3

Analog Devices

shift register bits are initialized to zero. 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 is

entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC

value. Shifting in the eight bits of CRC should return the shift register to all zeros. The 64-bit ROM and

ROM Function Control sections allow the DS1904 to operate as a 1-Wire device and follow the 1-Wire

protocol detailed in Chapter 5 of the Book of iButton® Standards.

Hierarchical Structure for 1-Wire Protocol Figure 2

64-Bit Lasered ROM Figure 3

1-Wire CRC Generator Figure 4

8-BIT CRC CODE

48-BIT SERIAL NUMBER

8-BIT FAMILY CODE [01h]

MSB

LSB

MSB

LSB MSB

LSB MSB

LSB

BUS

CONTROLLER

OTHER

DEVICES

1-Wire BUS

COMMAND

LEVEL:

DS1904

AVAILABLE

COMMANDS:

DATA FIELD

AFFECTED:

READ ROM

MATCH ROM

SEARCH ROM

SKIP ROM

1-Wire ROM FUNCTION

COMMANDS (SEE FIGURE 7)

DS1904-SPECIFIC

FUNCTION

COMMANDS (SEE FIGURE 5)

WRITE CLOCK

READ CLOCK

64-BIT ROM

64-BIT ROM

64-BIT ROM

N/A

RTC COUNTER, DEVICE CONTROL

RTC COUNTER, DEVICE CONTROL

X0

INPUT DATA

1st

STAGE

2nd

STAGE

3rd

STAGE

4th

STAGE

5th

STAGE

6th

STAGE

7th

STAGE

8th

STAGE

X1

X2

X3

X4

X5

X6

X7

X8

POLYNOMIAL = X8 + X5 + X4 + 1