Avago Technologies LSI53C896 - Manual (Page 195)

SCSI Registers 4-83
Version 3.3 Copyright © 1998–2003 by LSI Logic Corporation. All rights reserved.
Register: 0x44
SCSI Longitudinal Parity (SLPAR)
Read/Write
SLPAR SCSI Longitudinal Parity [7:0]
This register performs a bytewise longitudinal parity
check on all SCSI data received or sent through the SCSI
core. If one of the bytes received or sent (usually the last)
is the set of correct even parity bits, SLPAR should go to
zero (assuming it started at zero). As an example,
suppose that the following three data bytes and one
check byte are received from the SCSI bus (all signals
are shown active HIGH):
A one in any bit position of the final SLPAR value would
indicate a transmission error.
The SLPAR register also generates the check bytes for
SCSI send operations. If the
SCSI Longitudinal Parity (SLPAR) register contains all
zeros prior to sending a block move, it contains the
appropriate check byte at the end of the block move. This
byte must then be sent across the SCSI bus.
Note: Writing any value to this register clears it to zero.
7 0
SLPAR
x x x x x x x x
Data Bytes Running SLPAR
– 00000000
1. 11001100 11001100 (XOR of word 1)
2. 01010101 10011001 (XOR of word 1 and 2)
3. 00001111 10010110 (XOR of word 1, 2 and 3)
4. 10010110 00000000