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Nexys Video™ FPGA Board Reference Manual
Revised June 17, 2015
This manual applies to the Nexys Video rev. A

Table of Contents
Table of Contents .................................................................................................................. 1
Overview............................................................................................................................... 3
Regulatory Warning............................................................................................................... 5
1

Power Supplies .............................................................................................................. 5

2

FPGA Configuration ........................................................................................................ 73

2.1

JTAG Programming ........................................................................................................... 8

2.2

Quad-SPI Programming .................................................................................................... 8

2.3

USB Host and MicroSD Programming .............................................................................. 9

Memory ......................................................................................................................... 9
3.1

DDR3 ................................................................................................................................. 9

3.2

Quad-SPI Flash................................................................................................................ 10

4Ethernet PHY ............................................................................................................... 11

5

Oscillators/Clocks ........................................................................................................ 126

USB UART Bridge (Serial Port) ...................................................................................... 13

7

PC – FPGA Data Transfer (DPTI / DSPI) .......................................................................... 13
7.1

Parallel Transfer Interface (DPTI) ................................................................................... 14

7.2

Serial Peripheral Interface (DSPI) ................................................................................... 15

DOC#: 502-316

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Nexys Video™ FPGA Board Reference Manual

89

USB HID Host ............................................................................................................... 15
8.1

HID Controller................................................................................................................. 15

8.2

Keyboard ........................................................................................................................ 16

8.3

Mouse............................................................................................................................. 17

Basic I/O ...................................................................................................................... 18

10 Pmod Connectors ......................................................................................................... 19
10.1

Dual Analog/Digital Pmod .......................................................................................... 20

11 Low Pin Count FMC Connector ..................................................................................... 21
12 MicroSD Slot ................................................................................................................ 21
13 HDMI ........................................................................................................................... 22
13.1

TMDS signals ............................................................................................................... 23

13.2

Auxiliary signals .......................................................................................................... 23

14 DisplayPort Output ...................................................................................................... 23
15 OLED ............................................................................................................................ 25
16 Audio Codec................................................................................................................. 26
17 Out-of-box Demo ......................................................................................................... 28

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Nexys Video™ FPGA Board Reference Manual

Overview
The Nexys Video board is a complete, ready-to-use
digital circuit development platform based on thelatest Artix-7™ Field Programmable Gate Array(FPGA) from Xilinx®. With its large, high-capacity
FPGA (Xilinx part number XC7A200T-1SBG484C),
generous external memories, high-speed digital video
ports, and 24-bit audio codec, the Nexys Video isperfectly suited for audio and video processing
applications. Several built-in peripherals, including
Ethernet, USB-UART, and a high bandwidth USB datatransfer protocol expand the connectivity of the
Nexys Video so that it can be cleanly integrated as asingle component of a large system. The Nexys Video
also includes provisions for direct human interaction
with a connector for USB-HID devices, an OLED
display, and a vast assortment of switches, buttons, and LEDs. Lastly, the FMC and Pmod connectors can be used
to add virtually any functionality or connection interface your application demands.
The Artix-7 FPGA is optimized for high performance logic, and offers more capacity, higher performance, and moreresources than earlier designs. Artix-7 200T features include:
•
•
•
•
•
•
•

33,650 logic slices, each with four 6-input LUTs and 8 flip-flops
Close to 13 Mbits of fast block RAM (3x more than the Nexys 4 DDR)
Ten clock management tiles, each with phase-locked loop (PLL)
740 DSP slices
Internal clock speeds exceeding 450 MHz
On-chip analog-to-digital converter (XADC)
Up to 3.75Gbps GTP transceivers

The Nexys Video also offers an improved collection of ports and peripherals, including:
•
•
•
•
•
•

8 user switches
USB-UART Bridge
HDMI Sink and HDMI Source
6 user push buttons
512MiB 800Mt/s DDR3
Pmod for XADC signals

•
•
•
•
•
•

8 user LEDs
160-pin FMC LPC connector
DisplayPort Source
User EEPROM
Serial Flash
Digilent Adept USB port for
programming and data

•
•
•
•
•
•

128x32 monochrome OLED display
MicroSD card connector
Audio codec w/ four 3.5mm jacks
10/100/1000 Ethernet PHY
Four Pmod ports
USB HID Host for mice, keyboards,
and USB MSD HostIn addition to being compatible with Xilinx's ISE® toolset, the Nexys Video also works with the new high®
performance Vivado Design Suite. It is supported under the free WebPACK™ license, so designs can be
implemented at no additional cost. This free license now includes the ability to create MicroBlaze™ soft-coreprocessor designs (in Vivado only), which greatly reduces the time needed to implement complex systems. Design
resources, example projects, device datasheets, and tutorials are available for download at the Nexys Video
Resource Center, reference.digilentinc.com/nexysvideo.

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Page 3 of 28

Nexys Video™ FPGA Board Reference Manual

Callout

Component Description

Callout

Component Description

1

Power jack14

MicroSD card slot (underneath)2Power Switch

15

Five pushbuttons

3Power indicator LED

16

Miscellaneous XADC pins

4

Pmod Header(s)17Programming mode jumper

5External fan control solder points

18

FMC header

6

FPGA programming done LED

19

FPGA configuration reset button

7

USB host connector

20

CPU reset button (for soft cores)

8

External configuration jumper (SD / USB)

21

Analog signal Pmod header (JXADC)

9Micro USB (UART) connector

22

Microphone/Audio connectors

10

Micro USB (JTAG) connector for USB
programming

23

DisplayPort output connector

11

LEDs (8)24

Ethernet connector

12

Slide Switches (8)25

HDMI output connector

13

OLED display

26

HDMI input connector

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Nexys Video™ FPGA Board Reference Manual

Regulatory Warning
Warning: This is a class A product. In a domestic environment this product may cause radio interference, in whichcase the user may be required to take adequate measures.

1

Power Supplies

The Nexys Video board can receive power from an external power supply through the center-positive barrel jack(J21) or the two-pin battery header (J22). The external supply voltage must be 12 V ±5 %. The Nexys Video cannot
be powered from the USB bus.
All Nexys Video power supplies can be turned on and off by a single logic-level power switch (SW8). Enables ofpower supplies not connected directly to the power switch are disabled indirectly. A power-good LED (LD16),
driven by the "power good" output of the on-board regulators, indicates that the supplies are turned on andoperating normally. An overview of the Nexys Video power circuit is shown in Fig. 1.

Figure 1. Nexys Video power circuit.

An external power supply can be used by plugging it into the power jack (J21). The supply must use a coax, centerpositive 2.1mm internal-diameter plug, and deliver 12VDC ±5 %. The minimum current rating of the supply
depends on the actual design implemented in the FPGA, but at least 3A of current (i.e., at least 36W of power) is
recommended.
Instead of a wall supply, an external battery pack can be used by connecting the battery's positive terminal to thepositive pin of J22 and the negative terminal to the negative pin. Incorrect polarity might cause permanent damage
to the board. To power the Nexys Video and any peripheral other than an FMC mezzanine card using the 12P0V
supply, the battery voltage must be in the 6-15 V range. Since the external power supply pin is wired directly to the
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Nexys Video™ FPGA Board Reference Manual
12P0V pin of the FMC connector, the battery voltage must be 12VDC ±5 % in FMC applications, the same as thewall supply specification. In any case, 15V is an absolute maximum.
Voltage regulator circuits from Analog Devices® create the different voltages required by the FPGA and on-board
peripherals from the main power input. Some regulators use the outputs of another regulator as input, depending
on design considerations. In some cases, this chaining helps in creating the proper power-on sequence for circuits.
In other cases, the chaining of power supply enables achieves the same purpose.
Table 1 provides information on maximum and typical currents for each power rail. The typical currents strongly
depend on FPGA configuration and the values provided represent medium size/speed designs.
SupplyCircuits

DeviceCurrent (max/typical)

3.3 V

FPGA I/O, USB, FMC, Clocks,
Pmod, Ethernet, SD slot,
Flash, DisplayPort

IC26: ADP5052

4A / 0.1 to 1.5A

1.0 V

FPGA Core

IC26: ADP5052

4A / 0.2 to 2A

1.8 V

FPGA Auxiliary

IC26: ADP5052

1.2A / 0.15A

1.5 V

DDR3 and FPGA I/O

IC26: ADP5052

1.2 A / 0.5 A

2.5 V

FPGA I/O and Ethernet

IC26: ADP5052

0.2 A / 0.1 A

VADJ(1.2-3.3 V)

User I/O, FMC, and FPGA I/O

IC28: ADP2384

2 A / 0.1 A

3.3 V

Audio analog supply

IC6: ADP150

0.15 A / 0.05 A

5.0 V

USB Host, HDMI

IC30: ADP2370

0.8 A / 0.5 A

MGT 1.0 V

Gigabit Transceivers VCC

IC31: ADP123

0.3 A

MGT 1.2 V

Gigabit Transceivers VTT

IC33: ADP123

0.3 A

XADC 1.8 V

XADC supply

IC34: ADP123

0.3 A

XADC 1.25 V

XADC reference

IC32: ADR127

5 mA

Table 1. Voltage rail power ratings.

The VADJ power rail requires special attention. It is a programmable voltage rail that powers the FMC mezzanine
connector, user push-buttons, switches, XADC Pmod connector, and the FPGA banks connected to these
peripherals (banks 15, 16). The feedback pin of the VADJ regulator is connected to an analog multiplexer controlled
by two FPGA signals, "SET_VADJ(1:0)". The multiplexer is able to change the resistor values in the feedback loop,
thereby changing the voltage on the regulator's output. Depending on the value set on the "SET_VADJ(1:0)" pins,
the possible voltages are listed in Table 2. The third control pin is the "VADJ_EN" signal, which can disable theregulator altogether. If these control pins are not used in the FPGA design, on-board pull resistors enable theregulator and set the VADJ voltage to 1.2 V.
An FPGA design can dynamically change the VADJ voltage to suit a certain FMC mezzanine card or application. Caremust be taken to disable the regulator first by bringing "VADJ_EN" low, setting "SET_VADJ(1:0)" and enabling theregulator again. Please note that for proper voltage levels in digital signals connected to VADJ-powered FPGA banks(ex. user push-buttons), the correct I/O standard still needs to be set in the design user constraints (XDC or UCF
file). See the schematic and/or the constraints file to determine which signals are in VADJ-powered banks. The
provided master UCF and XDC files assume the default VADJ voltage of 1.2V, declaring LVCMOS12 as the I/Ostandard for these signals.

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Nexys Video™ FPGA Board Reference Manual
SET_VADJ(1:0)
00 (default)
01
10
11

VADJ
1.2 V
1.8 V
2.5 V
3.3 V

Table 2. VADJ programmable voltages.

2

FPGA Configuration

After power-on, the Artix-7 FPGA must be configured (or programmed) before it can perform any functions. You
can configure the FPGA in one of four ways:
1.
2.
3.
4.

A PC can use the Digilent USB-JTAG circuitry (port J12, labeled "PROG") to program the FPGA any time thepower is on.
A file stored in the non-volatile serial (SPI) flash device can be transferred to the FPGA.
A programming file can be transferred to the FPGA from a microSD card.
A programming file can be transferred from a USB mass-storage device (ex. pen drive) attached to the
USB HID port.

Figure 2 shows the different options available for configuring the FPGA. An on-board "mode" jumper (JP4) and amedia selection jumper (JP3) select between the programming modes.

Micro-B USB
Connector (J13)6-pin JTAGHeader (J17)USB
Controller
JTAG
Port

1x6 JTAG
Header

SPI quad-mode
FlashMode (JP4)

Artix-7
M0
M2
M1

Micro SD
Connector (J3)Type A USB Host
Connector (J15)

SPI
Port

User I/O
Done

2
PIC24

SerialProg. Port

Prog

JP3

JP4

any

SPI Flash

any

JTAG
USB
MicroSD

Programming ModeMedia Select (JP3)

Figure 2. Nexys Video configuration options.

The FPGA configuration data is stored in files called bitstreams that have the .bit file extension. The ISE or Vivado
software from Xilinx can create bitstreams from VHDL or Verilog. In Vivado, the IP Integrator tool can also be used,which provides a graphical, block diagram-based design environment.
Bitstreams are stored in volatile memory cells within the FPGA. This data defines the FPGA's logic functions andcircuit connections, and it remains valid until it is erased by removing board power, by pressing the reset button
attached to the PROG input, or by writing a new configuration file using the JTAG port.
An Artix-7 200T bitstream is typically 77,845,216 bits and can take a long time to transfer depending on the
programming mode. The time it takes to program the Nexys Video can be decreased by compressing the bitstream
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Nexys Video™ FPGA Board Reference Manual
before programming, and then allowing the FPGA to decompress the bitstream itself during configuration.
Depending on design complexity, compression ratios of 10x can be achieved. Bitstream compression can be
enabled within the Xilinx tools (ISE or Vivado) to occur during generation. For instructions on how to do this,consult the Xilinx documentation for the toolset being used. This option is available for all programming modes.
Mode-specific speed-ups are also available. JTAG clock frequency can be set to the maximum supported by the
programming cable in iMPACT/Vivado Hardware Manager. Similarly, the clock frequency for the SPI Flash can beincreased in device properties (Vivado) or bitstream generation options (ISE). The microSD and USB mass-storage
device configuration modes already operate at their maximum possible speed.
After being successfully programmed, the FPGA will illuminate the "DONE" LED. Pressing the "PROG" button at any
time will reset the configuration memory in the FPGA. After being reset, the FPGA will immediately attempt toreprogram itself from whatever method has been selected by the programming mode jumpers.
The following sections provide greater detail about programming the Nexys Video using the different methods
available.

2.1

JTAG Programming

The Xilinx tools typically communicate with FPGAs using the Test Access Port and Boundary-Scan Architecture,commonly referred to as JTAG. During JTAG programming, a .bit file is transferred from the PC to the FPGA using
the onboard Digilent USB-JTAG circuitry (port J12) or an external JTAG programmer, such as the Digilent JTAG HS2,
attached to port J17. You can perform JTAG programming at any time after the Nexys Video has been powered on,
regardless of what the mode jumper (JP4) is set to. If the FPGA is already configured, then the existing
configuration is overwritten with the bitstream being transmitted over JTAG. Setting the mode jumper to the JTAG
setting is useful to prevent the FPGA from being configured from any other bitstream source until a JTAG
programming occurs.
Programming the Nexys Video with an uncompressed bitstream using the on-board USB-JTAG circuitry usuallytakes around four seconds with a 30 MHz JTAG clock.
JTAG programming can be done using the hardware server in Vivado or the iMPACT tool included with ISE. The
Nexys Video Programming Guide available on the Nexys Video Resource Center walks through the process ofbuilding a bitstream and using it to program the Nexys Video.

2.2

Quad-SPI Programming

For the FPGA to be able to configure itself from the SPI Flash, it first needs to be programmed with the bitstream.
This is called indirect programming and is a two-step process controlled by Hardware Manager (Vivado) or iMPACT(ISE). First, the FPGA is programmed with a design that can program flash devices, and then data is transferred to
the flash device via the FPGA circuit (this complexity is hidden from the user by the Xilinx tools). After the flash
device has been programmed, it can automatically configure the FPGA at a subsequent power-on or reset event as
determined by the mode jumper setting. Programming files stored in the flash device will remain until they are
overwritten, regardless of power-cycle events.
Programming the flash can take as long as four to five minutes, which is mostly due to the lengthy erase processinherent to the memory technology. Once written however, FPGA configuration can be very fast; taking less than asecond. Bitstream compression, SPI bus width, and configuration rate are factors controlled by the Xilinx tools that
can affect configuration speed. The on-board flash has a Quad-SPI interface, which supports single (x1), dual (x2),and quad (x4) modes. The quad mode results in the fastest possible data transfer rate. In order for the quad mode

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Nexys Video™ FPGA Board Reference Manual
to work, the bitstream needs to be generated with the x4 bus width option (Vivado device property) and the nonvolatile quad configuration bit in the flash needs to be enabled. The Nexys Video is shipped with this bit enabled.
Indirect programming of the flash can also be done using the iMPACT tool included with ISE. The correct part to be
set in the tools is s25fl256xxxxxx0 from the manufacturer Spansion®.
The Nexys Video Programming Guide, which is available on the Nexys Video Resource Center, walks through theprocess of programming the Quad-SPI flash from Vivado.

2.3

USB Host and MicroSD Programming

You can program the FPGA from a pen drive attached to the USB-HID port (J15) or a microSD card inserted into J3
by doing the following:
1.
2.
3.
4.
5.
6.

Format the storage device (pen drive or microSD card) with a FAT32 file system.
Place a single .bit configuration file in the root directory of the storage device.
Attach the storage device to the Nexys Video.
Set the JP4 Programming Mode jumper on the Nexys Video to "USB/SD".
Select the desired storage device using JP3.
Push the PROG button or power-cycle the Nexys Video.

The FPGA will automatically configure with the .bit file on the selected storage device. Any .bit files that are notbuilt for the proper Artix-7 device will be rejected by the FPGA.
The Auxiliary Function Status, or "BUSY" LED (LD14), gives visual feedback on the state of the configuration process
when the FPGA is not yet programmed:•••

When steadily lit, the auxiliary microcontroller is either booting up or currently reading the configuration
medium (microSD or pen drive) and downloading a bitstream to the FPGA.
A slow pulse means the microcontroller is waiting for a configuration medium to be plugged in.
In case of an error during configuration, the LED will blink rapidly. This could mean that the device
plugged in is not recognized, it is not properly formatted, or the bitstream is not compatible with the
FPGA.

When the FPGA has been successfully configured, the behavior of the LED is application-specific. For example, if a
USB keyboard is plugged in, a rapid short blink will signal the receipt of an HID input report from the keyboard.

3

MemoryThe Nexys Video board contains two external memories: a 512MiByte volatile DDR3 memory and a 32MiByte nonvolatile Serial Flash device. The DDR3 uses a 16-bit wide memory component soldered on the board with industrystandard interface. The Serial Flash is on a dedicated quad-mode (x4) SPI bus.

3.1

DDR3

The Nexys Video includes one Micron MT41K256M16HA-187E DDR3 memory component creating a single rank,
16-bit wide interface. It is routed to a 1.5V-powered high range (HR) FPGA bank with 50 ohm controlled singleended trace impedance. 50 ohm internal terminations in the FPGA are used to match the trace characteristics.
Similarly, on the memory side, on-die terminations (ODT) are used for impedance matching.
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Nexys Video™ FPGA Board Reference ManualFor proper operation of the memory, a memory controller and physical layer (PHY) interface needs to be includedin the FPGA design. The Xilinx 7 series memory interface solutions core generated by the memory interface
generator (MIG) Wizard hides away the complexities of a DDR3 interface. Depending on the tool used (ISE, EDK, or
Vivado), the MIG Wizard can generate a native FIFO-style or an AXI4 interface to connect to user logic. This
workflow allows the customization of several DDR3 parameters optimized for the particular application. Table 3
below lists the MIG Wizard settings optimized for the Nexys Video.
SettingMemory typeMax. clock period
Clock ratio
Memory type
Memory part
Memory voltage
Data width
Data mask
Input clock period
Output driver impedance
Chip Select pin
Rtt (nominal) – On-die termination
Internal Vref
Internal termination impedance

Value
DDR3 SDRAM
2500ps (800Mbps data rate)
4:1
Components
MT41K256M16HA-125
1.5V
16
Enabled10000ps (100 MHz)RZQ/6
Disabled
RZQ/6
Enabled50ohmsTable 3. DDR3 settings for the Nexys Video.

The MIG Wizard will require the fixed pin-out of the memory signals to be entered and validated before generating
the IP core. For your convenience an importable UCF file and MIG .prj file is provided on the Nexys Video Resource
center to speed up the process.
For more details on the Xilinx memory interface solutions, refer to the "7 Series FPGAs Memory Interface Solutions
User Guide" (ug586).

3.2

Quad-SPI FlashNon-volatile storage is provided by a Spansion S25FL256S flash memory. FPGA configuration files can be written to
flash memory, and mode settings are available to cause the FPGA to automatically read a configuration from thisdevice at power on. An Artix-7 200T configuration file requires just over 9 MiB (mebibyte) of memory, leaving
about 70% of the flash device available for user data. Or, if the FPGA is being configured from another source, thewhole memory can be used for custom data.
The contents of the memory can be manipulated by issuing certain commands on the SPI bus. The implementationof this protocol is outside the scope of this document. All signals in the SPI bus, except SCK, are general-purpose
user I/O pins after FPGA configuration. SCK is an exception because it remains a dedicated pin even after
configuration. Access to this pin is provided through a special FPGA primitive called STARTUPE2.
NOTE: Refer to the manufacturer's data sheets and Xilinx user guides for more information.

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Nexys Video™ FPGA Board Reference Manual

SPI Flash

Artix-7

CS#
SDI/DQ0
SDO/DQ1
WP#/DQ2
HLD#/DQ3SCK SPI Flash

T19
P22
R22
P21
R21
L12/CCLK

Figure 3. Nexys Video SPI Flash pin-out.

4

Ethernet PHY

The Nexys Video board includes a Realtek RTL8211E-VL PHY paired with an RJ-45 Ethernet jack with integrated
magnetics to implement a 10/100/1000 Ethernet port for network connection. The PHY interfaces with the FPGA
via RGMII for data and MDIO for management. Bank 13 powered at 2.5V is populated with these signals. The
auxiliary interrupt (INT_B) and power management (PME_B) signals are also wired to bank 13. The reset signal(RST_B) is the only one wired to a different bank (34), powered at 3.3V. The connection diagram can be seen in Fig.
4.
At power-on reset, the PHY is set to the following defaults using the configuration pins in parenthesis:•••

Auto-negotiation enabled, advertising all 10/100/1000 modes (AN[1:0])
PHY address=00001 (PHY_AD[2:0])
No delay for TXD and RXD relative to TXC and RXC for data latching (RXDLY, TXDLY)

If an Ethernet cable is plugged in, an establishing link is attempted straight after power-up, even if the FPGA is notprogrammed.
Three status indicator LEDs are on-board near the RJ-45 connector that indicate traffic (LD10) and valid link state(LD9). Table 4 below shows the default behavior.
Function

Designator

State

Description

ACT

LD10

Blinking

Transmitting or receiving

LINK

LD9

On

Link up

Blinking 0.4s ON, 2s OFF

Link up, Energy Efficient Ethernet (EEE) modeOn

Link up, no traffic

Off

Link down

Blinking

Link up, traffic

USER

LD8

Table 4. Ethernet status LEDs.

The on-board PHY implements Layer 1 in the Ethernet stack, interfacing between the physical copper medium andthe media access control (MAC). The MAC must be implemented in the FPGA and mapped to the PHY's RGMII
interface. Vivado-based designs can use the Xilinx AXI Ethernet Subsystem IP core to implement the MAC and wire
it to the processor and the memory subsystem. At the time of writing, the IP core needed to be licensed separately

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Page 11 of 28

Nexys Video™ FPGA Board Reference Manualwith Xilinx part number EF-DI-TEMAC-PROJ or EF-DI-TEMAC-SITE. A free evaluation of this core is available;
however, the design will stop working after running for approximately 8 hours.
On an Ethernet network, each node needs a unique MAC address. To this end, a Microchip 24AA025E48 EEPROM
2
is provided on the Nexys Video. On one hand, it is a read-writeable EEPROM that can be accessed via I C. On theother hand, it features a read-only memory section that comes pre-programmed with a unique identifier. This
unique identifier can be read and used as a MAC address, avoiding a possible address conflict on the network. The
device address of the EEPROM is 1010000b. The out-of-box Ethernet demo uses the unique MAC to allow
connecting several Nexys Video boards to the same network.
A tutorial that describes how to create a simple server using a MicroBlaze softcore processor and the Xilinx AXI
Ethernet Subsystem IP core is available on the Nexys Video Resource Center.
Use only shielded Ethernet cables.
Y16
AA16

MDIO
MDC

AB16
AA15
AB15
AB11
W10
V13

RXD0/SELRGV
RXD1/TXDLY
RXD2/AN0
RXD3/AN1RXCTL/PHY_AD2
RXC

Y12
W12
W11
Y11
V10
AA14

TXD0
TXD1
TXD2
TXD3
TXCTL
TXC

Y14
U7

INTB
PHYRSTB

W5
V5

RJ-45 withmagnetics
8

ACT LED (LD10)

LED0/PHY_AD0

EEPROM

LED1/PHY_AD1

LINK LED(LD9)

LED2/RXDLY

Artix-7

25 MHzOscillator
DSC1101CE2CKXTAL1

LINK LED (LD8)Realtek RTL8211E

Figure 4. Pin connections between the Artix-7 and the Ethernet PHY.

5

Oscillators/Clocks

The Nexys Video board includes a single 100 MHz crystal oscillator connected to pin R4 (R4 is a MRCC input onbank 34). The input clock can drive MMCMs or PLLs to generate clocks of various frequencies and with known
phase relationships that may be needed throughout a design. Some rules restrict which MMCMs and PLLs may be
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Nexys Video™ FPGA Board Reference Manual
driven by the 100 MHz input clock. For a full description of these rules and of the capabilities of the Artix-7 clocking
resources, refer to the "7-Series FPGAs Clocking Resources User Guide" (ug472) available from Xilinx.
Xilinx offers the Clocking Wizard IP core to help users generate the different clocks required for a specific design.
This wizard will properly instantiate the needed MMCMs and PLLs based on the desired frequencies and phaserelationships specified by the user. The wizard will then output an easy-to-use wrapper component around theseclocking resources that can be inserted into the user's design. The clocking wizard can be accessed from within the
Vivado Block Design or Core Generator tools.

6

USB UART Bridge (Serial Port)

The Nexys Video includes an FTDI FT232R USB-UART bridge (attached to connector J13) that lets you use PC
applications to communicate with the board using standard Windows COM port commands. Free USB-COM port
drivers, available from Windows Update or www.ftdichip.com under the "Virtual Com Port" or VCP heading,convert USB packets to UART/serial port data. Serial port data is exchanged with the FPGA using a two-wire serial
port (TXD/RXD) with no handshake signals. After the drivers are installed, I/O commands can be used from the PC
directed to the COM port to produce serial data traffic on the V18 and AA19 FPGA pins.
Two on-board status LEDs provide visual feedback on traffic flowing through the port: the transmit LED (LD13) andthe receive LED (LD12). Signal names that imply direction are from the point-of-view of the DTE (Data Terminal
Equipment), in this case the PC.
The connections between the FT232R and the Artix-7 are shown in Fig. 5.

2
Micro-USB
(J13)

TXD

V18

RXD

AA19

FT232R

Artix-7

Figure 5. Nexys Video FT232R connections.

7

PC – FPGA Data Transfer (DPTI / DSPI)The Nexys Video provides two interface types that can be used to transfer user data between a PC and an FPGA
design. Both of the interfaces have a software component, a Digilent Adept API, and a physical interface between
the FPGA and the USB controller. Calling API functions on the PC will either present or request data on the FPGA
pins according to the chosen protocol. The functionality is implemented using the on-board dual-port FT2232 USB
controller. One port is used exclusively for JTAG, while the other either DPTI or DSPI. Since the interfaces sharepins, DPTI and DSPI cannot be used simultaneously.

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JTAG

Micro-USB(J12)

D0/SCK
D1/MOSI
D2/MISO
D3/SS
D4
D5
D6
D7
RXF#
TXE#
RD#
WR#
SIWU#
OE#
CLKOUT

JTAG
U20
P14
P15
U17
R17
P16
R18
N14
N17
Y19
P19
R19
P17
V17
Y18

FT2232H

Artix-7

Figure 6. USB-FPGA interfaces provided by the USB PROG port.

7.1

Parallel Transfer Interface (DPTI)

DPTI is an 8-bit wide parallel FIFO-style data interface that offers higher bandwidth than DSPI. In FTDI-terminology,
DPTI is equivalent to "FT245-style Asynchronous or Synchronous FIFO Interface". It is available in both synchronousand asynchronous modes, configurable from the DPTI API. In synchronous mode, data transfer is timed by theclock provided by the USB controller that is input to the FPGA. In asynchronous mode, data transfer is happening
on transitions of read and write control signals. The USB controller emulates a FIFO memory, providing status
signals about the availability of data to be read or free space for data to be written. The FPGA controls datatransfer by read, write, and output enable signals.

D[7:0]
RXF#
TXE#
RD#
WR#

Direction (FPGA
Point of View)
I/O
Input
Input
OutputOutput

SIWU#

Input

OE#

Output

CLKO

Input

SignalDescription
Data bus.
When low, data is available for reading from the FIFO.
When low, data can be written to the FIFO.
A low-pulse triggers data to be read out from the FIFO.
A low-pulse triggers data to be written to the FIFO.
Send immediate or Wake-up function. In normal mode a low pulse triggers
sending a data packet with the data currently in the FIFO, even if below thenormal packet size. In suspend mode a low pulse can wake up the Host PC.
When low, the data bus is driven by the USB controller (read transfer). Whenhigh, the bus is driven by the FPGA (write transfer).
60 MHz clock used in synchronous mode. Data is launched and can be
captured on the rising edge.
Table 5. DPTI signal description.

For more information, see the FT2232H data sheet.

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7.2

Serial Peripheral Interface (DSPI)An industry-standard SPI interface can also be used for transferring data. It uses only four signals for serial fullduplex communication. The USB controller acts as a SPI master, with the FPGA taking the slave role. The USB
controller initiates a transaction after API function calls are made and transfers data in both directions
simultaneously.
Signal
SCK
MOSI
MISO
SS

Direction (FPGA)
Input
Output
Input
Input

Description
Data bus.
When low, data is available for reading from the FIFO.
When low, data can be written to the FIFO.
A low-pulse triggers data to be read out from the FIFO.
Table 6. DSPI signal description.

For more information, see the FT2232H data sheet.

8

USB HID Host

The Auxiliary Function microcontroller (Microchip® PIC24FJ128) provides the Nexys Video with USB HID hostcapability. After power-up, the microcontroller is in configuration mode, either downloading a bitstream to the
FPGA or waiting on it to be programmed from other sources. Once the FPGA is programmed, the microcontroller
switches to application mode, which is USB HID Host in this case. Firmware in the microcontroller can drive amouse or a keyboard attached to the type A USB connector at J15 labeled "USB Host." Hub support is not currently
available, so only a single mouse or a single keyboard can be used. The PIC24 drives several signals into the FPGA:
two are used to implement a standard PS/2 interface for communication with a mouse or keyboard, and theothers are connected to the FPGA's two-wire serial programming port, so the FPGA can be programmed from a filestored on a USB pen drive or microSD card.

SD MICRO (J3)

microSD

SD/USB (JP3)FPGA
Config2

HOST (J15)

User I/O
2

PS2_CLK
PS2_DATFPGA
Config
W17
N13

PIC24FJ128

Artix-7

Figure 7. Nexys Video PIC24 connections.

8.1

HID Controller

The Auxiliary Function microcontroller hides the USB HID protocol from the FPGA and emulates an old-style PS/2
bus. The microcontroller behaves just like a PS/2 keyboard or mouse would. This means new designs can reuse
existing PS/2 IP cores. Mice and keyboards that use the PS/2 protocol use a two-wire serial bus (clock and data) tocommunicate with a host. On the Nexys Video, the microcontroller emulates a PS/2 device, while the FPGA plays
the role of the host. Both the mouse and the keyboard use 11-bit words that include a start bit, data byte (LSB
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Nexys Video™ FPGA Board Reference Manual
first), odd parity, and stop bit, but the data packets are organized differently, and the keyboard interface allows bidirectional data transfers (so the host device can illuminate state LEDs on the keyboard). Bus timings are shown in
Fig. 8.

Edge 0

Tck Tck‘0’ start bit

Thld

Edge 10CLOCK‘1’ stop bit

DATA
Tsu
SymbolParameterMin
30us
TCK Clock timeData-to-clock setup time 5us
TSU
THLD Clock-to-data hold time 5us

Max
50us
25us
25us

Figure 8. PS/2 device-to-host timing diagram.

The clock and data signals are only driven when data transfers occur; otherwise, they are held in the idle state at
logic '1'. This requires that when the PS/2 signals are used in a design, internal pull-ups must be enabled in the
FPGA on the data and clock pins. The clock signal is normally driven by the device, but may be held low by the hostin special cases. The timings define signal requirements for mouse-to-host communications and bi-directional
keyboard communications. A PS/2 interface circuit can be implemented in the FPGA to create a keyboard ormouse interface.
When a keyboard or mouse is connected to the Nexys Video, a "self-test passed" command (0xAA) is sent to thehost. After this, commands may be issued to the device. Since both the keyboard and the mouse use the same
PS/2 port, one can tell the type of device connected using the device ID. This ID can be read by issuing a Read ID
command (0xF2). Also, a mouse sends its ID (0x00) right after the "self-test passed" command, which distinguishes
it from a keyboard.

8.2

Keyboard

PS/2 uses open-collector drivers so the keyboard, or an attached host device, can drive the two-wire bus (if thehost device will not send data to the keyboard, then the host can use input-only ports).
PS/2-style keyboards use scan codes to communicate key press data. Each key is assigned a code that is sent
whenever the key is pressed. If the key is held down, the scan code will be sent repeatedly about once every
100ms. When a key is released, an F0 key-up code is sent, followed by the scan code of the released key. If a key
can be shifted to produce a new character (like a capital letter), then a shift character is sent in addition to the scancode, and the host must determine which ASCII character to use. Some keys, called extended keys, send an E0
ahead of the scan code (and they may send more than one scan code). When an extended key is released, an E0 F0
key-up code is sent, followed by the scan code. Scan codes for most keys are shown in Fig. 9.

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Nexys Video™ FPGA Board Reference Manual

Figure 9. Keyboard scan codes.

A host device can also send data to the keyboard. Table 7 shows a list of some common commands a host might
send.
Command

ActionED

Set Num Lock, Caps Lock, and Scroll Lock LEDs. Keyboard returns FA after receiving ED, thenhost sends a byte to set LED status: bit 0 sets Scroll Lock, bit 1 sets Num Lock, and bit 2 sets
Caps lock. Bits 3 to 7 are ignored.

EE

Echo (test). Keyboard returns EE after receiving EE

F3

Set scan code repeat rate. Keyboard returns F3 on receiving FA, then host sends second byte
to set the repeat rate.

FE

Resend. FE directs keyboard to re-send most recent scan code.

FF

Reset. Resets the keyboard.
Table 7. Keyboard commands.

The keyboard can send data to the host only when both the data and clock lines are high (or idle). Because thehost is the bus master, the keyboard must check to see whether the host is sending data before driving the bus. To
facilitate this, the clock line is used as a "clear to send" signal. If the host drives the clock line low, the keyboard
must not send any data until the clock is released. The keyboard sends data to the host in 11-bit words that
contain a '0' start bit, followed by 8-bits of scan code (LSB first), followed by an odd parity bit, and terminated witha '1' stop bit. The keyboard generates 11 clock transitions (at 20 to 30 KHz) when the data is sent, and data is valid
on the falling edge of the clock.

8.3

Mouse

Once entered in stream mode and data reporting enabled, the mouse outputs a clock and data signal when it is
moved; otherwise, these signals remain at logic '1.' Each time the mouse is moved, three 11-bit words are sentfrom the mouse to the host device, as shown in Fig. 10. Each of the 11-bit words contains a '0' start bit, followed by
8 bits of data (LSB first), followed by an odd parity bit, and terminated with a '1' stop bit. Thus, each datatransmission contains 33 bits, where bits 0, 11, and 22 are '0' start bits, and bits 11, 21, and 33 are '1' stop bits. The
three 8-bit data fields contain movement data as shown in the figure above. Data is valid at the falling edge of theclock, and the clock period is 20 to 30 KHz.

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The mouse assumes a relative coordinate system wherein moving the mouse to the right generates a positive
number in the X field, and moving to the left generates a negative number. Likewise, moving the mouse up
generates a positive number in the Y field, and moving down represents a negative number (the XS and YS bits inthe status byte are the sign bits – a '1' indicates a negative number). The magnitude of the X and Y numbers
represent the rate of mouse movement: the larger the number, the faster the mouse is moving (the XV and YV bitsin the status byte are movement overflow indicators – a '1' means overflow has occurred). If the mouse moves
continuously, the 33-bit transmissions are repeated every 50ms or so. The L and R fields in the status byte indicate
Left and Right button presses (a '1' indicates the button is being pressed).
Mouse status byte
1

0

L

R

0

1 XS YS XY YY P

Start bit

Stop bit

X direction byte
1

Y direction byte

0 X0 X1 X2 X3 X4 X5 X6 X7 P

Start bit

Stop bit

1

0

Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 P

Start bit

Idle state

1

Stop bit
Idle state

Figure 10. Mouse data format.

The microcontroller also supports Microsoft® IntelliMouse®-type extensions for reporting back a third axis
representing the mouse wheel, as shown in Table 8.
Command
EA
F4
F5
F3

ActionSet stream mode. The mouse responds with "acknowledge" (0xFA) then resets its movement
counters and enters stream mode.
Enable data reporting. The mouse responds with "acknowledge" (0xFA) then enables datareporting and resets its movement counters. This command only affects behavior in stream
mode. Once issued, mouse movement will automatically generate a data packet.
Disable data reporting. The mouse responds with "acknowledge" (0xFA) then disables datareporting and resets its movement counters.
Set mouse sample rate. The mouse responds with "acknowledge" (0xFA) then reads one morebyte from the host. This byte is then saved as the new sample rate, and a new "acknowledge"
packet is issued.

FE

Resend. FE directs mouse to re-send last packet.

FF

Reset. The mouse responds with "acknowledge" (0xFA) then enters reset mode.
Table 8. Microsoft IntelliMouse-type extensions, commands, and actions.

9

Basic I/O

The Nexys Video board includes eight slide switches, five push buttons, and eight individual LEDs. The pushbuttons
and slide switches are connected to the FPGA via series resistors to prevent damage from inadvertent short circuits(a short circuit could occur if an FPGA pin assigned to a pushbutton or slide switch was inadvertently defined as an
output). The five pushbuttons arranged in a plus-sign configuration are "momentary" switches that normallygenerate a low output when they are at rest, and a high output only when they are pressed. The red pushbuttonlabeled "CPU RESET," on the other hand, generates a high output when at rest and a low output when pressed.
The CPU RESET button is intended to be used in processor designs to reset the processor, but you can also use it asa general purpose pushbutton. Slide switches generate constant high or low inputs depending on their position.

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Nexys Video™ FPGA Board Reference Manual
VADJ

Buttons

M17

BTNR

M18

BTNU

P18

BTND

N17

BTNC

LD0

H17
K15
J13
N14
R18
V17
U17
U16

P17

BTNL

LD1
LD2
LD3
LD4
LD5
LD6
LD7

LEDs

VADJ

Slide
Switches

SW0

J15

SW1

L16

SW2

M13

SW3

R15

SW4

R17

SW5

T18

SW6

U18

SW7

R13

1.5V

C12

BTN6
CPU Reset

Artix-7

Figure 11. General purpose I/O connections.

The eight individual high-efficiency LEDs are anode-connected to the FPGA via 100-ohm resistors, so they will turnon when a logic high voltage is applied to their respective I/O pin. Additional LEDs that are not user-accessible
indicate power-on, FPGA programming status, and USB and Ethernet port status.

10

Pmod Connectors

The Pmod connectors are arranged in a 2x6 right-angle, 100-mil female connectors that mate with standard 2x6
pin headers. Each 12-pin Pmod connector provides two power pins (6 and 12), two ground pins (5 and 11), andeight logic signals. The VCC and Ground pins can deliver up to 1A of current. Pin assignments for the Pmod I/Oconnected to the FPGA are shown in Fig. 12.

VCC GND

8 signals

Pin 6

Pin 1

Pin 12

Figure 12. Pmod connectors- front view as loaded on PCB.

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Nexys Video™ FPGA Board Reference Manual
The Nexys Video features four Pmod connectors of different "styles" with subtle differences between them. Table
9 summarizes these differences.
Pmod
connector

Power

Analog/Digital

JXADC

VADJ

Dual

JA

3.3 V

Digital-only

JB, JC

3.3 V

Digital-only

Seriesprotection

RoutingDifferential; Pairs:
1-7,2-8,3-8,4-10
Single-ended
Differential; Pairs:
1-2,3-4,7-8,9-10

100 ohm
200 ohm
0 ohm

Recommended usage
Analog inputs; LVDS_25
input/output (VADJ=2.5V)<10 MHz, LVCMOS33>=10MHz; LVDS_25 input only,or TMDS_33 input/output

Table 9. Pmod differences.

JXADC is a dual digital/analog Pmod wired to auxiliary analog FPGA input pins (see description below). JA, JB, andJC are digital-only but routed in a different manner. JA signal traces are routed as single-ended signals with nolength matching or characteristic impedance guarantees. JB and JC connector signals, on the other hand, arerouted differentially in pairs at 100 ohm characteristic impedance. Inter-pair matching is +- 20mm. The series
resistor on these two Pmods are replaced by 0 ohm shunts, so care must be exercised not to use voltages higher
than 3.3V, or short FPGA-driven pins.
For slow, single-ended digital signals below 10 MHz, all Pmod connectors are equivalent, assuming VADJ is set to 3.3
V (see the Power Supplies section). For higher frequencies, the routing and series protection need to be taken into
account as well.
PMOD Pinouts
JA1: AB22

JB1: V9

JC1: Y6JXADC1: J14

JA2: AB21

JB2: V8

JC2: AA6JXADC2: H13

JA3: AB20

JB3: V7

JC3: AA8JXADC3: G15

JA4: AB18

JB4: W7

JC4: AB8JXADC4: J15

JA7: Y21

JB7: W9

JC7: R6JXADC7: H14

JA8: AA21

JB8: Y9

JC8: T6JXADC8: G13

JA9: AA20

JB9: Y8

JC9: AB7JXADC9: G16

JA10: AA18

JB10: Y7

JC10: AB6JXADC10: H15

Table 10. Nexys Video Pmod pin assignments.

Digilent produces a large collection of Pmod accessory boards that can attach to the Pmod expansion connectors
to add ready-made functions like A/Ds, D/As, motor drivers, sensors, and other functions. Visit Digilent's website
and check out the Pmod category for more information.

10.1 Dual Analog/Digital Pmod
The on-board Pmod expansion connector labeled "JXADC" is wired to the auxiliary analog input pins of the FPGA.
Depending on the configuration, this connector can be used to input differential analog signals to the analog-todigital converter inside the Artix-7 (XADC). Any or all pairs in the connector can be configured either as analog
input or digital input-output.
The Dual Analog/Digital Pmod on the Nexys Video differs from the rest in the routing of its traces. The eight data
signals are grouped into four pairs, with the pairs routed closely coupled for better analog noise immunity.
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Nexys Video™ FPGA Board Reference Manual
Furthermore, each pair has a partially loaded anti-alias filter (100 ohm, 1 nF) laid out on the PCB. The filter does
not have capacitors C5, C8, C9, and C10. In designs where such filters are desired, the capacitors can be manuallyloaded by the user.
NOTE: The coupled routing and the anti-alias filters might limit the data speeds when used for digital signals.
The XADC core within the Artix-7 is a dual channel 12-bit analog-to-digital converter capable of operating at 1
MSPS. Either channel can be driven by any of the auxiliary analog input pairs connected to the JXADC header. The
XADC core is controlled and accessed from a user design via the Dynamic Reconfiguration Port (DRP). The DRP also
provides access to voltage monitors that are present on each of the FPGA's power rails, and a temperature sensor
that is internal to the FPGA. For more information on using the XADC core, refer to the Xilinx document titled "7Series FPGAs and Zynq-7000 All Programmable SoC XADC Dual 12-Bit 1 MSPS Analog-to-Digital Converter User
Guide" (ug480). A simple reference project that uses the XADC core can be found on the Nexys Video Resource
Center.

11

Low Pin Count FMC Connector

The Nexys Video includes an FPGA mezzanine card (FMC) standard-conforming carrier card connector that enables
connecting mezzanine modules compliant with the same standard. Nexys Video-based designs can now be easily
extended with custom or off-the-shelf high-performance modules.
The actual connector used is a Samtec ASP-134603-01, the low-pin count, 10mm stacking height variant of thestandard. It wires 34 differential pairs to regular FPGA user I/O pins powered by a voltage supply (VADJ) adjustablein the 1.2V-3.3V range. It also wires a 1 gigabit transceiver lane and its accompanying clock, the JTAG chain andauxiliary signals, and various voltage rails required by the standard. Thanks to the flexible voltage range supportedby the Nexys Video, it allows high compatibility with existing and future FMC modules. It essentially allows the fullrange of I/O standards supported by the Artix-7 I/O architecture over the FMC connector. The FPGA can even be
programmed to recognize the capabilities of a connected module and change the VADJ voltage on-the-fly.
The pinout of the FMC connector can be found in the UCF/XDC constraints file available on www.digilentinc.com.
The gigabit transceiver lane includes a receive pair, a transmit pair, and a reference clock input to the FPGA, allgoing to MGT bank 216. The transceiver lane is wired to lane 3 (GTPE2_CHANNEL_X0Y7). The reference clock is
wired to REFCLK1 of the same bank (GTPE2_COMMON_X0Y1). It is important to keep in mind that bank 216, being
the only one available in this FPGA package, is shared between the DisplayPort source and FMC ports. Dependingon the exact application, simultaneous usage of the FMC gigabit lane and DisplayPort might not be possible.
Regular FMC I/O signals are not affected.

12MicroSD Slot

The Nexys Video provides a microSD slot for both FPGA configuration and user access. The on-board Auxiliary
Function microcontroller shares the SD card bus with the FPGA. Before the FPGA is configured, the microcontroller
must have access to the SD card via SPI interface. Once a bit file is downloaded to the FPGA (from any source), themicrocontroller powers off the SD slot and relinquishes control of the bus. The FPGA design will find the SD card inan unpowered state.

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All of the SD pins on the FPGA are wired to support full SD speeds in native interface mode, as shown in Fig. 13.
The SPI interface is also available, if needed. Once control over the SD bus is passed from the microcontroller tothe FPGA, the SD_RESET signal needs to be actively driven low by the FPGA to power the microSD card slot. For
information on implementing an SD card controller, refer to the SD card specification available at www.sdcard.org.
3.3V
SD_RESET
E2
F1
E1
C1
B1
D2
C2
A1

VDD
DAT2
DAT1
CMD
CLK
DAT3
DAT0
CARD_DETECTSD MICRO (J3)

Artix-7

Figure 13. Artix-7 microSD card connector interface (PIC24 connections not shown).

13

HDMI

The Nexys Video board contains two buffered HDMI ports: one source port J8 (output), and one sink port J9(input). Both ports use HDMI type-A receptacles and include an HDMI buffer: An AD8195 buffer for input and a
TMDS141 for output. The buffers work by terminating, equalizing, conditioning, and forwarding the HDMI stream
between the connector and FPGA pins.
Both HDMI and DVI systems use the same TMDS signaling standard, directly supported by Artix-7 user I/O
infrastructure. Also, HDMI sources are backward compatible with DVI sinks, and vice versa. Thus, simple passive
adaptors (available at most electronics stores) can be used to drive a DVI monitor or accept a DVI input. The HDMI
receptacle only includes digital signals, so only DVI-D mode is possible.
The 19-pin HDMI connectors include three differential data channels, one differential clock channel, five GND
connections, a one-wire Consumer Electronics Control (CEC) bus, a two-wire Display Data Channel (DDC) bus that is2
essentially an I C bus, a Hot Plug Detect (HPD) signal, a 5V signal capable of delivering up to 50mA, and one
reserved (RES) pin. All are wired to the FPGA with the exception of RES.
Pin/Signal

J8 (source)

J9 (sink)

Description

FPGA pin

Description

FPGA pinD[2]_P, D[2]_N

Data output

AB3, AB2

Data input

U2, V2

D[1]_P, D[1]_N

Data output

AA1, AB1

Data input

W2, Y2

D[0]_P, D[0]_N

Data output

W1, Y1

Data input

Y3, AA3

CLK_P, CLK_N

Clock output

T1, U1Clock input

V4, W4CEC

Consumer Electronics Control
bidirectional

AA4

Consumer Electronics Control
bidirectional

AA5SCL, SDA

DDC bidirectional

U3, V3

DDC bidirectional

Y4, AB5

HPD/HPA

Hot-plug detect input

AB13

Hot-plug assert output

AB12

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5V0Powered from 5V rail

N/A

TXEN

Powers auxiliary signals

N/A

Transmitter enable output

R3

Table 11. HDMI pin description and assignment.

13.1 TMDS signals
HDMI/DVI is a high-speed digital video stream interface using transition-minimized differential signaling (TMDS).
To make proper use of either of the HDMI ports, a standard-compliant transmitter or receiver needs to be
implemented in the FPGA. The implementation details are outside the scope of this manual. Check out the Nexys
Video Resource Center for ready-to-use reference IP.

13.2 Auxiliary signals
A pull-down resistor on the TXEN signal makes sure the sink buffer's transmitter facing the FPGA is disabled bydefault. An FPGA design using the sink port needs to actively drive this pin high for the buffer to pass data through.
Whenever a sink is ready and wishes to announce its presence, it connects the 5V0 supply pin to the HPD pin. On
the Nexys Video, this is done by driving the Hot Plug Assert signal high. Note: this should only be done after a DDC
channel slave has been implemented in the FPGA and is ready to transmit display data.
The Display Data Channel, or DDC, is a collection of protocols that enable communication between the display
2(sink) and graphics adapter (source). The DDC2B variant is based on I C, the bus master being the source and thebus slave the sink. When a source detects high level on the HPD pin, it queries the sink over the DDC bus for video
capabilities. It determines whether the sink is DVI or HDMI-capable and what resolutions are supported. Only
afterwards will video transmission begin. Refer to VESA E-DDC specifications for more information.
The Consumer Electronics Control, or CEC, is an optional protocol that allows control messages to be passed
around on an HDMI chain between different products. A common use case is a TV passing control messages
originating from a universal remote to a DVR or satellite receiver. It is a one-wire protocol at 3.3V level connected
to an FPGA user I/O pin. The wire can be controlled in an open-drain fashion allowing for multiple devices sharing acommon CEC wire. Refer to the CEC addendum of HDMI 1.3 or later specifications for more information.

14

DisplayPort Output

DisplayPort is a relatively new industry standard for digital display technology. The advantages of DisplayPort overexisting technologies are: higher bandwidth for greater resolutions and color depths, bi-directional auxiliary
channel, variable interface width, and flexible power topologies, among others.
DisplayPort defines a high-speed main link carrying audio and video data, an auxiliary channel, and a hot-plug
detect signal. The main link is a unidirectional, high-bandwidth and low-latency channel. It consists of one, two, or
four AC-coupled differential pairs, called lanes. Version 1.1 of the standard defines two link rates: 1.62 and 2.7
Gbps. The lanes carry both data and an embedded clock at the link rate negotiated between Source and Sink,
independent of the resolution and color depth of the video stream. The link rate is de-coupled from the pixel rate,
resulting in a packetized stream. This differentiates DisplayPort from other digital video standards, like DVI/HDMI.
Due to the high link rate, the main link can only be implemented on dedicated gigabit transceiver pins of the Artix7 architecture.

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Nexys Video™ FPGA Board Reference Manual
The auxiliary channel is a bidirectional channel for link management and device control. It is AC-coupled, just likethe main link lanes, but uses a different encoding and the lower data rate of 1Mbps. Upon hot-plug detection, aSource will attempt to configure the link through link training. Handshaking link parameters happens via theauxiliary channel.
Nexys Video includes a Mini DisplayPort (mDP) connector wired in the Source role. The maximum lane countsupported is two. The two lanes of the main link are wired to the only gigabit transceiver bank: MGT bank 216.
Lane 0 is mapped to GTPE2_CHANNEL_X0Y4, while Lane 1 goes to GTPE2_CHANNEL_X0Y5. It is important to keep
in mind that bank 216, being the only one available in this FPGA package, is shared between the DisplayPort sourceand FMC ports. Depending on the exact application, simultaneous usage of the FMC gigabit lane and DisplayPort
might not be possible.
On-board there is a 135 MHz reference oscillator mapped to GTPE2_COMMON_X0Y1/MGTREFCLK1, which should
be used to generate the desired link rate. Refer to the Xilinx "7 Series FPGAs GTP Transceivers User Guide" (ug482)
for more information on how to implement high-speed interfaces.
The auxiliary channel is a bidirectional LVDS bus. Depending on the Xilinx tool/IP version, instantiating a differential
I/O buffer with LVDS signaling standard might not be possible. The work-around is to have two pairs of pins wired
and shorted together, as seen in Fig. 15. One pair should be implemented as input-only and the other as outputonly.
If the tool/IP allows bidirectional LVDS buffers, only one of the pairs needs to be used (it does not matter which),while the other declared as input and not used.
The hot-plug detect (HPD) signal connects to a general user I/O pin and should be configured as an input. It will beasserted when a sink is attached.

Lane 1MGTTXP/N1

Lane 0MGTTXP/N0
MGTREFCLK0P/N

Osc
135 MHzMGT 216

Artix-7

AA9
AB10
AA10
AA11
N15

mDP
AUX_P
AUX_N

HPD

Figure 14. DisplayPort wiring diagram.

The full implementation details of the DisplayPort standard is outside the scope of this document. Refer to the full
specifications published by VESA for more details.
Xilinx provides a fully documented Vivado IP core that implements a DisplayPort controller. Using this core will
greatly decrease the development required to get DisplayPort working on the Nexys Video. This core requires apaid license, but a 120 day evaluation license can be obtained for free from the Xilinx website.

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Other product and company names mentioned may be trademarks of their respective owners.

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Nexys Video™ FPGA Board Reference Manual

15

OLED

A Univision Technology Inc. UG-2832HSWEG04 is loaded on the Nexys Video. It is a white monochrome, 128 x 32,
0.91" organic LED display matrix bundled with a Solomon Systech SSD1306 display controller. The display datainterface towards the FPGA is a 4-wire serial peripheral interface (SPI). The 4 wires in controller-terminology are
CS#, D/C#, SDIN, and SCLK, but CS# is hard-wired to ground. This adds to the reset and two power control signals
for proper start-up sequencing. The signals are summarized in Table 12.
Signal
RES#
CS#
D/C#
SCLK
SDIN
VBAT#
VDD#

Description
Reset
Chip select (always active)
Data (high)/Command (low)Serial Clock
Serial Data
Power enable for internal power supply
Power enable for digital power

Polarity
Active-low
Active-low
BothActive-highActive-highActive-low
Active-low

FPGA pin
U21
N/A
W22
W21
Y22
P20
V22

Table 112. OLED signal description.

The serial interface is synchronous to SCLK and must conform to the timing specifications below. In most cases, a
10 MHz SCLK and data sent on the falling edge should work.

Figure 15. Serial interface timing diagram.

Figure 17. OLED serial interface bit ordering.
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Nexys Video™ FPGA Board Reference Manual
Symboltcycle
tAS
tAH
tCSS
tCSH
tDSW
tDHW
tCLKL
tCLKH
tR
tF

Parameter
Clock Cycle Time
Address Setup Time
Address Hold Time
Chip Select Setup Time
Chip Select Hold Time
Write Data Setup Time
Write Data Hold Time
Clock Low Time
Clock High Time
Rise Time
Fall Time

Min
100
15
15
20
10
15
15
20
20
-

Typ.
-

Max
40
40

Unit
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns

Table 13. Timing diagram symbols and parameters.

Start-up sequence:
1.
2.
3.
4.
5.
6.

Power up VDD by pulling OLED_VDD low. Wait 1ms.
Pulse RES# low for at least 3us.
Send initialization/configuration commands (see Table 12).
Power up VBAT by pulling OLED_VBAT low. Wait 100ms for voltage to stabilize.
Clear screen by writing zero to the display buffer.
Send "Display On" command (0xAF).
Command function
Charge pump enable
Set pre-charge period
Contrast control
Column inversion disable
Scan direction
COM pins configuration
Addressing mode: horizontal

Command bytes
0x8D, 0x14
0xD9, 0xF1
0x81, 0x0F
0xA0
0xC0
0xDA, 0x00
0x20

Table 12. OLED configuration commands.

After start-up, writing to the display is done by sending data bytes over the serial interface (D/C# high). Each data
bit corresponds to a pixel with the addressing mode, inversion, and scan direction settings determining exactly
which. Check out the Nexys Video Resource Center for reference projects that use the OLED.

16

Audio Codec

The Nexys Video board includes an Analog Devices ADAU1761 SigmaDSP audio codec (IC4) complementing its
multimedia features. Four 1/8" (3.5mm) audio jacks are available for line-out (J5-green), headphone-out (J3-black),line-in (J7-blue), and microphone-in (J6-pink). Each jack carries two channels of analog audio (stereo), with the
exception of the microphone input, which is mono.
To record or play back audio in an FPGA design, the audio data needs to be converted. The audio codec bridges thegap between the analog jacks and the digital FPGA pins. Analog-to-digital and digital-to-analog conversion is done
at up to 24 bits and 96 kHz sampling rate. Digital audio data is carried to/from the FPGA on a serial, full-duplex
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.

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Nexys Video™ FPGA Board Reference Manual2interface which supports several different formats, the default being I S. This interface is clocked by the FPGA
through BCLK by default, but the codec can be configured to provide the clock itself.
2

Configuring the audio codec can be done over I C. It responds to slave address 0b0111011, followed by a 16-bit
register address and one or more data bytes. These registers control every functional aspect of the codec.
The codec is clocked from the FPGA through the Master Clock (MCLK) pin. A clock must be provided for the codec2
to function, including the I C port. The exact frequency depends on the desired sample rate and whether PLL will
be used, but 12 MHz is a good start. The clocking infrastructure of a 7 series FPGA is more than capable ofsynthesizing the right frequency from the on-board 100 MHz reference oscillator.
For proper use, the concept of audio paths needs to be understood. There are two signal paths internal to thecodec: Playback and Record. Both are highly configurable analog paths with mixers and amplifiers that route audio
signals through the chip. The Playback path is the output path that routes audio from different sources, like thedigital-to-analog converter or input mixers towards the headphone and line-out jacks. On the other hand, therecord path routes audio from the line-in and microphone-in towards the analog-to-digital converters. Having
routing elements at every step enables signal mixing between channels, amplification, muting, and bypass.
However, it also means that each element has to be properly configured along the path.
Keep in mind that audio jack designations might differ from codec analog frontend designators. For example, theline-in jack connects to the AUX port of the codec. The microphone jack is wired to the IN port. Also, notice that
although some ports offer differential amplifiers and signaling, they are not used on the Nexys Video. For example,
the OUT port is differential, comprising 4 pins: LOUTP, LOUTN, ROUTP, and ROUTN. However, the N-side of thedifferential pairs is left floating, while the P-side connects to the jack.
At the very least, an audio-aware FPGA design should do the following:
1.
2.
3.

Provide MCLK for the audio codec.
2
Use an I C master controller to configure the core clocking, sample rates, serial interface format, andaudio path.
Send or receive audio samples over the serial audio data channel for playback or record.

A MicroBlaze-based reference project that uses the audio codec is available on the Nexys Video Resource Center.
More advanced users might want to try additional features of the ADAU1761. For example, the on-chip SigmaDSP
core can be programmed to do user-defined digital signal processing. All relevant information can be found in the
ADAU1761 data sheet.

Artix-7

T4
W6
T5
U5
U6
V5
W5

ADC_SDATADAC_SDATA
BCLK
LRCLK
MCLK
SDA
SCL

L/RHP

Headphone Out

L/ROUTPLine Out

L/RAUXLine In

L/RINN

Microphone In

ADAU1761

Figure 16. Audio signal connections.
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.

Page 27 of 28

Nexys Video™ FPGA Board Reference Manual
Signal NameFPGA Pin

Pin Function

ADC_SDATA

T4

Serialized audio resulting from the analog-to-digital conversion (record).

DAC_SDATA

W6

Serialized audio is converted to analog by the codec (playback).

BCLK

T5

Serial data port clock.

LRCLK

U5

Serial data port frame clock.

MCLK

U6

Master clock.

SDA

V5

I C configuration interface.

SCL

W5

I C configuration interface.

2
2

Table 13. Audio signal description.

17

Out-of-box Demo

The Nexys Video comes with an out-of-box demo design that gets loaded from the on-board Quad SPI flash. It
exercises most of the on-board peripherals. Follow the instructions to explore them all:
•
•
•
•
•
•
•

•

Connecting an HDMI/DVI or DisplayPort monitor shows a test pattern with a mouse pointer.
Connecting a USB mouse controls the mouse pointer on the display.
Connecting an HDMI/DVI source, like a laptop output, replaces the test pattern with the source image.
Connecting the board to an Ethernet network will acquire link, IP address, and become "pingable" at the
IPv4 address displayed on the OLED.
The internal XADC temperature is read and shown on the OLED.
Connecting the USB-UART port to a PC and opening a terminal (115200,8,N,1) shows status messages.
Pushing BTNU records audio off the microphone input for five seconds and plays it back on theheadphone output if BTND is pushed, or line-out if BTNL. Similarly, BTNR starts a recording off the line-injack.
Slide switches are wired to the LEDs above.

The source code for this design is available on the Nexys Video Resource Center.

Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.

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