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SCSI Operating Registers
SYM53C875/875E Data Manual
5-49
Register 4A (CA)
Response ID Zero (RESPID0)
Read/Write
Register 4B (CB)
Response ID One(RESPID1)
Read/Write
RESPID0 and RESPID1 contain the selection or
reselection IDs. In other words, these two 8-bit reg-
isters contain the ID that the chip responds to on
the SCSI bus. Each bit represents one possible ID
with the most significant bit of RESPID1 repre-
senting ID 15 and the least significant bit of
RESPID0 representing ID 0. T he SCID register
still contains the chip ID used during arbitration.
T he chip can respond to more than one ID because
more than one bit can be set in the RESPID1 and
RESPID0 registers. However, the chip can arbi-
trate with only one ID value in the SCID register.
Register 4C (CC)
SCSI Test Zero (ST EST 0)
Read Only
Bits 7-4 SSAID (SCSI Selected As ID)
T hese bits contain the encoded value of the
SCSI ID that the SYM53C875 was selected or
reselected as during a SCSI selection or rese-
lection phase. T hese bits are read only and
contain the encoded value of 0-15 possible IDs
that could be used to select the SYM53C875.
During a SCSI selection or reselection phase
when a valid ID has been put on the bus, and
the SYM53C875 responds to that ID, the
“selected as” ID is written into these bits.
T hese bits are used with the RESPID registers
to allow response to multiple IDs on the bus.
Bit 3
SLT (Selection Response Logic Test)
T his bit is set when the SYM53C875 is ready
to be selected or reselected. T his does not take
into account the bus settle delay of 400 ns.
T his bit is used for functional test and fault
purposes.
Bit 2
ART (Arbitration Priority E ncoder
Test)
T his bit will always be set when the
SYM53C875 exhibits the highest priority ID
asserted on the SCSI bus during arbitration. It
is primarily used for chip level testing, but it
may be used during low level mode operation
to determine if the SYM53C875 has won arbi-
tration.
Bit 1
SOZ (SCSI Synchronous Offset
Zero)
T his bit indicates that the current synchronous
SREQ/SACK offset is zero. T his bit is not
latched and may change at any time. It is used
in low level synchronous SCSI operations.
SSAID3
7
SSAID2
6
SSAID1
5
SSAID0
4
SLT
3
ART
2
SOZ
1
SOM
0
Default>>>
0
0
0
0
0
X
1
1