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SCSI Operating Registers
5-12
SYM53C875/875E Data Manual
Register 04 (84)
SCSI Chip ID (SCID)
Read/Write
Bit 7
Reserved
Bit 6
RRE (E nable Response to
Reselection)
When this bit is set, the SYM53C875 is
enabled to respond to bus-initiated reselection
at the chip ID in the RESPID0 and RESPID1
registers. Note that the SYM53C875 will not
automatically reconfigure itself to initiator
mode as a result of being reselected.
Bit 5
SRE (E nable Response to Selection)
When this bit is set, the SYM53C875 is able to
respond to bus-initiated selection at the chip
ID in the RESPID0 and RESPID1 registers.
Note that the SYM53C875 will not automati-
cally reconfigure itself to target mode as a
result of being selected.
Bit 4
Reserved
Bits 3-0 E ncoded Chip SCSI ID, bits 3-0
T hese bits are used to store the SYM53C875
encoded SCSI ID. T his is the ID which the
chip will assert when arbitrating for the SCSI
bus. T he IDs that the SYM53C875 will
respond to when being selected or reselected
are configured in the RESPID0 and RESPID1
registers. T he priority of the 16 possible IDs, in
descending order is:
Register 05 (85)
SCSI Transfer (SX FER)
Read/Write
Note: When using Table Indirect I/O commands,
bits 7-0 of this register will be loaded from
the I/O data structure.
Note: For additional information on how the
synchronous transfer rate is determined,
refer to Chapter 2, “Functional
Description.”
Bits 7-5 T P2-0 (SCSI Synchronous Transfer
Period)
T hese bits determine the SCSI synchronous
transfer period used by the SYM53C875 when
sending synchronous SCSI data in either initia-
tor or target mode. T hese bits control the pro-
grammable dividers in the chip.
Note: For Ultra SCSI transfers, the ideal transfer
period is 4, and 5 is acceptable. Setting the
transfer period to a value greater than 5 is
not recommended.
T he synchronous transfer period the
SYM53C875 should use when transferring
SCSI data is determined as in this exam-
RES
7
RRE
6
SRE
5
RES
4
ENC3
3
ENC2
2
ENC1
1
ENC0
0
Default>>>
X
0
0
X
0
0
0
0
Highest
4
Lowest
12
7
6
5
3
2
1
0
15
14
13
11
10
9
8
TP2
7
TP1
6
TP0
5
MO4
4
MO3
3
MO2
2
MO1
1
MO0
0
Default>>>
0
0
0
0
0
0
0
0
TP2
TP1
TP0
XFERP
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
4
5
6
7
8
9
10
11