LSI53C875 LSI Logic, LSI53C875 Datasheet - Page 192

• Manufacturer Part Number: LSI53C875
• Description: PCI to Ultra SCSI I/O Processor
• Manufacturer: LSI Logic

5-76
HSC
DSI
S16
TTM
CSF
SCSI Operating Registers
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
mode.
This bit is used when the SCSI clock doubler is operating.
For additional information on the clock doubler, see
Chapter 2, “Functional Description.”
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.
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
for more information.
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
are asserted, the LSI53C875 generates interrupts at
time-out. This bit is intended for internal manufacturing
diagnosis and should not be used.
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
SCSI Interrupt Enable One (SIEN1)
SCSI Control Zero (SCNTL0)
DD
during a power-down
register
register
5
4
3
2
1