1024-Bit EEPROM iButton

20

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by the bus master. The DS1972 transmits this CRC only

if E[2:0] = 111b.

With the Read Scratchpad command, the CRC is gen-

erated by first clearing the CRC generator and then

shifting in the command code, the target addresses

TA1 and TA2, the E/S byte, and the scratchpad data as

they were sent by the DS1972. The DS1972 transmits

this CRC only if the reading continues through the end

of the scratchpad. For more information on generating

CRC values, refer to Application Note 27.

1ST

STAGE

2ND

STAGE

3RD

STAGE

4TH

STAGE

7TH

STAGE

8TH

STAGE

6TH

STAGE

5TH

STAGE

X0

X1

X2

X3

X4

POLYNOMIAL = X16 + X15 + X2 + 1

INPUT DATA

CRC OUTPUT

X5

X6

11TH

STAGE

12TH

STAGE

15TH

STAGE

14TH

STAGE

13TH

STAGE

X11

X12

9TH

STAGE

10TH

STAGE

X9

X10

X13

X14

X7

16TH

STAGE

X16

X15

X8

Figure 13. CRC-16 Hardware Description and Polynomial

Command-Specific 1-Wire Communication Protocol—Legend

SYMBOL

DESCRIPTION

RST

1-Wire reset pulse generated by master.

PD

1-Wire presence pulse generated by slave.

Select

Command and data to satisfy the ROM function protocol.

WS

Command “Write Scratchpad.”

RS

Command “Read Scratchpad.”

CPS

Command “Copy Scratchpad.”

RM

Command “Read Memory.”

TA

Target address TA1, TA2.

TA-E/S

Target address TA1, TA2 with E/S byte.

<8–T[2:0] bytes>

Transfer of as many bytes as needed to reach the end of the scratchpad for a given target address.

<Data to EOM>

Transfer of as many data bytes as are needed to reach the end of the memory.

CRC-16

Transfer of an inverted CRC-16.

FF Loop

Indefinite loop where the master reads FF bytes.

AA Loop

Indefinite loop where the master reads AA bytes.

Programming

Data transfer to EEPROM; no activity on the 1-Wire bus permitted during this time.