DS2406

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PROGRAM PULSE TIMING DIAGRAM Figure 16

Resistor pull-up

LINE TYPE LEGEND:

Bus master active high

(12 V @ 10 mA)

V

PULLUP

V

PP

GND

480 µs

t

RP

t

FP

t

DP

t

DV

> 5 µs

> 5 µs

t

PP

Normal 1-Wire

Communication Ends

Normal 1-Wire

Communication Resumes

CRC GENERATION

With the DS2406 there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is an 8-

bit type. It is computed at the factory and lasered into the most significant byte of the 64-bit ROM. The

equivalent polynomial function of this CRC is X

8

+ X

5

+ X

4

+ 1. To determine whether the ROM data has

been read without error the bus master can compute the CRC value from the first 56 bits of the 64-bit

ROM and compare it to the value read from the DS2406. This 8-bit CRC is received in the true form

(non-inverted) when reading the ROM.

The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function X

16

+ X

15

+ X

2

+ 1. This CRC is used for error detection when reading Data Memory, Status Memory or

when communicating with PIO channels. It is the same type of CRC as is used with NVRAM 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 in the complemented (inverted) form. A CRC-generator inside the DS2406

chip (Figure 17) will calculate a new 16-bit CRC as shown in the command flow chart of Figure 7. The

bus master may compare the CRC value read from the device to the one it calculates from the data and

decides whether to continue with an operation or to re-do the function that returned the CRC error.

When reading the data memory of the DS2406 with the Read Memory command, the 16-bit CRC is only

transmitted at the end of the memory. This CRC is generated by clearing the CRC generator, shifting in

the command, low address, high address and every data byte starting at the first addressed memory

location and continuing until the end of the physical data memory is reached.

When reading the Status Memory, the 16-bit CRC is transmitted at the end of the 8-byte Status Memory

page. The 16-bit CRC will be generated by clearing the CRC generator, shifting in the command byte,

low address, high address and the data bytes beginning at the first addressed memory location and

continuing until the last byte of the Status Memory is reached.

When reading the data memory of the DS2406 with the Extended Read Memory command, there are two

situations where a 16-bit CRC is generated. One 16-bit CRC follows each Redirection Byte; another 16-

bit CRC is transmitted after the last byte of a memory data page is read. The CRC at the end of the

memory page is always the result of clearing the CRC generator and shifting in the data bytes beginning

at the first addressed memory location of the EPROM data page until the last byte of this page. With the