LSI LSI53C895A, Technical Manual

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SCSI Registers 4-93
Note: Never set this bit during fast SCSI (greater than 5 Mbyte
transfers per second) operations, because a valid assertion
could be treated as a glitch.
LOW SCSI Low level Mode 0
Setting this bit places the LSI53C895A in the low level
mode. In this mode, no DMA operations occur, and no
SCRIPTS execute. Arbitration and selection may be
performed by setting the start sequence bit as described
in the
SCSI Control Zero (SCNTL0) register. SCSI bus
transfers are performed by manually asserting and polling
SCSI signals. Clearing this bit allows instructions to be
executed in SCSI SCRIPTS mode.
Note: It is not necessary to set this bit for access to the SCSI
bit-level registers
SCSI Output Data Latch (SODL) , SCSI
Bus Control Lines (SBCL) , and input registers.
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 LSI53C895A is driving these
signals. Active deassertion of these signals occurs only
when the LSI53C895A 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.
7 6 5 4 3 2 1 0
TE STR HSC DSI S16 TTM CSF STW
0 0 0 0 x 0 0 0