Avago Technologies LSI8751D User Manual

Page 192

5-76

SCSI Operating Registers

HSC

Halt SCSI Clock

Asserting this bit causes the internal divided SCSI clock
to come to a stop in a glitchless manner. This bit is used
for test purposes or to lower I

during a power-down

mode.

This bit is used when the SCSI clock doubler is operating.
For additional information on the clock doubler, see

Chapter 2, “Functional Description.”

DSI

Disable Single Initiator Response

If this bit is set, the LSI53C875 ignores all bus-initiated
selection attempts that employ the single initiator option
from SCSI-1. In order to select the LSI53C875 while this
bit is set, the LSI53C875’s SCSI ID and the initiator’s
SCSI ID must both be asserted. Assert this bit in
SCSI-2 systems so that a single bit error on the SCSI bus
is not interpreted as a single initiator response.

S16

16-Bit System

If this bit is set, all devices in the SCSI system
implementation are assumed to be 16-bit. This causes
the LSI53C875 to always check the parity bit for SCSI
IDs [15:8] during bus-initiated selection or reselection,
assuming parity checking has been enabled. If an 8-bit
SCSI device attempts to select the LSI53C875 while this
bit is set, the LSI53C875 will ignore the selection attempt.
This is because the parity bit for IDs [15:8] will be
undriven. See the description of the Enable Parity
Checking bit in the

SCSI Control Zero (SCNTL0)

for more information.

TTM

Timer Test Mode

Asserting this bit facilitates testing of the selection
time-out, general purpose, and handshake-to-handshake
timers by greatly reducing all three time-out periods.
Setting this bit starts all three timers and if the respective
bits in the

SCSI Interrupt Enable One (SIEN1)

are asserted, the LSI53C875 generates interrupts at
time-out. This bit is intended for internal manufacturing
diagnosis and should not be used.

CSF

Clear SCSI FIFO

Setting this bit causes the “full flags” for the SCSI FIFO
to be cleared. This empties the FIFO. This bit is
self-clearing. In addition to the SCSI FIFO pointers, the

This manual is related to the following products:

LSI53C875E