LSI 53C875A - Manual (Page 177)

SCSI Registers 4-85
Register: 0x49
SCSI Timer One (STIME1)
Read/Write
R Reserved 7
HTHBA Handshake-to-Handshake Timer Bus Activity
Enable
6
Setting this bit causes this timer to begin testing for SCSI
REQ/, ACK/ activity as soon as SBSY/ is asserted,
regardless of the agents participating in the transfer.
GENSF General Purpose Timer Scale Factor 5
Setting this bit causes this timer to shift by a factor of 16.
Refer to the
SCSI Timer Zero (STIME0) register
description for details.
HTHSF Handshake-to-Handshake Timer Scale Factor 4
Setting this bit causes this timer to shift by a factor of 16.
Refer to the
SCSI Timer Zero (STIME0) register
description for details.
GEN[3:0] General Purpose Timer Period [3:0]
These bits select the period of the general purpose timer.
The time measured is the time between enabling and
disabling of the timer. When this timing is exceeded, the
GEN bit in the
SCSI Interrupt Status One (SIST1) register
is set. Refer to the table under SCSI Timer Zero
(STIME0) , bits [3:0], for the available time-out periods.
Note: To reset a timer before it expires and obtain repeatable
delays, the time value must be written to zero first, and then
written back to the desired value. This is also required
when changing from one time value to another.
7 6 5 4 3 0
R HTHBA GENSF HTHSF GEN[3:0]
x 0 0 0 0 0 0 0