LSI 53C875A Disable Single Initiator Response, S16 Bit System, Ttm, Timer Test Mode

for test purposes or to lower IDD during a power-down mode.

DSI	Disable Single Initiator Response	4
	If this bit is set, the LSI53C875A ignores all bus-initiated
	selection attempts that employ the single initiator option
	from SCSI-1. In order to select the LSI53C875A while this
	bit is set, the LSI53C875A’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	3
	If this bit is set, all devices in the SCSI system
	implementation are assumed to be 16-bit. This causes
	the LSI53C875A 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 LSI53C875A while
	this bit is set, the LSI53C875A will ignore the selection
	attempt. This is because the parity bit for IDs [15:8] will
	not be driven. See the description of the Enable Parity
	Checking bit in the SCSI Control Zero (SCNTL0) register
	for more information.

TTM	Timer Test Mode	2
	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) register
	are asserted, the LSI53C875A generates interrupts at
	time-out. This bit is intended for internal manufacturing
	diagnosis and should not be used.

CSFClear SCSI FIFO1

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 Input Data Latch (SIDL), SCSI Output Data Latch (SODL), and (SODR, a hidden buffer register which is not accessible) full bits in the SCSI Status Zero (SSTAT0) and SCSI Status Two (SSTAT2) are cleared.

4-92Registers