Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsIntegrated Circuits (ICs)TSOC 6 1 kBit 256 x 4

The hierarchical structure of the 1-Wire protocol is shown

in Figure 2. The bus master must first provide one of

the seven ROM function commands: Read ROM, Match

ROM, Search ROM, Skip ROM, Resume, Overdrive-Skip

ROM, or Overdrive-Match ROM. Upon completion of an

Overdrive-Skip ROM or Overdrive-Match ROM command

byte executed at standard speed, the device enters over-

drive 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 can provide

any one of the four memory function commands. The pro-

tocol for these memory function commands is described

in Figure 7. All data is read and written least signifi-

cant bit first.

64-Bit Lasered ROM

Each DS2431 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 cyclic

redundancy check (CRC) of the first 56 bits. See Figure 3

for details. The 1-Wire CRC is generated using a polyno-

mial generator consisting of a shift register and XOR gates

as shown in Figure 4. The polynomial is X

+ X

+ 1.

Additional information about the 1-Wire CRC is available

in Application Note 27: Understanding and Using Cyclic

Redundancy Checks with Maxim iButton® Products.

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, the serial number is entered. After the last

bit of the serial number has been entered, the shift reg-

ister contains the CRC value. Shifting in the 8 bits of the

CRC returns the shift register to all 0s.

Figure 2. Hierarchical Structure for 1-Wire Protocol

Figure 3. 64-Bit Lasered ROM

iButton is a registered trademark of Maxim Integrated Products, Inc.

DS2431 COMMAND LEVEL:

AVAILABLE COMMANDS: DATA FIELD AFFECTED:

READ ROM

MATCH ROM

SEARCH ROM

SKIP ROM

RESUME

OVERDRIVE-SKIP ROM

OVERDRIVE-MATCH ROM

64-BIT REG. #, RC-FLAG

RC-FLAG

RC-FLAG, OD-FLAG

64-BIT REG. #, RC-FLAG, OD-FLAG

1-Wire ROM FUNCTION COMMANDS

(SEE FIGURE 9)

WRITE SCRATCHPAD

READ SCRATCHPAD

COPY SCRATCHPAD

READ MEMORY

64-BIT SCRATCHPAD, FLAGS

64-BIT SCRATCHPAD

DATA MEMORY, REGISTER PAGE

DS2431-SPECIFIC

MEMORY FUNCTION COMMANDS

(SEE FIGURE 7)

MSB

8-BIT

CRC CODE

48-BIT SERIAL NUMBER

MSB MSBLSB

LSB

8-BIT FAMILY CODE

(2Dh)

MSBLSB

DS2431 1024-Bit, 1-Wire EEPROM

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