Rainbow Electronics DS2432 - Manual (Page 28)

PRELIMINARY DS2432
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With the Read 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, the E/S byte, and the scratchpad data,
which may have been modified by the DS2432 (see Write Scratchpad command). The DS2432 will
transmit this CRC only if the reading continues through the end of the scratchpad.
With the Read Authenticated Page command 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 data bytes, and the FFh byte.
The CRC that follows the Message Authentication Code (MAC) results from clearing the CRC generator
and then shifting in the 160-bit MAC in the same bit sequence as the master receives it.
For more details on generating CRC values including example implementations in both hardware and
software, see the “Book of DS19xx iButton Standards”.
CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL Figure 12
Polynomial = X
16
+ X
15
+ X
2
+ 1
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
X
8
X
9
X
10
X
11
X
12
X
13
X
14
X
15
X
16
1
st
STAGE
2
nd
STAGE
3
rd
STAGE
4
th
STAGE
6
th
STAGE
5
th
STAGE
7
th
STAGE
8
th
STAGE
9 th
STAGE
10 th
STAGE
11 th
STAGE
12 th
STAGE
13 th
STAGE
14 th
STAGE
15 th
STAGE
16 th
STAGE
INPUT DATA
CRC
OUTPUT