DS2422/DS2423
1kbit/4kbit 1-Wire
RAM with Counter
www.maxim-ic.com

FEATURES
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4096 bits of SRAM (DS2423), 1024 bits with
the DS2422
Four 32-bit, read-only counters (DS2423),
three counters with the DS2422
Active-low external trigger inputs for two of
the counters with on-chip debouncing
compatible with reed and Wiegand switches
Unique, factory-lasered and tested 64-bit
registration number (8-bit family code + 48bit serial number + 8-bit CRC tester) assuresabsolute traceability because no two parts are
alike
Memory partitioned into 16 256-bit pages inDS2423 (4 pages in DS2422) for packetizing
data
256-bit scratchpad with strict read/write
protocols ensures integrity of data transfer
On-chip 16-bit CRC generator forsafeguarding data transfers
Built-in multidrop controller ensurescompatibility with other MicroLAN products
Directly connects to a single port pin of a
microprocessor and communicates at up to
16.3kbits per second
Overdrive mode boosts communication speed
to 142kbits per second
8-bit family code specifies device
communication requirements to reader§§§

Presence detector acknowledges when reader
first applies voltage
Compact, low cost 6-pin TSOC surface mountpackage
Reads, writes and counts over a wide voltage
range of 2.8V to 5.5V from -40°C to +85°C

PIN ASSIGNMENT
TSOC PACKAGE
1
2
3

6
5
4

TOP VIEW
3.7mm x 4.0mm x 1.5mm

SIDE VIEWPIN DESCRIPTION
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6

GroundData
Vbat
NC
Input channel B
Input channel A

ORDERING INFORMATION
DS2423P
DS2423P/T&R
DS2423X
DS2422P

6-pin TSOC package
Tape & Reel Version of
DS2423P
Chip Scale Pkg., Tape &ReelContact Factory

DESCRIPTION

The DS2422/DS2423 1-Wire® RAM with Counters (hereafter referred to as DS242X) is a fully static,
read/write memory for battery operation in a low-cost, six-lead TSOC, surface-mount package. The
memory is organized as 16 pages (DS2423) or four pages (DS2422) of 256 bits each. In addition, thedevice has four (DS2423) or three (DS2422) counters, two of them with external trigger inputs called A
and B. Each of the counters is associated with a memory page. A counter without external trigger input
increments each time data is written to the page it is associated with (write cycle counter). The counters
1-Wire is a registered trademark of Dallas Semiconductor.

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DS2422/DS2423

triggered by inputs A and B, respectively, increment with every low-going pulse on their input. All
counters are read-only. They are automatically cleared to 0 when the battery is connected.
The battery-backed memory offers a simple solution to storing and retrieving information pertaining to
the equipment where the DS242X is installed and its frequency of use. The scratchpad is an additional
page that acts as a buffer when writing to memory. Data is first written to the scratchpad where it may beread back for verification. A copy scratchpad command will then transfer the data to memory. This
process ensures data integrity when modifying the memory. A 64-bit registration number is factory
lasered into each DS242X to provide a guaranteed unique identity which allows for absolute traceability
and acts as node address if multiple DS242X are connected in parallel to form a local network. Data istransferred serially via the 1-Wire protocol which requires only a single data lead and a ground return.
The DS242X 1-Wire RAM with Counters can store encrypted data. The unique registration number andthe page write cycle counter(s) prevent unauthorized manipulation of data stored in a page with a write
cycle counter associated.

OVERVIEWThe block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS242X. The DS242X has four main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad,
3) 1024-bit (DS2422) or 4096-bit (DS2423) SRAM, and 4) three (DS2422) or four (DS2423) 32-bit readonly counters. The hierarchical structure of the 1-Wire protocol is shown in Figure 2. Each of thesecounters is associated with one of the 256-bit memory pages. The three counters of the DS2422 areassociated with pages 1 to 3; the four counters of the DS2423 are associated with pages 12 to 15. The
contents of the counter is read together with the memory data using a special command. The bus mastermust first provide one of the six ROM Function Commands: 1) Read ROM, 2) Match ROM, 3) Search
ROM, 4) Skip ROM, 5) Overdrive-Skip ROM or 6) Overdrive-Match ROM. Upon completion of an
Overdrive ROM command byte executed at standard speed, the device will enter Overdrive mode where
all subsequent communication occurs at a higher speed. The protocol required for these ROM functioncommands is described in Figure 9. After a ROM function command is successfully executed, thememory functions become accessible and the master may provide any one of the five memory functioncommands. The protocol for these memory function commands is described in Figure 7. All data is read
and written least significant bit first.

PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry steals power whenever
the I/O input is high. I/O will provide sufficient power as long as the specified timing and voltage
requirements are met. The advantages of parasite power are two-fold: 1) by parasiting off this input,
lithium is conserved, and 2) if the battery is exhausted for any reason, the ROM may still be readnormally.

64-BIT LASERED ROM
Each DS242X contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.
The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits (See Figure 3).
The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gatesas shown in Figure 4. The polynomial is X8 + X5 + X4 + 1. Additional information about the Dallas 1Wire Cyclic Redundancy Check is available in the Book of DS19xx iButton® Standards.
The shift register bits are initialized to 0. Then starting with the least significant bit of the family code,
one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number
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iButton is a registered trademark of Dallas Semiconductor.

DS2422/DS2423

is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC
value. Shifting in the 8 bits of CRC should return the shift register to all 0s.

BLOCK DIAGRAM Figure 1

MEMORYThe memory map in Figure 5 shows a 32-byte page called the scratchpad and an additional 32-byte pages
called memory. The DS2422 contains pages 0 through 3 that make up the 1024-bit SRAM. The DS2423
contains pages 0 through 15 that make up the 4096-bit SRAM. The scratchpad is an additional page thatacts as a buffer when writing to memory.

ADDRESS REGISTERS AND TRANSFER STATUS
Because of the serial data transfer, the DS242X employs three address registers called TA1, TA2, and E/S(Figure 6). Registers TA1 and TA2 must be loaded with the target address to which the data will be
written or from which data will be sent to the master upon a Read command. Register E/S acts like a byte
counter and Transfer Status register. It is used to verify data integrity with write commands. Therefore,
the master only has read access to this register. The lower 5 bits of the E/S register indicate the address of
the last byte that has been written to the scratchpad. This address is called Ending Offset. Bit 5 of the E/Sregister, called PF or “partial byte flag,” is set if the number of data bits sent by the master is not an
integer multiple of 8. Bit 6 has no function; it always reads 0. Note that the lowest 5 bits of the target
address also determine the address within the scratchpad, where intermediate storage of data will begin.
This address is called byte offset. If the target address (TA1) for a Write command is 03CH for example,
then the scratchpad will store incoming data beginning at the byte offset 1CH and will be full after only 4
bytes. The corresponding ending offset in this example is 1FH. For best economy of speed and efficiency,
the target address for writing should point to the beginning of a new page, i.e., the byte offset will be 0.
Thus the full 32-byte capacity of the scratchpad is available, resulting also in the ending offset of 1FH.
However, it is possible to write one or several contiguous bytes somewhere within a page. The ending
offset together with the Partial Flag support the master checking the data integrity after a Write command.
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DS2422/DS2423

The highest valued bit of the E/S register, called AA or Authorization Accepted, acts as a flag to indicatethat the data stored in the scratchpad has already been copied to the target memory address. Writing data
to the scratchpad clears this flag.

HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2

64-BIT LASERED ROM Figure 3MSB

LSB
8-BIT CRC CODE

MSB

8-BIT FAMILY CODE
(1CH = DS2422,
1DH = DS2423)

48-BIT SERIAL NUMBER
LSB

MSB

LSB

1-WIRE CRC GENERATOR Figure 4

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MSB

LSB

DS2422/DS2423

WRITING WITH VERIFICATION
To write data to the DS242X, the scratchpad has to be used as intermediate storage. First the masterissues the Write Scratchpad command to specify the desired target address, followed by the data to be
written to the scratchpad. Under certain conditions (see Write Scratchpad command) the master will
receive an inverted CRC16 of the command, address and data at the end of the Write Scratchpad
command sequence. Knowing this CRC value, the master can compare it to the value it has calculated
itself to decide if the communication was successful and proceed to the Copy Scratchpad command. If themaster could not receive the CRC16, it has to send the Read Scratchpad command to read back thescratchpad to verify data integrity. As preamble to the scratchpad data, the DS242X repeats the target
address TA1 and TA2 and sends the contents of the E/S register. If the PF flag is set, data did not arrive
correctly in the scratchpad. The master does not need to continue reading; it can start a new trial to write
data to the scratchpad. Similarly, a set AA flag indicates that the Write command was not recognized by
the device. If everything went correctly, both flags are cleared and the ending offset indicates the addressof the last byte written to the scratchpad. Now the master can continue reading and verifying every databyte. After the master has verified the data, it has to send the Copy Scratchpad command. This commandmust be followed exactly by the data of the three address registers TA1, TA2 and E/S. The master may
obtain the contents of these registers by reading the scratchpad or derive it from the target address and theamount of data to be written. As soon as the DS242X has received these bytes correctly, it will copy thedata to the requested location beginning at the target address.

MEMORY FUNCTION COMMANDSThe Memory Function Flow Chart (Figure 7) describes the protocols necessary for accessing the memory.
An example follows the flowchart. The communication between master and DS242X takes place either atregular speed (default, OD = 0) or at Overdrive speed (OD = 1). If not explicitly set into the Overdrivemode the DS242X assumes regular speed.

Write Scratchpad Command [0FH]
After issuing the Write Scratchpad command, the master must first provide the 2-byte target address,
followed by the data to be written to the scratchpad. The data will be written to the scratchpad starting at
the byte offset (T4:T0). The ending offset (E4: E0) will be the byte offset at which the master stops
writing data. Only full data bytes are accepted. If the last data byte is incomplete its content will beignored and the partial byte flag PF will be set.
When executing the Write Scratchpad command the CRC generator inside the DS242X (see Figure 12)
calculates a CRC over the entire data stream, starting at the command code and ending at the last databyte sent by the master. This CRC is generated using the CRC16 polynomial by first clearing the CRC
generator and then shifting in the command code (0FH) of the Write Scratchpad command, the Target
Addresses TA1 and TA2 as supplied by the master and all the data bytes. The master may end the Write
Scratchpad command at any time. However, if the ending offset is 11111b, the master may send 16 readtime slots and will receive the CRC generated by the DS242X.
The memory address range of the DS2422 is 0000H to 007FH and 0000H to 01FFH for the DS2423,
respectively. If the bus master sends a target address higher than this, the internal circuitry of the chip
will set the nine (DS2422) or seven (DS2423) most significant address bits to 0 as they are shifted into
the internal address register. The Read Scratchpad command will reveal the target address as it will be
used by the DS242X. The master will identify such address modifications by comparing the target
address read back to the target address transmitted. If the master does not read the scratchpad, asubsequent Copy Scratchpad command will not work since the most significant bits of the target address
the master sends will not match the value the DS242X expects.
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DS2422/DS2423

Read Scratchpad Command [AAH]This command is used to verify scratchpad data and target address. After issuing the Read Scratchpad
command, the master begins reading. The first 2 bytes will be the target address. The next byte will be theending offset/data status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4: T0).
The master may read data until the end of the scratchpad after which the data read will be all logic 1s.

Copy Scratchpad [5AH]
This command is used to copy data from the scratchpad to memory. After issuing the Copy Scratchpad
command, the master must provide a 3-byte authorization pattern which can be obtained by reading thescratchpad for verification. This pattern must exactly match the data contained in the three address
registers (TA1, TA2, E/S, in that order). If the pattern matches, the AA (Authorization Accepted) flag
will be set and the copy will begin. A pattern of alternating 1s and 0s will be transmitted after the data has
been copied until a Reset Pulse is issued by the master. Any attempt to reset the part will be ignored while
the copy is in progress. Copy typically takes 30µs. The data to be copied is determined by the threeaddress registers. The scratchpad data from the beginning offset through the ending offset will be copied
to memory, starting at the target address. Anywhere from 1 to 32 bytes may be copied to memory withthis command. The AA flag will be cleared only by executing a Write Scratchpad command.

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DS2422/DS2423

DS242X MEMORY MAP Figure 5

ADDRESS REGISTERS Figure 6

Read Memory [F0H]
The read memory command may be used to read the entire memory. After issuing the command, themaster must provide the 2-byte target address. After the two bytes, the master reads data beginning fromthe target address and may continue until the end of memory, at which point logic 1s will be read. It is
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DS2422/DS2423

important to realize that the target address registers will contain the address provided. The ending
offset/data status byte is unaffected.
The hardware of the DS242X provides a means to accomplish error-free writing to the memory section.
To safeguard reading data in the 1-Wire environment and to simultaneously speed up data transfers, it isrecommended to packetize data into data packets of the size of one memory page each. Such a packet
would typically store a 16-bit CRC with each page of data to ensure rapid, error-free data transfers thateliminate having to read a page multiple times to determine if the received data is correct or not. (See theBook of DS19xx iButton Standards, Chapter 7 for the recommended file structure.)

Read Memory + Counter [A5H]
The Read Memory + Counter command is used to read memory data together with the write cycle counteror externally triggered counter associated with the addressed page of data memory. The additional
information is transmitted by the DS242X as the end of a memory page is encountered. Following thecurrent value of the counter the DS242X transmits 32 0-bits and a 16-bit CRC generated by the DS242X.
After having sent the command code of the Read Memory + Counter command, the bus master sends a
two-byte address (TA1 = (T7:T0), TA2 = (T15:T8)) that indicates a starting byte location within the data
field. With the subsequent read data time slots the master receives data from the DS242X starting at theinitial address and continuing until the end of a 32-byte page is reached. At that point the bus master will
send 80 additional read data time slots and receive the contents of the 32-bit counter associated with theaddressed page, 32 0-bits and a 16-bit CRC. With subsequent read data time slots the master will receive
data starting at the beginning of the next page followed by the contents of the counter associated with thepage, 0-bits and CRC for that page. This sequence will continue until the final page and its accompanying
data is read by the bus master. When applying the Read Memory + Counter command to a page that does
not have a counter associated, the master will read FFFFFFFFH instead of a valid count.
With the initial pass through the Read Memory + Counter flow chart the 16-bit CRC value is the result ofshifting the command byte into the cleared CRC generator, followed by the two address bytes, thecontents of the data memory, the counter and the 0-bits. Subsequent passes through the Read Memory +Counter flow chart will generate a 16-bit CRC that is the result of clearing the CRC generator and thenshifting in the contents of the data memory page, its associated counter and 0-bits. After the 16-bit CRC
of the last page is read, the bus master will receive logical 1s from the DS242X until a Reset Pulse isissued. The Read Memory + Counter command sequence can be ended at any point by issuing a Reset
Pulse.

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DS2422/DS2423

MEMORY FUNCTION FLOW CHART Figure 7

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DS2422/DS2423

MEMORY FUNCTION FLOW CHART Figure 7 cont’d

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DS2422/DS2423

MEMORY FUNCTION FLOW CHART Figure 7 cont’d

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DS2422/DS2423

MEMORY FUNCTION EXAMPLE (DS2423)
Example: Write two data bytes to memory location 0026 and 0027. Read entire memory.
MASTER MODE
TX
RX
TX
TX
TX
TX
TX
TX
RX
TX
TX
RX
RX
RX
RX
TX
RX
TX
TX
TX
TX
TX
TX
RX
TX
TX
TX
TX
RX
TX
RX

DATA (LSB FIRST)
Reset
Presence
CCh
0Fh
26h
00h
<2 data bytes>
Reset
Presence
CCh
AAh
26h
00h
07h
<2 data bytes>
Reset
Presence
CCh
5Ah
26h
00h
07h
Reset
Presence
CCh
F0h
00h
00h
<512 bytes>
Reset
Presence

COMMENTS
Reset pulse (480-960 µs)
Presence pulse
Issue “skip ROM” command
Issue “write scratchpad” command
TA1, beginning offset=26h
TA2, address=0026h
Write 2 bytes of data to scratchpad
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “read scratchpad” command
Read TA1, beginning offset=26h
Read TA2, address=0026h
Read E/S, ending offset=7h, flags=0h
Read scratchpad data and verify
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “copy scratchpad” command
TA1
TA2
AUTHORIZATION CODE
E/S
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “read memory” command
TA1, beginning offset=0
TA2, address=0000h
Read entire memory
Reset pulse
Presence pulse, done

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DS2422/DS2423

MEMORY FUNCTION EXAMPLE (DS2423)
Read page 14 and counts of Input A. Rewrite page 14 with 32 bytes. Read Memory + Counter, Write
Scratchpad, Copy Scratchpad.
MASTER MODE
TX
RX
TX
TX
TX
TX
RX
RX
RX
RX
TX
RX
TX
TX
TX
TX
TX
RX
TX
RX
TX
TX
TX
TX
TX
RX
TX
RX

DATA (LSB FIRST)
Reset
Presence
CCh
A5h
C0h
01h
<32 data bytes><4 data bytes><4 data bytes><2 data bytes>
Reset
Presence
CCh
0Fh
C0h
01h
<32 data bytes><2 data bytes>
Reset
Presence
CCh
5Ah
C0h
01h
1Fh
<1 data byte>
Reset
Presence

COMMENTS
Reset pulse (480-960 µs)
Presence pulse
Issue “skip ROM” command
Issue “read memory + counter” command
TA1, beginning offset=C0h
TA2, address=01C0h
Read 32 bytes of data
Read Counts of Input A
Read 32 Zero Bits
Read (inverted) CRC16
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “write scratchpad” command
TA1, beginning offset=C0h
TA2, address=01C0h
Read 32 bytes of data to scratchpad
Read (inverted) CRC16
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “copy scratchpad” command
TA1
TA2
AUTHORIZATION CODE
E/S
Read Copy Scratchpad response
Reset pulse
Presence pulse, done

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DS2422/DS2423

HARDWARE CONFIGURATION Figure 8

RPU

Note: Depending on the 1-Wire communication speed and the bus load characteristics, the optimal pullup resistor (RPU) value will be in the 1.5kW to 5kW range.

1-WIRE BUS SYSTEM
The 1-Wire bus is a system which has a single bus master and one or more slaves. In all instances theDS242X is a slave device. The bus master is typically a microcontroller. The discussion of this bus
system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wiresignaling (signal types and timing). A 1-Wire protocol defines bus transactions in terms of the bus state
during specific time slots that are initiated on the falling edge of sync pulses from the bus master. For a
more detailed protocol description, refer to Chapter 4 of the Book of DS19xx iButton Standards.

HARDWARE CONFIGURATION
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able todrive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have opendrain or 3-state outputs. The 1-Wire port of the DS242X is open drain with an internal circuit equivalent
to that shown in Figure 8. A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At
regular speed the 1-Wire bus has a maximum data rate of 16.3kbits per second. The speed can be boosted
to 142kbits per second by activating the Overdrive mode. The 1-Wire bus requires a pullup resistor of
approximately 5kΩ. The 1-Wire bus requires a pullup resistor range of 1.5kW to 5kW, depending on thebus load characteristics.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus
MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low
for more than 16µs (Overdrive speed) or more than 120µs (regular speed), one or more devices on the bus
may be reset.

TRANSACTION SEQUENCE
The protocol for accessing the DS242X via the 1-Wire port is as follows:§

Initialization§

ROM Function Command§

Memory Function Command§

Transaction/Data
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DS2422/DS2423

INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a Reset Pulse transmitted by the bus master followed by Presence Pulse(s) transmitted by theslave(s).
The Presence Pulse lets the bus master know that the DS242X is on the bus and is ready to operate. For
more details, see the 1-Wire Signaling section.

ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the six ROM function commands. All
ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure
9):

Read ROM [33H]
This command allows the bus master to read the DS242X’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command can only be used if there is a single DS242X on the bus. If morethan one slave is present on the bus, a data collision will occur when all slaves try to transmit at the sametime (open drain will produce a wired-AND result). The resultant family code and 48-bit serial number
will result in a mismatch of the CRC.

Match ROM [55H]
The match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a
specific DS242X on a multidrop bus. Only the DS242X that exactly matches the 64-bit ROM sequence
will respond to the following memory function command. All slaves that do not match the 64-bit ROM
sequence will wait for a Reset Pulse. This command can be used with a single or multiple devices on thebus.

Skip ROM [CCH]This command can save time in a single-drop bus system by allowing the bus master to access thememory functions without providing the 64-bit ROM code. If more than one slave is present on the bus
and a read command is issued following the Skip ROM command, data collision will occur on the bus asmultiple slaves transmit simultaneously (open drain pulldowns will produce a wired-AND result).

Search ROM [F0H]
When a system is initially brought up, the bus master might not know the number of devices on the 1Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a processof elimination to identify the 64-bit ROM codes of all slave devices on the bus. The search ROM process
is the repetition of a simple, three-step routine: read a bit, read the complement of the bit, then write thedesired value of that bit. The bus master performs this simple, three-step routine on each bit of the ROM.
After one complete pass, the bus master knows the contents of the ROM in one device. The remaining
number of devices and their ROM codes may be identified by additional passes. See Chapter 5 of theBook of DS19xx iButton Standards for a comprehensive discussion of a search ROM, including an actual
example.

Overdrive Skip ROM [3CH]On a single-drop bus this command can save time by allowing the bus master to access the memory
functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command the Overdrive
Skip ROM sets the DS242X in the Overdrive mode (OD = 1). All communication following thiscommand has to occur at Overdrive speed until a Reset Pulse of minimum 480µs duration resets all
devices on the bus to regular speed (OD = 0).
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DS2422/DS2423

When issued on a multidrop bus this command will set all Overdrive-supporting devices into Overdrive
mode. To subsequently address a specific Overdrive-supporting device, a Reset Pulse at Overdrive speed
has to be issued followed by a Match ROM or Search ROM command sequence. This will speed up thetime for the search process. If more than one slave supporting Overdrive is present on the bus and theOverdrive Skip ROM command is followed by a read command, data collision will occur on the bus asmultiple slaves transmit simultaneously (open drain pulldowns will produce a wired-AND result).

Overdrive Match ROM [69H]
The Overdrive Match ROM command, followed by a 64-bit ROM sequence transmitted at Overdrive
speed, allows the bus master to address a specific DS242X on a multidrop bus and to simultaneously set itin Overdrive mode. Only the DS242X that exactly matches the 64-bit ROM sequence will respond to thesubsequent memory function command. Slaves already in Overdrive mode from a previous Overdrive
Skip or Match command will remain in Overdrive mode. All other slaves that do not match the 64-bit
ROM sequence or do not support Overdrive will return to or remain at regular speed and wait for a Reset
Pulse of minimum 480 µs duration. The Overdrive Match ROM command can be used with a single ormultiple devices on the bus.

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DS2422/DS2423

ROM FUNCTIONS FLOW CHART Figure 9 (First Part)

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DS2422/DS2423

ROM FUNCTIONS FLOW CHART Figure 9 cont’d

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DS2422/DS2423

1-WIRE SIGNALINGThe DS242X requires strict protocols to ensure data integrity. The protocol consists of four types ofsignaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1 and Read
Data. The bus master initiates all these signals except Presence Pulse. The DS242X can communicate at
two different speeds, regular speed and Overdrive speed. If not explicitly set into the Overdrive mode, theDS242X will communicate at regular speed. While in Overdrive mode the fast timing applies to all
waveforms.
The initialization sequence required to begin any communication with the DS242X is shown in Figure 10.
A Reset Pulse followed by a Presence Pulse indicates the DS242X is ready to send or receive data given
the correct ROM command and memory function command. The bus master transmits (TX) a Reset
Pulse (tRSTL, minimum 480 µs at regular speed, 48 µs at Overdrive speed). The bus master then releases
the line and goes into receive mode (RX). The 1-Wire bus is pulled to a high state via the pullup resistor.
After detecting the rising edge on the data pin, the DS242X waits (tPDH, 15-60µs at regular speed, 2-6µs
at Overdrive speed) and then transmits the Presence Pulse (tPDL, 60-240µs at regular speed, 8-24µs at
Overdrive speed).
A Reset Pulse of 480µs or longer will exit the Overdrive mode returning the device to regular speed. If
the DS242X is in Overdrive mode and the Reset Pulse is no longer than 80µs the device will remain in
Overdrive mode.

Read/Write Time Slots
The definitions of write and read time slots are illustrated in Figure 11. All time slots are initiated by themaster driving the data line low. The falling edge of the data line synchronizes the DS242X to the masterby triggering a delay circuit in the DS242X. During write time slots, the delay circuit determines when
the DS242X will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay
circuit determines how long the DS242X will hold the data line low overriding the 1 generated by themaster. If the data bit is a “1”, the device will leave the read data time slot unchanged.

INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 10

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DS2422/DS2423

READ/WRITE TIMING DIAGRAM Figure 11

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DS2422/DS2423

CRC GENERATIONWith the DS242X there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is an 8bit type and is stored in the most significant byte of the 64-bit ROM. The bus master can compute a CRC
value from the first 56 bits of the 64-bit ROM and compare it to the value stored within the DS242X todetermine if the ROM data has been received error-free by the bus master. The equivalent polynomial
function of this CRC is: X8 + X5 + X4 + 1. This 8-bit CRC is received in the true (non-inverted) form
when reading the ROM of the DS242X. It is computed at the factory and lasered into the ROM.
The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function x16+ x15 + x2 + 1. This CRC is used for error detection when reading Data Memory using the Read Memory+ Counter command and for fast verification of a data transfer when writing to the scratchpad. It is thesame type of CRC as is used with NV RAM based iButtons for error detection within the iButton
Extended File Structure. In contrast to the 8-bit CRC, the 16-bit CRC is always returned or sent in thecomplemented (inverted) form. A CRC-generator inside the DS242X chip (Figure 12) will calculate a
new 16-bit CRC as shown in the command flow chart of Figure 7. The bus master compares the CRC
value read from the device to the one it calculates from the data and decides whether to continue with anoperation or re-read the portion of the data with the CRC error.
With the initial pass through the Read Memory + Counter flow chart the 16-bit CRC value is the result ofshifting the command byte into the cleared CRC generator, followed by the two address bytes, data bytes,
value of the counter associated with the page and zero bits. Subsequent passes through the Read Memory+ Counter flow chart will generate a 16-bit CRC that is the result of clearing the CRC generator and thenshifting in the data bytes, the value of the counter and the zero bits.
With the Write Scratchpad command the CRC is generated by first clearing the CRC generator and thenshifting in the command code, the Target Addresses TA1 and TA2 and all the data bytes. The DS242X
will transmit this CRC only if the data bytes written to the scratchpad include scratchpad ending offset
11111b. The data may start at any location within the scratchpad.
For more details on generating CRC values including example implementations in both hardware andsoftware, see the Book of DS19xx iButton Standards.
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DS2422/DS2423

CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL Figure 12

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DS2422/DS2423

ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground
Operating Temperature Range
Storage Temperature Range
Soldering Temperature*-0.5V to +7.0V-40°C to +85°C-55°C to +125°C
See J-STD-020A Specifications

This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.

DC CHARACTERISTICS (VPUP = 2.8V to 6.0V; VBAT = 2.8 to 5.5V;-40°C to +85°C)
PARAMETER
Logic 1
Logic 0
Output Logic Low @ 4 mA
Output Logic High
Input Load Current
Standby Current
I/O Operate Charge

SYMBOL
VIH
VIL
VOL
VOH
IL
IBATS
QBATO

MIN
2.2
-0.3

TYP

VPUP
5

MAX
+0.8
0.4
6.0
200
200

UNITS
V
V
V
V
µA
nA
nC

CAPACITANCE
PARAMETER
I/O (1-Wire)

NOTES
1, 8
1, 9
1
1, 2
3
12

(tA = 25°C)
SYMBOL
CIN/OUT

MIN

TYP
100

MAX
800

UNITS
pF

NOTES
6

COUNTER INPUT CHARACTERISTICS(VPUP = 2.8V to 6.0V; VBAT = 2.8 to 5.5V;-40°C to +85°C)
PARAMETERSYMBOL

MIN

Trip Point

VTRIP

Logic 1

VINH

VTRIP

Logic 0Internal Pullup Resistor
Debounce Time
Pulse Width (Active Low)

VINL
RPI
TDEB
TPW

-0.3

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170
1

TYP
½
VBAT

MAX

NOTES

V
VBAT
+0.3
VTRIP

28
290

UNITS

460

V

1, 10

V
MV
µs
µs

1
11
13

DS2422/DS2423

AC CHARACTERISTICS REGULAR SPEED(VPUP = 2.8V to 6.0V; VBAT = 2.8 to 5.5V;-40°C to +85°C)
PARAMETERTime Slot
Write 1 Low Time
Write 0 Low Time
Read Low Time
Read Data Valid
Release Time
Read Data Setup
Recovery Time
Reset Time HighReset Time Low
Presence Detect High
Presence Detect Low

SYMBOL
tSLOT
tLOW1
tLOW0
tLOWR
tRDV
tRELEASE
tSU
tREC
tRSTH
tRSTL
tPDH
tPDL

MIN
60
1
60
1
0

TYP

15
15

1
480
480
15
60

MAX
120
15
120
15
45
1
960
60
240

UNITS
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs

NOTES
15
15
14
5
4
7

AC CHARACTERISTICS OVERDRIVE SPEED(VPUP = 2.8V to 6.0V; VBAT = 2.8 to 5.5V;-40°C to +85°C)
PARAMETERTime Slot
Write 1 Low Time
Write 0 Low Time
Read Low Time
Read Data Valid
Release Time
Read Data Setup
Recovery Time
Reset Time HighReset Time Low
Presence Detect High
Presence Detect Low

SYMBOL
tSLOT
tLOW1
tLOW0
tLOWR
tRDV
tRELEASE
tSU
tREC
tRSTH
tRSTL
tPDH
tPDL

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MIN
6
1
6
1
0
1
48
48
2
8

TYP

2
1.5

MAX
16
2
16
2
4
1
80
6
24

UNITS
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs

NOTES
15
15
14
5
4

DS2422/DS2423

NOTES:
1) All voltages are referenced to ground.
2) VPUP = external pullup voltage.
3) Input load is to ground.
4) An additional reset or communication sequence cannot begin until the reset high time has expired.
5) Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data isguaranteed to be valid within 1µs of this falling edge.
6) Capacitance on the data pin could be 800pF when power is first applied. If a 5kΩ resistor is used topull up the data line to VPUP, 5µs after power has been applied the parasite capacitance will not affectnormal communications.
7) The reset low time (tRSTL) should be restricted to a maximum of 960µs, to allow interrupt signaling,otherwise, it could mask or conceal interrupt pulses.
8) VIH is a function of the external pullup resistor and VPUP.
9) Under certain low voltage conditions VILMAX may have to be reduced to as much as 0.5V to always
guarantee a Presence Pulse.
10) The counter inputs are designed for interfacing to mechanical switches and piezo sensors. If
interfacing to digital circuits, one should use an open drain driver.
11) A lower impedance pullup, e. g., for reed switches, can be achieved by connecting an external resistor
from the counter input to VBAT.
12) Read and write scratchpad (all 32 bytes) at VBAT of 3.0 V.
13) Each low-going edge on a counter input resets the channel’s debounce timer. The debounce time
starts as the input voltage rises beyond the trip point. In order for the next pulse to be counted thedebounce time must have expired.
14) The optimal sampling point for the master is as close as possible to the end time of the tRDV period
without exceeding tRDV. For the case of a Read-One Time slot, this maximizes the amount of time forthe pullup resistor to recover to a high level. For a Read-Zero Time slot, it ensures that a read will
occur before the fastest 1-Wire device(s) releases the line.
15) The duration of the low pulse sent by the master should be a minimum of 1µs with a maximum value
as short as possible to allow time for the pullup resistor to recover the line to a high level before the 1Wire device samples in the case of a Write-One Time or before the master samples in the case of a
Read-One Time.

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