DS2432X Dallas Semiconducotr, DS2432X Datasheet - Page 28

• Manufacturer Part Number: DS2432X
• Description: 1k-Bit Protected 1-Wire EEPROM with SHA-1 Engine
• Manufacturer: Dallas Semiconducotr

PRELIMINARY
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
X
X
0
8
STAGE
STAGE
9
1
st
th
X
X
9
1
STAGE
STAGE
10
2
nd
th
X
10
STAGE
11
th
X
11
STAGE
X
12
2
STAGE
th
3
Polynomial = X
rd
X
12
STAGE
X
13
3
STAGE
th
4
th
X
13
28 of 30
STAGE
X
14
16
4
STAGE
+ X
th
5
th
X
15
14
+ X
STAGE
X
15
5
STAGE
2
th
+ 1
6
th
INPUT DATA
X
6
STAGE
7
th
X
X
15
7
STAGE
STAGE
16
8
th
th
X
16
CRC
OUTPUT
DS2432