Avago Technologies LSI53C895A - Manual (Page 189)

SCSI Registers 4-81
HTH Handshake-to-Handshake Timer Expired 0
This bit is set when the handshake-to-handshake timer
expires. The time measured is the SCSI Request to
Request (target) or Acknowledge-to-Acknowledge
(initiator) period. See the description of the
SCSI Timer
Zero (STIME0) register, bits [7:4], for more information on
the handshake-to-handshake timer.
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 is also used to generate the check
bytes for SCSI send operations. If the SLPAR register
contains all zeros prior to sending a block move, it
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
4. 10010110 00000000