B.2. LFSR Checksum Functions

The checksum algorithm uses the same LFSR as is used in the initiation key process.

Figure B-2. Checksum LFSR

The LFSR resets to 0x6A upon receiving the Wake[CSN] command. The next shift value for the LFSR is calculated as LFSR[1] XOR LFSR[0] XOR Serial Data. The LFSR is shifted right one bit at the conclusion of each pair of reads to the Serial Isolation register. LFSR[7] is assigned the next shift value described above.

As an example of the data pattern generated by the LFSR during the serial shift protocol consider a card with a vendor abbreviation of "PXQ", a manufacturer-specific product number of 540, a revision level of "9", and a serial number of 0x04000100.

The ASCII EISA ID for "PXQ" is 0x1143 where 0x43 is byte 0 and 0x11 is byte 1 as per Table 2, Section 6.1.

Vendor ID Byte 0:	0x43
Vendor ID Byte 1:	0x11
Vendor ID Byte 2:	0x54
Vendor ID Byte 3:	0x09
Serial Number Byte 0:	0x00
Serial Number Byte 1:	0x01
Serial Number Byte 2:	0x00
Serial Number Byte 3:	0x04

The serial identifier is sent as

0x43 (Bit 0 to bit 7, 1 1 0 0 0 0 1 0)
0x11                  1 0 0 0 1 0 0 0
0x54                  0 0 1 0 1 0 1 0
0x09                  1 0 0 1 0 0 0 0
0x00                  0 0 0 0 0 0 0 0
0x01                  1 0 0 0 0 0 0 0
0x00                  0 0 0 0 0 0 0 0
0x04                  0 0 1 0 0 0 0 0

The LFSR is reset to value 0x6A when this card receives a Wake[CSN] command. After 64 pairs of reads of the Serial Isolation register, the LFSR will have the value 0xDC.