Avago Technologies LSI53C876E - Manual (Page 174)

4-80 Registers
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 SCSI Longitudinal Parity (SLPAR) register also
generates the check bytes for SCSI send operations. If
the 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 resets 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)
Even parity >>> 10010110
4. 10010110 00000000