

Reserved

-

-

-

-

-

-

-

-

(0x6F)TIMSK1

-

-

ICIE1

-

OCIE1COCIE1BOCIE1A

TOIE1
TOIE0

(0x6E)TIMSK0

-

-

-

-

-

OCIE0B

OCIE0A(0x6D)

Reserved

-

-

-

-

-

-

-

-

(0x6C)PCMSK1---

PCINT12PCINT11

PCINT10

PCINT9PCINT8(0x6B)PCMSK0PCINT7PCINT6

PCINT5

PCINT4

PCINT3

PCINT2

PCINT1

PCINT0(0x6A)

EICRB

ISC71

ISC70

ISC61

ISC60

ISC51

ISC50

ISC41

ISC40

(0x69)

EICRA

ISC31

ISC30

ISC21

ISC20

ISC11

ISC10

ISC01

ISC00

(0x68)

PCICR

-

-

-

-

-

-

PCIE1

PCIE0

(0x67)

Reserved

-

-

-

-

-

-

-

-

(0x66)OSCCALPRUSART1

Oscillator Calibration Register(0x65)

PRR1

PRUSB

-

-

-

-

-

-

(0x64)PRR0--

PRTIM0-PRTIM1

PRSPI

-

-

(0x63)

REGCR

-

-

-

-

-

-

-

REGDIS(0x62)WDTCKD----

WDEWIF

WDEWIEWCLKD1WCLKD0(0x61)

CLKPR

CLKPCE---CLKPS3

CLKPS2

CLKPS1

CLKPS0(0x60)WDTCSR

WDIF

WDIE

WDP3

WDCE

WDE

WDP2

WDP1

WDP0

0x3F (0x5F)

SREG

I

T

H

S

V

N

Z

C

0x3E (0x5E)

SPH

SP15

SP14

SP13

SP12

SP11

SP10

SP9

SP8

0x3D (0x5D)

SPL

SP7

SP6

SP5

SP4

SP3

SP2

SP1

SP0

0x3C (0x5C)

Reserved

-

-

-

-

-

-

-

-

0x3B (0x5B)

Reserved

-

-

-

-

-

-

-

-

0x3A (0x5A)

Reserved

-

-

-

-

-

-

-

-

0x39 (0x59)

Reserved

-

-

-

-

-

-

-

-

0x38 (0x58)

Reserved

-

-

-

-

-

-

-

-

0x37 (0x57)

SPMCSR

SPMIE

RWWSB

SIGRD

RWWSREBLBSET

PGWRT

PGERS

SPMEN

0x36 (0x56)

Reserved

-

-

-

-

-

-

-

-

0x35 (0x55)

MCUCR

-

-

-

-

-

-

IVSEL

IVCE

0x34 (0x54)

MCUSR

-

-

USBRF

-

WDRF

BORF

EXTRF

PORF

0x33 (0x53)

SMCR

-

-

-

-

SM2

SM1

SM0

SE

0x32 (0x52)

Reserved

-

-

-

-

-

-

-

-

0x31 (0x51)

DWDR

debugWIRE Data Register0x30 (0x50)

ACSR

ACD

ACBG

ACO

ACI

ACIE

ACIC

ACIS1

ACIS0

0x2F (0x4F)

Reserved

-

-

-

-

-

-

-

-

0x2E (0x4E)

SPDR

SPI Data Register

0x2D (0x4D)

SPSR

SPIF

WCOL

-

-

-

-

-

SPI2X

0x2C (0x4C)

SPCR

SPIE

SPE

DORD

MSTR

CPOL

CPHA

SPR1

SPR0

0x2B (0x4B)

GPIOR2

PLLP0

PLLE

PLOCK

General Purpose I/O Register 2

0x2A (0x4A)

GPIOR10x29 (0x49)

PLLCSR

0x28 (0x48)

OCR0B

Timer/Counter0 Output Compare Register B

0x27 (0x47)

OCR0A

Timer/Counter0 Output Compare Register A

0x26 (0x46)

TCNT0

0x25 (0x45)

TCCR0B

FOC0A

FOC0B

-

-

WGM02

CS02

CS01

CS00

0x24 (0x44)

TCCR0A

COM0A1

COM0A0COM0B1COM0B0

-

-

WGM01

WGM00

0x23 (0x43)

GTCCR

TSM

-

-

-

-

-

PSRASYPSRSYNC

0x22 (0x42)

EEARH

-

-

-

-

0x21 (0x41)

EEARL

0x20 (0x40)

EEDR

0x1F (0x3F)

EECR

0x1E (0x3E)

GPIOR0General Purpose I/O Register 1
-

-

-

PLLP2

PLLP1

Timer/Counter0 (8 Bit)

EEPROM Address Register High Byte

EEPROM Address Register Low Byte
EEPROM Data Register
-

-

EEPM1

EEPM0

EERIE

EEMPE

EEPE

EERE

General Purpose I/O Register 0

0x1D (0x3D)

EIMSK

INT7

INT6

INT5

INT4

INT3

INT2

INT1

INT0

0x1C (0x3C)

EIFR

INTF7

INTF6

INTF5

INTF4

INTF3

INTF2

INTF1

INTF0

0x1B (0x3B)

PCIFR

-

-

-

-

-

-

PCIF1

PCIF0

290

Page

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

0x1A (0x3A)

Reserved

-

-

-

-

-

-

-

-

0x19 (0x39)

Reserved

-

-

-

-

-

-

-

-

0x18 (0x38)

Reserved

-

-

-

-

-

-

-

-

0x17 (0x37)

Reserved

-

-

-

-

-

-

-

-

0x16 (0x36)

TIFR1

-

-

ICF1

-

OCF1C

OCF1B

OCF1A

TOV1

0x15 (0x35)

TIFR0

-

-

-

-

-

OCF0B

OCF0A

TOV0

0x14 (0x34)

Reserved

-

-

-

-

-

-

-

-

0x13 (0x33)

Reserved

-

-

-

-

-

-

-

-

0x12 (0x32)

Reserved

-

-

-

-

-

-

-

-

0x11 (0x31)

Reserved

-

-

-

-

-

-

-

-

0x10 (0x30)

Reserved

-

-

-

-

-

-

-

-

0x0F (0x2F)

Reserved

-

-

-

-

-

-

-

-

0x0E (0x2E)

Reserved

-

-

-

-

-

-

-

-

0x0D (0x2D)

Reserved

-

-

-

-

-

-

-

-

0x0C (0x2C)

Reserved

-

-

-

-

-

-

-

-

0x0B (0x2B)

PORTD

PORTD7

PORTD6

PORTD5PORTD4PORTD3PORTD2PORTD1PORTD00x0A (0x2A)

DDRD

DDD7

DDD6

DDD5

DDD4

DDD3

DDD2

DDD1

DDD0

0x09 (0x29)

PIND

PIND7

PIND6

PIND5

PIND4

PIND3

PIND2

PIND1

PIND0

0x08 (0x28)

PORTC

PORTC7PORTC6PORTC5PORTC4-PORTC2PORTC1PORTC00x07 (0x27)

DDRC

DDC7

DDC6

DDC5

DDC4

-

DDC2

DDC1

DDC0

0x06 (0x26)

PINC

PINC7

PINC6

PINC5

PINC4

-

PINC2

PINC1

PINC0

0x05 (0x25)

PORTB

PORTB7PORTB6PORTB5PORTB4PORTB3PORTB2PORTB1PORTB00x04 (0x24)

DDRB

DDB7

DDB6

DDB5

DDB4

DDB3

DDB2

DDB1

DDB0

0x03 (0x23)

PINB

PINB7

PINB6

PINB5

PINB4

PINB3

PINB2

PINB1

PINB0

0x02 (0x22)

Reserved

-

-

-

-

-

-

-

-

0x01 (0x21)

Reserved

-

-

-

-

-

-

-

-

0x00 (0x20)

Reserved

-

-

-

-

-

-

-

-

Note:

Page

1. For compatibility with future devices, reserved bits should be written to zero if accessed. Moreover reserved bits are notguaranteed to be read as “0”. Reserved I/O memory addresses should never be written.
2. I/O registers within the address range $00 - $1F are directly bit-accessible using the SBI and CBI instructions. In these registers, the value of single bits can be checked by using the SBIS and SBIC instructions.
3. Some of the status flags are cleared by writing a logical one to them. Note that the CBI and SBI instructions will operate on
all bits in the I/O register, writing a one back into any flag read as set, thus clearing the flag. The CBI and SBI instructions
work with registers 0x00 to 0x1F only.
4. When using the I/O specific commands IN and OUT, the I/O addresses $00 - $3F must be used. When addressing I/O registers as data space using LD and ST instructions, $20 must be added to these addresses. The AT90USB82/162 is acomplex microcontroller with more peripheral units than can be supported within the 64 location reserved in Opcode for the
IN and OUT instructions. For the Extended I/O space from $60 - $1FF in SRAM, only the ST/STS/STD and LD/LDS/LDD
instructions can be used.

291
7707E–AVR–11/08

29. Instruction Set Summary
Mnemonics

Operands

Description

Operation

Flags#Clocks
1

ARITHMETIC AND LOGIC INSTRUCTIONS
ADD

Rd, Rr

Add two Registers

Rd ← Rd + Rr

Z,C,N,V,H

ADC

Rd, Rr

Add with Carry two Registers

Rd ← Rd + Rr + C

Z,C,N,V,H

1

ADIW

Rdl,K

Add Immediate to Word

Rdh:Rdl ← Rdh:Rdl + K

Z,C,N,V,S

2

SUB

Rd, Rr

Subtract two Registers

Rd ← Rd - Rr

Z,C,N,V,H

1

SUBI

Rd, K

Subtract Constant from Register

Rd ← Rd - K

Z,C,N,V,H

1

SBC

Rd, Rr

Subtract with Carry two Registers

Rd ← Rd - Rr - C

Z,C,N,V,H

1

SBCI

Rd, K

Subtract with Carry Constant from Reg.

Rd ← Rd - K - C

Z,C,N,V,H

1

SBIW

Rdl,K

Subtract Immediate from Word

Rdh:Rdl ← Rdh:Rdl - K

Z,C,N,V,S

2

AND

Rd, Rr

Logical AND Registers

Rd ← Rd • Rr

Z,N,V

1

ANDI

Rd, K

Logical AND Register and Constant

Rd ← Rd • K

Z,N,V

1

OR

Rd, Rr

Logical OR Registers

Rd ← Rd v Rr

Z,N,V

1

ORI

Rd, K

Logical OR Register and Constant

Rd ← Rd v K

Z,N,V

1

EOR

Rd, Rr

Exclusive OR Registers

Rd ← Rd ⊕ Rr

Z,N,V

1

COM

Rd

One’s Complement

Rd ← 0xFF − Rd

Z,C,N,V

1

NEG

Rd

Two’s Complement

Rd ← 0x00 − Rd

Z,C,N,V,H

1

SBR

Rd,K

Set Bit(s) in Register

Rd ← Rd v K

Z,N,V

1

CBR

Rd,K

Clear Bit(s) in Register

Rd ← Rd • (0xFF - K)

Z,N,V

1

INC

Rd

Increment

Rd ← Rd + 1

Z,N,V

1
1

DEC

Rd

Decrement

Rd ← Rd − 1

Z,N,V

TST

Rd

Test for Zero or Minus

Rd ← Rd • Rd

Z,N,V

1

CLR

Rd

Clear Register

Rd ← Rd ⊕ Rd

Z,N,V

1

SER

Rd

Set Register

Rd ← 0xFF

None

1

Relative Jump

PC ← PC + k + 1

None

2

Indirect Jump to (Z)PC ← Z

None

2
3

BRANCH INSTRUCTIONS
RJMP

k

IJMP
JMP

k

Direct Jump

PC ← k

None

RCALL

k

Relative Subroutine Call

PC ← PC + k + 1

None

4

Indirect Call to (Z)PC ← Z

None

4

ICALL
CALL

k

RET
RETI
CPSE

Rd,Rr

Direct Subroutine Call

PC ← kNone

5

Subroutine Return

PC ← STACK

None

5

Interrupt Return

PC ← STACK

I

5

Compare, Skip if Equal

if (Rd = Rr) PC ← PC + 2 or 3

None

1/2/3

CP

Rd,Rr

CompareRd − Rr

Z, N,V,C,H

1

CPC

Rd,Rr

Compare with CarryRd − Rr − C

Z, N,V,C,H

1

CPI

Rd,K

Compare Register with Immediate

Rd − K

Z, N,V,C,H

1

SBRC

Rr, b

Skip if Bit in Register Cleared

if (Rr(b)=0) PC ← PC + 2 or 3

None

1/2/3

SBRS

Rr, b

Skip if Bit in Register is Set

if (Rr(b)=1) PC ← PC + 2 or 3

None

1/2/3

SBIC

P, b

Skip if Bit in I/O Register Cleared

if (P(b)=0) PC ← PC + 2 or 3

None

1/2/3

SBIS

P, b

Skip if Bit in I/O Register is Set

if (P(b)=1) PC ← PC + 2 or 3

None

1/2/3

BRBS

s, k

Branch if Status Flag Set

if (SREG(s) = 1) then PC←PC+k + 1

None

1/2

BRBC

s, k

Branch if Status Flag Cleared

if (SREG(s) = 0) then PC←PC+k + 1

None

1/2

BREQ

k

Branch if Equal

if (Z = 1) then PC ← PC + k + 1

None

1/2

BRNE

k

Branch if Not Equal

if (Z = 0) then PC ← PC + k + 1

None

1/2

BRCS

k

Branch if Carry Set

if (C = 1) then PC ← PC + k + 1

None

1/2

BRCC

k

Branch if Carry Cleared

if (C = 0) then PC ← PC + k + 1

None

1/2

BRSH

k

Branch if Same or Higher

if (C = 0) then PC ← PC + k + 1

None

1/2

BRLO

k

Branch if Lower

if (C = 1) then PC ← PC + k + 1

None

1/2

BRMI

k

Branch if Minus

if (N = 1) then PC ← PC + k + 1

None

1/2

BRPL

k

Branch if Plus

if (N = 0) then PC ← PC + k + 1

None

1/2

BRGE

k

Branch if Greater or Equal, Signed

if (N ⊕ V= 0) then PC ← PC + k + 1

None

1/2

BRLT

k

Branch if Less Than Zero, Signed

if (N ⊕ V= 1) then PC ← PC + k + 1

None

1/2

BRHS

k

Branch if Half Carry Flag Set

if (H = 1) then PC ← PC + k + 1

None

1/2

BRHC

k

Branch if Half Carry Flag Clearedif (H = 0) then PC ← PC + k + 1

None

1/2
1/2

BRTS

k

Branch if T Flag Set

if (T = 1) then PC ← PC + k + 1

None

BRTC

k

Branch if T Flag Cleared

if (T = 0) then PC ← PC + k + 1

None

1/2

BRVS

k

Branch if Overflow Flag is Set

if (V = 1) then PC ← PC + k + 1

None

1/2

BRVC

k

Branch if Overflow Flag is Cleared

if (V = 0) then PC ← PC + k + 1

None

1/2

BRIE

k

Branch if Interrupt Enabledif ( I = 1) then PC ← PC + k + 1

None

1/2

BRID

k

Branch if Interrupt Disabledif ( I = 0) then PC ← PC + k + 1

None

1/2

BIT AND BIT-TEST INSTRUCTIONS

292

SBI

P,b

Set Bit in I/O Register

I/O(P,b) ← 1

None

2

CBI

P,b

Clear Bit in I/O Register

I/O(P,b) ← 0

None

2

LSL

Rd

Logical Shift Left

Rd(n+1) ← Rd(n), Rd(0) ← 0

Z,C,N,V

1

LSR

Rd

Logical Shift Right

Rd(n) ← Rd(n+1), Rd(7) ← 0

Z,C,N,V

1

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AT90USB82/162
Mnemonics

Operands

Description

Operation

Flags

ROL

Rd

Rotate Left Through Carry

Rd(0)←C,Rd(n+1)← Rd(n),C←Rd(7)Z,C,N,V#Clocks
1

ROR

Rd

Rotate Right Through Carry

Rd(7)←C,Rd(n)← Rd(n+1),C←Rd(0)Z,C,N,V

1
1

ASR

Rd

Arithmetic Shift Right

Rd(n) ← Rd(n+1), n=0..6

Z,C,N,V

SWAP

Rd

Swap Nibbles

Rd(3..0)←Rd(7..4),Rd(7..4)←Rd(3..0)

None

1

BSET

s

Flag Set

SREG(s) ← 1

SREG(s)

1
1

BCLR

s

Flag Clear

SREG(s) ← 0

SREG(s)

BST

Rr, b

Bit Store from Register to T

T ← Rr(b)

T

1

BLD

Rd, b

Bit load from T to Register

Rd(b) ← T

None

1

SEC

Set Carry

C←1

C

1

CLC

Clear Carry

C←0

C

1

SEN

Set Negative Flag

N←1

N

1

CLN

Clear Negative Flag

N←0

N

1

SEZ

Set Zero Flag

Z←1

Z

1

CLZ

Clear Zero Flag

Z←0

Z

1

SEI

Global Interrupt Enable

I←1

I

1

CLI

Global Interrupt Disable

I←0

I

1

SES

Set Signed Test Flag

S←1

S

1

CLS

Clear Signed Test Flag

S←0

S

1

SEV

Set Twos Complement Overflow.

V←1

V

1

CLV

Clear Twos Complement Overflow

V←0

V

1

SET

Set T in SREG

T←1

T

1

CLT

Clear T in SREG

T←0

T

1

SEH
CLH

Set Half Carry Flag in SREG
Clear Half Carry Flag in SREG

H←1
H←0

H
H

1
1

Rd ← Rr
Rd+1:Rd ← Rr+1:Rr

None

1

None

1
1

DATA TRANSFER INSTRUCTIONS
MOV

Rd, RrMove Between Registers

MOVW

Rd, RrCopy Register Word

LDI

Rd, K

Load Immediate

Rd ← K

None

LD

Rd, X

Load Indirect

Rd ← (X)

None

2

LD

Rd, X+

Load Indirect and Post-Inc.

Rd ← (X), X ← X + 1

None

2
2

LD

Rd, - X

Load Indirect and Pre-Dec.

X ← X - 1, Rd ← (X)

None

LD

Rd, Y

Load Indirect

Rd ← (Y)

None

2

LD

Rd, Y+

Load Indirect and Post-Inc.

Rd ← (Y), Y ← Y + 1

None

2

LD

Rd, - Y

Load Indirect and Pre-Dec.

Y ← Y - 1, Rd ← (Y)

None

2

LDD

Rd,Y+qLoad Indirect with Displacement

Rd ← (Y + q)

None

2
2

LD

Rd, Z

Load Indirect

Rd ← (Z)NoneLD

Rd, Z+

Load Indirect and Post-Inc.

Rd ← (Z), Z ← Z+1

None

2

LD

Rd, -Z

Load Indirect and Pre-Dec.

Z ← Z - 1, Rd ← (Z)

None

2

LDD

Rd, Z+q

Load Indirect with Displacement

Rd ← (Z + q)

None

2

LDS

Rd, k

Load Direct from SRAM

Rd ← (k)

None

2

ST

X, Rr

Store Indirect(X) ← Rr

None

2

ST

X+, RrStore Indirect and Post-Inc.

(X) ← Rr, X ← X + 1

None

2

ST

- X, Rr

Store Indirect and Pre-Dec.

X ← X - 1, (X) ← Rr

None

2

ST

Y, Rr

Store Indirect(Y) ← Rr

None

2

ST

Y+, RrStore Indirect and Post-Inc.

(Y) ← Rr, Y ← Y + 1

None

2

ST

- Y, Rr

Store Indirect and Pre-Dec.

Y ← Y - 1, (Y) ← Rr

None

2

STD

Y+q,RrStore Indirect with Displacement(Y + q) ← Rr

None

2

ST

Z, Rr

Store Indirect(Z) ← Rr

None

2

ST

Z+, RrStore Indirect and Post-Inc.

(Z) ← Rr, Z ← Z + 1

None

2

ST

-Z, RrStore Indirect and Pre-Dec.

Z ← Z - 1, (Z) ← Rr

None

2

STD

Z+q,RrStore Indirect with Displacement(Z + q) ← Rr

None

2

STS

k, Rr

LPM

Store Direct to SRAM(k) ← Rr

None

2

Load Program Memory

R0 ← (Z)

None

3

LPM

Rd, Z

Load Program Memory

Rd ← (Z)

None

3

LPM

Rd, Z+

Load Program Memory and Post-Inc

Rd ← (Z), Z ← Z+1

None

3

Store Program Memory(Z) ← R1:R0

None

-

In PortRd ← P

None

1

SPM
IN

Rd, P

OUT

P, Rr

Out Port

P ← Rr

None

1

PUSH

Rr

Push Register on Stack

STACK ← Rr

None

2

POP

Rd

Pop Register from Stack

Rd ← STACK

None

2

MCU CONTROL INSTRUCTIONSNOPNo Operation

None

1

SLEEP

Sleep

(see specific descr. for Sleep function)

None

1

WDR
BREAK

Watchdog Reset
Break(see specific descr. for WDR/timer)
For On-chip Debug Only

None
None

1
N/A

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30. Ordering Information

Part Number

Temp. Range

90USB82-16MU

Industrial Green

Flash Memory Size
8K

Package
QFN32

Product Marking
90USB82-16MU

90USB162-16MU

Industrial Green

16K

QFN32

90USB162-16MU

90USB162-16AU

Industrial Green

16K

TQFP3290USB162-16AU

31. Packaging Information
Package Type
QFN32

PN, 32-Lead 5.0 x 5.0 mm Body, 0.50 mm Pitch
Quad Flat No Lead Package (QFN)

TQFP32MA, 32-Lead 7 x 7 mm Body size, 1.00 mm Bodu Thickness
0.8 mm Lead Pitch, Thin Profile Plastic Quad Flat Package (TQFP)
Note:
If ultrasonic process is used for assembly, we recommend that frequency to be applied should be either below or
above the 12 to 26kHz range.

294

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AT90USB82/162
31.1

QFN32

295
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31.2

296

TQFP32

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7707E–AVR–11/08

AT90USB82/162
32. Errata
32.1

AT90USB162 Errata History
Silicon

QFP32

QFN32

Release‘DateCode LotNumber’ marking‘DateCode LotNumber’ marking

First Release‘0709 J4973-2’‘0705 6J4972’‘0709 J5597-1’

all lots marked
90USB162–16MES‘0714 50-2’

Second Release‘0709 F3150-1’‘0722 50-3’‘0735 3151’

Third Release

32.1.1All date codes after 0709

All other lots

AT90USB162 First Release
1. High current consumption in sleep mode
If a pending interrupt cannot wake the part up from the selected mode, the current consumption will increase during sleep when executing the SLEEP instruction directly after a SEI
instruction.
Problem Fix/workaround
Before entering sleep, interrupts not used to wake up the part from the sleep mode should
be disabled.
2. PS2 high level clamped to UCAP
When configured in PS2 mode, the output high level is clamped to the UCAP voltage level.
Problem Fix/workaround
None.
3. Transient perturbation in USB suspend mode generates overconsumption
In device mode and when the USB is suspended, transient perturbation received on the
USB lines generates a wake up state. However the idle state following the perturbation does
not set the SUSPI bit anymore. The internal USB engine remains in suspend mode but theUSB differential receiver is still enabled and generates a typical 300µA extra-power consumption. Detection of the suspend state after the transient perturbation should be
performed by software (instead of reading the SUSPI bit).
Problem fix/workaroundUSB waiver allows bus powered devices to consume up to 2.5mA in suspend state.

32.1.2

AT90USB162 Second Release
1. High current consumption in sleep mode
If a pending interrupt cannot wake the part up from the selected mode, the current consumption will increase during sleep when executing the SLEEP instruction directly after a SEI
instruction.
Problem Fix/workaround

297
7707E–AVR–11/08

Before entering sleep, interrupts not used to wake up the part from the sleep mode should
be disabled.

2. Extra power consumption
The typical power comsumption is increased by 90µA at 5V and by 160µA in worst caseconditions.
Problem Fix/workaround
None.
3. Transient perturbation in USB suspend mode generates overconsumption
In device mode and when the USB is suspended, transient perturbation received on the
USB lines generates a wake up state. However the idle state following the perturbation does
not set the SUSPI bit anymore. The internal USB engine remains in suspend mode but theUSB differential receiver is still enabled and generates a typical 300µA extra-power consumption. Detection of the suspend state after the transient perturbation should be
performed by software (instead of reading the SUSPI bit).
Problem fix/workaroundUSB waiver allows bus powered devices to consume up to 2.5mA in suspend state.
32.1.3

AT90USB162 Third Release
1. High current consumption in sleep mode
If a pending interrupt cannot wake the part up from the selected mode, the current consumption will increase during sleep when executing the SLEEP instruction directly after a SEI
instruction.
Problem Fix/workaround
Before entering sleep, interrupts not used to wake up the part from the sleep mode should
be disabled.
2. Transient perturbation in USB suspend mode generates overconsumption
In device mode and when the USB is suspended, transient perturbation received on the
USB lines generates a wake up state. However the idle state following the perturbation does
not set the SUSPI bit anymore. The internal USB engine remains in suspend mode but theUSB differential receiver is still enabled and generates a typical 300µA extra-power consumption. Detection of the suspend state after the transient perturbation should be
performed by software (instead of reading the SUSPI bit).
Problem fix/workaroundUSB waiver allows bus powered devices to consume up to 2.5mA in suspend state.

32.2
32.2.1

AT90USB82 Errata History
AT90USB82 Initial Release (all lots)
1. High current consumption in sleep mode
If a pending interrupt cannot wake the part up from the selected mode, the current consumption will increase during sleep when executing the SLEEP instruction directly after a SEI
instruction.

298

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AT90USB82/162
Problem Fix/workaround
Before entering sleep, interrupts not used to wake up the part from the sleep mode should
be disabled.
2. Transient perturbation in USB suspend mode generates overconsumption
In device mode and when the USB is suspended, transient perturbation received on the
USB lines generates a wake up state. However the idle state following the perturbation does
not set the SUSPI bit anymore. The internal USB engine remains in suspend mode but theUSB differential receiver is still enabled and generates a typical 300µA extra-power consumption. Detection of the suspend state after the transient perturbation should be
performed by software (instead of reading the SUSPI bit).
Problem fix/workaroundUSB waiver allows bus powered devices to consume up to 2.5mA in suspend state.

33. Datasheet Revision History for AT90USB82/162
Please note that the referring page numbers in this section are referred to this document. The
referring revision in this section are referring to the document revision.

33.1

Changes from 7707A to 7707B
1. Removed all references to Timer/Counter 2, A/D Converter.
2. Clarified information in Power Reduction Mode and Timer/Counter 1 sections.
3. Added USB design guidelines and schematics.
4. Updated default fuse configuration & EEPROM page size.
5. Updated AC/DC parameters.
6. Updated Errata section.

33.2

Changes from 7707B to 7707C
1. Updated Errata section.

33.3

Changes from 7707C to 7707D
1. Correction to Oscillator description, page 245.

33.4

Changes from 7707D to 7707E
1. Updated package descriptions.
2. Added recomendation for ultrasonic assembly.
3. Updated typical self powered applications.

299
7707E–AVR–11/08

Features ..................................................................................................... 1
1

Pin Configurations ................................................................................... 3
1.1 Disclaimer ................................................................................................................3

2

Overview ................................................................................................... 4
2.1 Block Diagram .........................................................................................................4
2.2 Pin Descriptions .......................................................................................................5

3

About Code Examples ............................................................................. 7

4

AVR CPU Core .......................................................................................... 8
4.1 Introduction ..............................................................................................................8
4.2 Architectural Overview .............................................................................................8
4.3 ALU – Arithmetic Logic Unit .....................................................................................9
4.4 Status Register ........................................................................................................9
4.5 General Purpose Register File ..............................................................................11
4.6 Stack Pointer .........................................................................................................12
4.7 Instruction Execution Timing .................................................................................12
4.8 Reset and Interrupt Handling .................................................................................13

5

AVR AT90USB82/162 Memories ........................................................... 16
5.1 In-System Reprogrammable Flash Program Memory ...........................................16
5.2 SRAM Data Memory ..............................................................................................17
5.3 EEPROM Data Memory ........................................................................................18
5.4 I/O Memory ............................................................................................................24

6

System Clock and Clock Options ......................................................... 25
6.1 Clock Systems and their Distribution .....................................................................25
6.2 Clock Switch ..........................................................................................................26
6.3 Clock Sources .......................................................................................................29
6.4 Low Power Crystal Oscillator .................................................................................30
6.5 Calibrated Internal RC Oscillator ...........................................................................32
6.6 External Clock .......................................................................................................34
6.7 Clock Output Buffer ...............................................................................................34
6.8 System Clock Prescaler ........................................................................................34
6.9 PLL ........................................................................................................................36

7

Power Distribution ................................................................................. 398Power Management and Sleep Modes ................................................. 41

1

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AT90USB82/162
8.1 Idle Mode ...............................................................................................................42
8.2 Power-down Mode .................................................................................................42
8.3 Power-save Mode ..................................................................................................42
8.4 Standby Mode .......................................................................................................42
8.5 Extended Standby Mode .......................................................................................42
8.6 Power Reduction Register .....................................................................................43
8.7 Minimizing Power Consumption ............................................................................44

9

System Control and Reset .................................................................... 46
9.1 Resetting the AVR .................................................................................................46
9.2 Reset Sources .......................................................................................................46
9.3 Power-on Reset .....................................................................................................47
9.4 External Reset .......................................................................................................48
9.5 Brown-out Detection ..............................................................................................49
9.6 Watchdog Reset ....................................................................................................50
9.7 USB Reset .............................................................................................................50
9.8 Internal Voltage Reference ....................................................................................52
9.9 Watchdog Timer ....................................................................................................52

10 Interrupts ................................................................................................ 63
10.1 Interrupt Vectors in AT90USB82/162 ..................................................................63

11 I/O-Ports .................................................................................................. 67
11.1 Introduction ..........................................................................................................67
11.2 Ports as General Digital I/O .................................................................................68
11.3 Alternate Port Functions ......................................................................................72
11.4 Register Description for I/O-Ports ........................................................................82

12 External Interrupts ................................................................................. 84
13 Timer/Counter0 and Timer/Counter1 Prescalers ................................ 88
14 8-bit Timer/Counter0 with PWM ............................................................ 90
14.1 Overview ..............................................................................................................90
14.2 Timer/Counter Clock Sources .............................................................................91
14.3 Counter Unit ........................................................................................................91
14.4 Output Compare Unit ...........................................................................................92
14.5 Compare Match Output Unit ................................................................................94
14.6 Modes of Operation .............................................................................................95
14.7 Timer/Counter Timing Diagrams .........................................................................9927707E–AVR–11/08

14.8 8-bit Timer/Counter Register Description ..........................................................100

15 16-bit Timer/Counter 1 with PWM ....................................................... 107
15.1 Overview ............................................................................................................107
15.2 Accessing 16-bit Registers ................................................................................109
15.3 Timer/Counter Clock Sources ...........................................................................112
15.4 Counter Unit ......................................................................................................113
15.5 Input Capture Unit .............................................................................................114
15.6 Output Compare Units .......................................................................................116
15.7 Compare Match Output Unit ..............................................................................118
15.8 Modes of Operation ...........................................................................................119
15.9 Timer/Counter Timing Diagrams .......................................................................126
15.10 16-bit Timer/Counter Register Description ......................................................128

16 Serial Peripheral Interface – SPI ......................................................... 137
16.1 SS Pin Functionality ..........................................................................................141
16.2 Data Modes .......................................................................................................144

17 USART ................................................................................................... 146
17.1 Overview ............................................................................................................146
17.2 Clock Generation ...............................................................................................147
17.3 Frame Formats ..................................................................................................150
17.4 USART Initialization ...........................................................................................152
17.5 Data Transmission – The USART Transmitter ..................................................153
17.6 Data Reception – The USART Receiver ...........................................................155
17.7 Asynchronous Data Reception ..........................................................................159
17.8 Multi-processor Communication Mode ..............................................................162
17.9 Hardware Flow Control ......................................................................................163
17.10 USART Register Description ...........................................................................165
17.11 Examples of Baud Rate Setting .......................................................................169

18 USART in SPI Mode ............................................................................. 173
18.1 Overview ............................................................................................................173
18.2 Clock Generation ...............................................................................................174
18.3 SPI Data Modes and Timing ..............................................................................175
18.4 Frame Formats ..................................................................................................175
18.5 Data Transfer .....................................................................................................177
18.6 USART MSPIM Register Description ................................................................179
18.7 AVR USART MSPIM vs.

3

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AT90USB82/162
AVR SPI 181

19 USB controller ...................................................................................... 183
19.1 Features ............................................................................................................183
19.2 Block Diagram ...................................................................................................183
19.3 Typical Application Implementation ...................................................................184
19.4 General Operating Modes .................................................................................187
19.5 Power modes .....................................................................................................190
19.6 Memory management ........................................................................................190
19.7 PAD suspend .....................................................................................................191
19.8 D+/D- Read/write ...............................................................................................192
19.9 Registers description .........................................................................................193
19.10 USB Software Operating modes .....................................................................194

20 USB Device Operating modes ............................................................ 196
20.1 Introduction ........................................................................................................196
20.2 Power-on and reset ...........................................................................................196
20.3 Endpoint reset ...................................................................................................196
20.4 USB reset ..........................................................................................................197
20.5 Endpoint selection .............................................................................................197
20.6 Endpoint activation ............................................................................................197
20.7 Address Setup ...................................................................................................198
20.8 Suspend, Wake-up and Resume .......................................................................199
20.9 Detach ...............................................................................................................199
20.10 Remote Wake-up .............................................................................................200
20.11 STALL request .................................................................................................200
20.12 CONTROL endpoint management ..................................................................201
20.13 OUT endpoint management ............................................................................202
20.14 IN endpoint management ................................................................................20420.15 Isochronous mode ...........................................................................................206
20.16 Overflow ..........................................................................................................206
20.17 Interrupts .........................................................................................................207
20.18 Registers .........................................................................................................208

21 PS/2 ....................................................................................................... 220
21.1 Characteristics ...................................................................................................220

22 Analog Comparator .............................................................................. 223

47707E–AVR–11/08

23 Boot Loader Support – Read-While-Write Self-Programming ......... 225
23.1 Boot Loader Features ........................................................................................225
23.2 Application and Boot Loader Flash Sections .....................................................225
23.3 Read-While-Write and No Read-While-Write Flash Sections ............................225
23.4 Boot Loader Lock Bits .......................................................................................228
23.5 Entering the Boot Loader Program ....................................................................229
23.6 Addressing the Flash During Self-Programming ...............................................233
23.7 Self-Programming the Flash ..............................................................................233

24 debugWIRE On-chip Debug System .................................................. 241
24.1 Features ............................................................................................................24124.2 Overview ............................................................................................................24124.3 Physical Interface ..............................................................................................24124.4 Software Break Points .......................................................................................242
24.5 Limitations of debugWIRE .................................................................................242
24.6 debugWIRE Related Register in I/O Memory ....................................................242

25 Memory Programming ......................................................................... 243
25.1 Program And Data Memory Lock Bits ...............................................................243
25.2 Fuse Bits ............................................................................................................244
25.3 Signature Bytes .................................................................................................246
25.4 Calibration Byte .................................................................................................246
25.5 Parallel Programming Parameters, Pin Mapping, and Commands ...................246
25.6 Parallel Programming ........................................................................................249
25.7 Serial Downloading ............................................................................................257
25.8 Serial Programming Pin Mapping ......................................................................257

26 Electrical Characteristics .................................................................... 262
26.1 Absolute Maximum Ratings* .............................................................................262
26.2 DC Characteristics .............................................................................................262
26.3 External Clock Drive Waveforms .......................................................................26426.4 External Clock Drive ..........................................................................................26426.5 Maximum speed vs. VCC ...........................................................................................................................26526.6 SPI Timing Characteristics ................................................................................26526.7 Hardware Boot EntranceTiming Characteristics ................................................266

27 AT90USB82/162 Typical Characteristics – Preliminary Data ........... 268
27.1 Input Voltage Levels ..........................................................................................269
27.2 Output Voltage Levels .......................................................................................271

5

AT90USB82/162

7707E–AVR–11/08

AT90USB82/162
27.3 I/O Pull-up Current .............................................................................................274
27.4 Power-down Supply Current ..............................................................................275
27.5 Idle Supply Current ............................................................................................278
27.6 Active Supply Current ........................................................................................279
27.7 Reset Supply Current ........................................................................................279
27.8 Bandgap Voltage ...............................................................................................280
27.9 USB Regulator ...................................................................................................281
27.10 Power-On Reset ..............................................................................................282
27.11 BOD Levels .....................................................................................................283
27.12 Watchdog Timer Frequency ............................................................................286
27.13 Internal RC Oscillator Frequency ....................................................................287

28 Register Summary ............................................................................... 288
29 Instruction Set Summary ..................................................................... 292
30 Ordering Information ........................................................................... 294
31 Packaging Information ........................................................................ 294
31.1 QFN32 ...............................................................................................................295
31.2 TQFP32 .............................................................................................................296

32 Errata ..................................................................................................... 297
32.1 AT90USB162 Errata History ..............................................................................297
32.2 AT90USB82 Errata History ................................................................................298

33 Datasheet Revision History for AT90USB82/162 .............................. 299
33.1 Changes from 7707A to 7707B .........................................................................299
33.2 Changes from 7707B to 7707C .........................................................................299
33.3 Changes from 7707C to 7707D .........................................................................299
33.4 Changes from 7707D to 7707E .........................................................................299

67707E–AVR–11/08

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7707E–AVR–11/08