LSI 53C875A - Manual (Page 115)

SCSI Registers 4-23
( SET TARGET or CLEAR TARGET ). When this bit is set, the
chip is a target device by default. When this bit is cleared,
the LSI53C875A is an initiator device by default.
Caution: Writing this bit while not connected may cause the loss of
a selection or reselection due to the changing of target or
initiator modes.
Register: 0x01
SCSI Control One (SCNTL1)
Read/Write
EXC Extra Clock Cycle of Data Setup 7
When this bit is set, an extra clock period of data setup
is added to each SCSI data transfer. The extra data setup
time can provide additional system design margin, though
it affects the SCSI transfer rates. Clearing this bit disables
the extra clock cycle of data setup time. Setting this bit
only affects SCSI send operations.
ADB Assert SCSI Data Bus 6
When this bit is set, the LSI53C875A drives the contents
of the
SCSI Output Data Latch (SODL) register onto the
SCSI data bus. When the LSI53C875A is an initiator, the
SCSI I/O signal must be inactive to assert the SODL
contents onto the SCSI bus. When the LSI53C875A is a
target, the SCSI I/O signal must be active to assert the
SODL contents onto the SCSI bus. The contents of the
SCSI Output Data Latch (SODL) register can be asserted
at any time, even before the LSI53C875A is connected to
the SCSI bus. Clear this bit when executing SCSI
SCRIPTS. It is normally used only for diagnostic testing
or operation in low level mode.
DHP Disable Halt on Parity Error or ATN (Target Only) 5
The DHP bit is only defined for target mode. When this
bit is cleared, the LSI53C875A halts the SCSI data
transfer when a parity error is detected or when the
SATN/ signal is asserted. If SATN/ or a parity error is
received in the middle of a data transfer, the LSI53C875A
7 6 5 4 3 2 1 0
EXC ADB DHP CON RST AESP IARB SST
0 0 0 0 0 0 0 0