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060603

FEATURES

§ 4096 bits of SRAM

§ Four 32-bit, read-only counters

§ 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 + 48-
bit serial number + 8-bit CRC tester) assures
absolute traceability because no two parts are
alike

§ Memory partitioned into 16 256-bit pages in

for packetizing data

§ 256-bit scratchpad with strict read/write

protocols ensures integrity of data transfer

§ On-chip 16-bit CRC generator for

safeguarding data transfers

§ Built-in multidrop controller ensures

compatibility 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 mount

package

§ Reads, writes and counts over a wide voltage

range of 2.8V to 5.5V from -40°C to +85°C

PIN ASSIGNMENT

PIN DESCRIPTION

Pin 1

Ground

Pin 2

Data

Pin 3

Vbat

Pin 4

Pin 5

Input channel B

Pin 6

Input channel A

ORDERING INFORMATION

DS2423P

6-pin TSOC package

DS2423P/T&R

Tape & Reel Version of
DS2423P

DS2423X

Chip Scale Pkg., Tape &
Reel

DESCRIPTION

The DS2423 1-Wire

RAM with Counters 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 of 256 bits each.
In addition, the device has four 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 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.

DS2423

4kbit 1-Wire

RAM with Counter

www.maxim-ic.com

2
3

5
4

TOP VIEW

3.7mm x 4.0mm x 1.5mm

SIDE VIEW

TSOC PACKAGE

1-Wire is a registered trademark of Dallas Semiconductor.

DS2423

2 of 25

The battery-backed memory offers a simple solution to storing and retrieving information pertaining to
the equipment where the DS2423 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 be
read 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 DS2423 to provide a guaranteed unique identity which allows for absolute traceability
and acts as node address if multiple DS2423 are connected in parallel to form a local network. Data is
transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return.

The DS2423 1-Wire RAM with Counters can store encrypted data. The unique registration number and
the page write cycle counter(s) prevent unauthorized manipulation of data stored in a page with a write
cycle counter associated.

OVERVIEW

The block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS2423. The DS2423 has four main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad,
3) 4096-bit SRAM, and 4) four 32-bit read-only counters. The hierarchical structure of the 1-Wire
protocol is shown in Figure 2. Each of these counters is associated with one of the 256-bit memory pages.
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 master must 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 function commands is
described in Figure 9. After a ROM function command is successfully executed, the memory functions
become accessible and the master may provide any one of the five memory function commands. 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 read
normally.

64-BIT LASERED ROM

Each DS2423 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 gates
as shown in Figure 4. The polynomial is X

+ X

+ 1. Additional information about the Dallas 1-

Wire 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 8

bit of the family code has been entered, then the serial number

is entered. After the 48

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.

iButton is a registered trademark of Dallas Semiconductor.

DS2423

3 of 25

BLOCK DIAGRAM Figure 1

ADDRESS REGISTERS AND TRANSFER STATUS

Because of the serial data transfer, the DS2423 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/S
register, 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.
The highest valued bit of the E/S register, called AA or Authorization Accepted, acts as a flag to indicate
that the data stored in the scratchpad has already been copied to the target memory address. Writing data
to the scratchpad clears this flag.

DS2423

5 of 25

WRITING WITH VERIFICATION

To write data to the DS2423, the scratchpad has to be used as intermediate storage. First the master issues
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 the master
could not receive the CRC16, it has to send the Read Scratchpad command to read back the scratchpad to
verify data integrity. As preamble to the scratchpad data, the DS2423 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 address of the last
byte written to the scratchpad. Now the master can continue reading and verifying every data byte. After
the master has verified the data, it has to send the Copy Scratchpad command. This command must 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 the amount of
data to be written. As soon as the DS2423 has received these bytes correctly, it will copy the data to the
requested location beginning at the target address.

MEMORY FUNCTION COMMANDS

The Memory Function Flow Chart (Figure 7) describes the protocols necessary for accessing the memory.
An example follows the flowchart. The communication between master and DS2423 takes place either at
regular speed (default, OD = 0) or at Overdrive speed (OD = 1). If not explicitly set into the Overdrive
mode the DS2423 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 be
ignored and the partial byte flag PF will be set.

When executing the Write Scratchpad command the CRC generator inside the DS2423 (see Figure 12)
calculates a CRC over the entire data stream, starting at the command code and ending at the last data
byte 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 read
time slots and will receive the CRC generated by the DS2423.

The memory address range of the DS2423 is 0000H to 01FFH. If the bus master sends a target address
higher than this, the internal circuitry of the chip will set seven 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 DS2423. 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, a
subsequent Copy Scratchpad command will not work since the most significant bits of the target address
the master sends will not match the value the DS2423 expects.

DS2423

6 of 25

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 the
ending 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 the
scratchpad 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 three
address 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 with
this command. The AA flag will be cleared only by executing a Write Scratchpad command.

DS2423

8 of 25

Read Memory [F0H]

The read memory command may be used to read the entire memory. After issuing the command, the
master must provide the 2-byte target address. After the two bytes, the master reads data beginning from
the target address and may continue until the end of memory, at which point logic 1s will be read. It is
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 DS2423 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 is
recommended 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 that
eliminate having to read a page multiple times to determine if the received data is correct or not. (See the
Book 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 counter
or externally triggered counter associated with the addressed page of data memory. The additional
information is transmitted by the DS2423 as the end of a memory page is encountered. Following the
current value of the counter the DS2423 transmits 32 0-bits and a 16-bit CRC generated by the DS2423.

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 DS2423 starting at the
initial 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 the
addressed 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 the
page, 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 of
shifting the command byte into the cleared CRC generator, followed by the two address bytes, the
contents 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 then
shifting 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 DS2423 until a Reset Pulse is
issued. The Read Memory + Counter command sequence can be ended at any point by issuing a Reset
Pulse.

DS2423

9 of 25

MEMORY FUNCTION FLOW CHART Figure 7

Master TX Memory

Function Command

0FH

Write

Scratchpad

DS2423 sets Scratch-

pad Offset = (T4:T0)

and Clears (PF, AA)

Master TX Data Byte

to Scratchpad Offset

DS2423 sets (E4:E0)

= Scratchpad Offset

Master

TX Reset?

Scratch-

pad Offset =

11111b?

Master RX CRC16 of

Command, Address, Data

DS2423 Incre-

ments Scratch-

pad Offset

Master RX "1"s

Master

TX Reset?

Master

TX Reset?

Partial

Byte Written?

PF = 1

AAH

Read

Scratchpad

Master RX Ending

Offset with Data

Status (E/S)

Master

TX Reset?

Scratch-

pad Offset =

11111b?

DS2423 Incre-

ments Scratch-

pad Offset

Master RX "1"s

DS2423 sets Scratch-

pad Offset = (T4:T0)

Master RX Data Byte

from Scratchpad Offset

From ROM Functions

Flow Chart (Figure 9)

To ROM Functions

Flow Chart (Figure 9)

Master TX

TA1 (T7:T0)

Master TX

TA2 (T15:T8)

Master RX

TA1 (T7:T0)

Master RX

TA2 (T15:T8)

To Figure 7

Part

From Figure 7

Part

1) To be transmitted or received at Overdrive speed if OD = 1.
2) Reset Pulse to be transmitted at Overdrive speed if OD = 1.

Reset Pulse to be transmitted at normal speed if OD = 0 or if
the DS2423 is to be reset from Overdrive speed to regular
speed.

DS2423

10 of 25

MEMORY FUNCTION FLOW CHART Figure 7 cont'd

To Figure 7

Part

55H

Copy

Scratchpad

Master TX

E/S Byte

Authorization

Code Match?

DS2423 Copies Scratchpad

Data to Memory

Copying

Finished

Master

TX Reset?

Master

TX Reset?

AA = 1

F0H

Read

Memory

Master

TX Reset?

End of

Memory?

Master RX "0"s

DS2423 sets Memory

Address = (T15:T0)

Master RX Data Byte

from Memory Address

Master TX

TA2 (T15:T8)

Master

RX "1"s

DS2423 TX "0"

DS2423 TX "1"

Master

TX Reset?

Master

RX "1"s

Master TX

TA1 (T7:T0)

DS2423 Incre-

ments Address

Counter

Master TX

TA1 (T7:T0)

Master TX

TA1 (T7:T0)

From Figure 7

Part

To Figure 7

Part

From Figure 7

Part

1) To be transmitted or received at Overdrive speed if OD = 1.
2) Reset Pulse to be transmitted at Overdrive speed if OD = 1.

Reset Pulse to be transmitted at normal speed if OD = 0 or if
the DS2423 is to be reset from Overdrive speed to regular
speed.

DS2423

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MEMORY FUNCTION FLOW CHART Figure 7 cont'd

DS2423 Sets Memory

Address = (T15:T0)

DS2423 Increments

Address Counter

End of
Page?

End of

Memory?

CRC

Correct?

Master RX Data

From Memory

Master

TX Reset?

Master TX

TA2 (T15:T8)

Master RX "1"s

Master RX Counter

Value of Memory Page

Master RX 32 Zero Bits

Master

TX Reset?

Master RX CRC 16 of Command, Address,

Data, Counter, Zero Bits (1

Pass)

CRC 16 of Data, Counter, Zero Bits

(Subsequent Passes)

A5H

Read Memory

+ Counter

Master TX

TA1 (T7:T0)

From Figure 7

Part

To Figure 7

Part

Master

TX Reset?

Master TX

Reset

1) To be transmitted or received at Overdrive speed if OD = 1.
2) Reset Pulse to be transmitted at Overdrive speed if OD = 1.

Reset Pulse to be transmitted at normal speed if OD = 0 or if
the DS2423 is to be reset from Overdrive speed to regular
speed.

DS2423

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MEMORY FUNCTION EXAMPLE

Example: Write two data bytes to memory location 0026 and 0027. Read entire memory.

MASTER MODE

DATA (LSB FIRST)

COMMENTS

Reset

Reset pulse (480-960 µs)

Presence

Presence pulse

CCh

Issue "skip ROM" command

0Fh

Issue "write scratchpad" command

26h

TA1, beginning offset=26h

00h

TA2, address=0026h

<2 data bytes>

Write 2 bytes of data to scratchpad

Reset

Reset pulse

Presence

Presence pulse

CCh

Issue "skip ROM" command

AAh

Issue "read scratchpad" command

26h

Read TA1, beginning offset=26h

00h

Read TA2, address=0026h

07h

Read E/S, ending offset=7h, flags=0h

<2 data bytes>

Read scratchpad data and verify

Reset

Reset pulse

Presence

Presence pulse

CCh

Issue "skip ROM" command

5Ah

Issue "copy scratchpad" command

26h

00h

07h

TA1
TA2

AUTHORIZATION CODE

E/S

Reset

Reset pulse

Presence

Presence pulse

CCh

Issue "skip ROM" command

F0h

Issue "read memory" command

00h

TA1, beginning offset=0

00h

TA2, address=0000h

<512 bytes>

Read entire memory

Reset

Reset pulse

Presence

Presence pulse, done

DS2423

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MEMORY FUNCTION EXAMPLE

Read page 14 and counts of Input A. Rewrite page 14 with 32 bytes. Read Memory + Counter, Write
Scratchpad, Copy Scratchpad.

MASTER MODE

DATA (LSB FIRST)

COMMENTS

Reset

Reset pulse (480-960 µs)

Presence

Presence pulse

CCh

Issue "skip ROM" command

A5h

Issue "read memory + counter" command

C0h

TA1, beginning offset=C0h

01h

TA2, address=01C0h

<32 data bytes>

Read 32 bytes of data

<4 data bytes>

Read Counts of Input A

<4 data bytes>

Read 32 Zero Bits

<2 data bytes>

Read (inverted) CRC16

Reset

Reset pulse

Presence

Presence pulse

CCh

Issue "skip ROM" command

0Fh

Issue "write scratchpad" command

C0h

TA1, beginning offset=C0h

01h

TA2, address=01C0h

<32 data bytes>

Read 32 bytes of data to scratchpad

<2 data bytes>

Read (inverted) CRC16

Reset

Reset pulse

Presence

Presence pulse

CCh

Issue "skip ROM" command

5Ah

Issue "copy scratchpad" command

C0h

01h

1Fh

TA1
TA2

AUTHORIZATION CODE

E/S

<1 data byte>

Read Copy Scratchpad response

Reset

Reset pulse

Presence

Presence pulse, done

DS2423

14 of 25

HARDWARE CONFIGURATION Figure 8

Note: Depending on the 1-Wire communication speed and the bus load characteristics, the optimal pull-
up resistor (R

) value will be in the 1.5k

W 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 the
DS2423 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-Wire
signaling (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 to
drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open-
drain or 3-state outputs. The 1-Wire port of the DS2423 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 5k. The 1-Wire bus requires a pullup resistor range of 1.5k

W to 5kW, depending on the

bus 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 DS2423 via the 1-Wire port is as follows:

§ Initialization
§ ROM Function Command
§ Memory Function Command
§ Transaction/Data

DS2423

DS2423

15 of 25

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 the
slave(s).

The Presence Pulse lets the bus master know that the DS2423 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 DS2423'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 DS2423 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (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 DS2423 on a multidrop bus. Only the DS2423 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 the
bus.

Skip ROM [CCH]

This command can save time in a single-drop bus system by allowing the bus master to access the
memory 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 as
multiple 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 1-
Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process
of 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 the
desired 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 the
Book 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 DS2423 in the Overdrive mode (OD = 1). All communication following this
command 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).

DS2423

16 of 25

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 the
time for the search process. If more than one slave supporting Overdrive is present on the bus and the
Overdrive Skip ROM command is followed by a read command, data collision will occur on the bus as
multiple 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 DS2423 on a multidrop bus and to simultaneously set it
in Overdrive mode. Only the DS2423 that exactly matches the 64-bit ROM sequence will respond to the
subsequent 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 or
multiple devices on the bus.

DS2423

17 of 25

ROM FUNCTIONS FLOW CHART Figure 9 (First Part)

To Memory Functions

Flow Chart (Figure 7)

DS2423 TX Bit 63

Master TX Bit 63

DS2423 TX Bit 63

DS2423 TX Bit 1

Master TX Bit 1

DS2423 TX Bit 1

DS2423 TX Bit 0

Master TX Bit 0

DS2423 TX Bit 0

Bit 63 Match?

Bit 1 Match?

Bit 0 Match?

F0H

ROM?

Master TX Bit 63

Master TX Bit 1

Master TX Bit 0

Bit 63 Match?

Bit 1 Match?

Bit 0 Match?

55H

Match

ROM?

DS2423 TX

CRC Byte

DS2423 TX

Serial Number

6 Bytes

DS2423 TX

Family Code

1 Byte

33H

Read

ROM?

From Memory Functions

Flow Chart (Figure 7)

Master TX ROM

Function Command

DS2423 TX

Presence Pulse

Master TX

Reset Pulse

Short

Reset Pulse?

OD = 0

1)
1)
1)

1) To be transmitted or received at Overdrive speed if

OD = 1.

2) The Presence Pulse will be short if OD = 1.

From Figure 9

Part

From Figure 9

Part

To Figure 9

Part

To Figure 9

Part

DS2423

19 of 25

1-WIRE SIGNALING

The DS2423 requires strict protocols to ensure data integrity. The protocol consists of four types of
signaling 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 DS2423 can communicate at
two different speeds, regular speed and Overdrive speed. If not explicitly set into the Overdrive mode, the
DS2423 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 DS2423 is shown in Figure 10.
A Reset Pulse followed by a Presence Pulse indicates the DS2423 is ready to send or receive data given
the correct ROM command and memory function command. The bus master transmits (TX) a Reset
Pulse (t

RSTL

, 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 DS2423 waits (t

PDH

, 15-60µs at regular speed, 2-6µs at

Overdrive speed) and then transmits the Presence Pulse (t

PDL

, 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 DS2423 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 the
master driving the data line low. The falling edge of the data line synchronizes the DS2423 to the master
by triggering a delay circuit in the DS2423. During write time slots, the delay circuit determines when the
DS2423 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 DS2423 will hold the data line low overriding the 1 generated by the master. 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

DS2423

DS2423

21 of 25

Read-Data Time Slot

RESISTOR

MASTER

DS2423

REC

PUP

PUPMIN

IHMIN

ILMAX

Master

Sampling

Window

LOWR

SLOT

RDV

RELEASE

CRC GENERATION

With the DS2423 there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is an 8-
bit 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 DS2423 to
determine if the ROM data has been received error-free by the bus master. The equivalent polynomial
function of this CRC is: X

+ X

+ 1. This 8-bit CRC is received in the true (non-inverted) form

when reading the ROM of the DS2423. 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 x

+ x

+ 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 the
same 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 the
complemented (inverted) form. A CRC-generator inside the DS2423 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 an
operation or re-read the portion of the data with the CRC error.

With the Write Scratchpad command the CRC is generated by first clearing the CRC generator and then
shifting in the command code, the Target Addresses TA1 and TA2 and all the data bytes. The DS2423
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 and
software, see the Book of DS19xx iButton Standards.

DS2423

23 of 25

ABSOLUTE MAXIMUM RATINGS*

Voltage on Any Pin Relative to Ground

-0.5V to +7.0V

Operating Temperature Range

-40°C to +85°C

Storage Temperature Range

-55°C to +125°C

Soldering Temperature

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 (V

PUP

= 2.8V to 6.0V; V

BAT

= 2.8 to 5.5V;-40°C to +85°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Logic 1

2.2

1, 8

Logic 0

-0.3

+0.8

1, 9

Output Logic Low @ 4 mA

0.4

Output Logic High

PUP

6.0

1, 2

Input Load Current

µA

Standby Current

BATS

200

I/O Operate Charge

BATO

200

12, 16

CAPACITANCE

= 25°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

I/O (1-Wire)

IN/OUT

100

800

6, 16

COUNTER INPUT CHARACTERISTICS

PUP

= 2.8V to 6.0V; V

BAT

= 2.8 to 5.5V;-40°C to +85°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Trip Point

TRIP

BAT

Logic 1

INH

TRIP

BAT

+0.3

1, 10

Logic 0

INL

-0.3

TRIP

Internal Pullup Resistor

11, 16

Debounce Time

DEB

170

290

460

µs

Pulse Width (Active Low)

µs

DS2423

24 of 25

AC CHARACTERISTICS REGULAR SPEED

PUP

= 2.8V to 6.0V; V

BAT

= 2.8 to 5.5V;-40°C to +85°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Time Slot

SLOT

120

µs

Write 1 Low Time

LOW1

µs

Write 0 Low Time

LOW0

120

µs

Read Low Time

LOWR

µs

Read Data Valid

RDV

µs

14, 16

Release Time

RELEASE

µs

Read Data Setup

µs

Recovery Time

REC

µs

Reset Time High

RSTH

480

µs

Reset Time Low

RSTL

480

960

µs

Presence Detect High

PDH

µs

Presence Detect Low

PDL

240

µs

AC CHARACTERISTICS OVERDRIVE SPEED

PUP

= 2.8V to 6.0V; V

BAT

= 2.8 to 5.5V;-40°C to +85°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Time Slot

SLOT

µs

Write 1 Low Time

LOW1

µs

Write 0 Low Time

LOW0

µs

Read Low Time

LOWR

µs

Read Data Valid

RDV

µs

14, 16

Release Time

RELEASE

1.5

µs

Read Data Setup

µs

Recovery Time

REC

µs

Reset Time High

RSTH

µs

Reset Time Low

RSTL

µs

Presence Detect High

PDH

µs

Presence Detect Low

PDL

µs

DS2423

25 of 25

NOTES:

1) All voltages are referenced to ground.

2) V

PUP

= 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 is

guaranteed 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 5k resistor is used to

pull up the data line to V

PUP

, 5µs after power has been applied the parasite capacitance will not affect

normal communications.

7) The reset low time (t

RSTL

) should be restricted to a maximum of 960µs, to allow interrupt signaling,

otherwise, it could mask or conceal interrupt pulses.

8) V

is a function of the external pullup resistor and V

PUP

9) Under certain low voltage conditions V

ILMAX

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 V

BAT

12) Read and write scratchpad (all 32 bytes) at V

BAT

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 the
debounce time must have expired.

14) The optimal sampling point for the master is as close as possible to the end time of the t

RDV

period

without exceeding t

RDV

. For the case of a Read-One Time slot, this maximizes the amount of time for

the 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 1-
Wire device samples in the case of a Write-One Time or before the master samples in the case of a
Read-One Time.

16) Guaranteed by design; not production tested.

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ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: DS2423