LSI 53C875A - Manual (Page 183)

SCSI Registers 4-91
Register: 0x4F
SCSI Test Three (STEST3)
Read/Write
TE TolerANT Enable 7
Setting this bit enables the active negation portion of
LSI Logic TolerANT technology. Active negation causes
the SCSI Request, Acknowledge, Data, and Parity
signals to be actively deasserted, instead of relying on
external pull-ups, when the LSI53C875A is driving these
signals. Active deassertion of these signals occurs only
when the LSI53C875A is in an information transfer
phase. When operating in a differential environment or at
fast SCSI timings, TolerANT Active negation should be
enabled to improve setup and deassertion times. Active
negation is disabled after reset or when this bit is cleared.
For more information on LSI Logic TolerANT technology,
see
Chapter 1, “General Description.”
Note: Set this bit if the Enable Ultra SCSI bit in SCSI Control
Three (SCNTL3) is set.
STR SCSI FIFO Test Read 6
Setting this bit places the SCSI core into a test mode in
which the SCSI FIFO is easily read. Reading the least
significant byte of the
SCSI Output Data Latch (SODL)
register causes the FIFO to unload. The functions are
summarized in the table below.
HSC Halt SCSI Clock 5
Asserting this bit causes the internal divided SCSI clock
to come to a stop in a glitchless manner. This bit is used
7 6 5 4 3 2 1 0
TE STR HSC DSI S16 TTM CSF STW
0 0 0 0 x 0 0 0
Register
Name
Register
Operation FIFO Bits
FIFO
Function
SODL Read [15:0] Unload
SODL0 Read [7:0] Unload
SODL1 Read [15:8] None