
Operating Registers
SYM53C810A Data Manual
5-45
Register 4D (CD)
SCSI Test One (ST EST 1)
Read/Write
Bit 7
SCLK
T his bit, when set, disables the external SCLK
(SCSI Clock) pin, and causes the chip to use
the PCI clock as the internal SCSI clock. If a
transfer rate of 10 MB/s is to be achieved on
the SCSI bus, this bit must be cleared and the
chip must be connected to at least a 40 MHz
external SCLK .
Bit 6
SISO (SCSI Isolation Mode)
T his bit allows the SYM53C810A to put the
SCSI bi-directional and input pins into a low
power mode when the SCSI bus is not in use.
When this bit is set, the SCSI bus inputs are
logically isolated from the SCSI bus.
Bits 5-0 Reserved
Register 4E (CE)
SCSI Test Two (ST EST 2)
Read/Write
Bit 7
SCE (SCSI Control E nable)
T his bit, when set, allows all SCSI control and
data lines to be asserted through the SOCL
and SODL registers regardless of whether the
SYM53C810A is configured as a target or ini-
tiator.
Note: this bit should not be set during normal
operation, since it could cause contention
on the SCSI bus. It is included for
diagnostic purposes only.
Bit 6
ROF (Reset SCSI Offset)
Setting this bit clears any outstanding synchro-
nous SREQ/SACK offset. T his bit should be
set if a SCSI gross error condition occurs, to
clear the offset when a synchronous transfer
does not complete successfully. T he bit auto-
matically clears itself after resetting the syn-
chronous offset.
Bit 5
Reserved
Bit 4
SLB (SCSI Loopback Mode)
Setting this bit allows the SYM53C810A to
perform SCSI loopback diagnostics. T hat is, it
enables the SCSI core to simultaneously per-
form as both initiator and target.
Bit 3
SZM (SCSI High-Impedance Mode)
Setting this bit places all the open-drain
48 mA SCSI drivers into a high-impedance
state. T his is to allow internal loopback mode
operation without affecting the SCSI bus.
Bit 2
Reserved
SCLK
7
SISO
6
RES
5
RES
4
RES
3
RES
2
RES
1
RES
0
Default>>>
0
0
X
X
X
X
X
X
SCE
7
ROF
6
RES
5
SLB
4
SZM
3
RES
2
EXT
1
LOW
0
Default>>>
0
0
X
0
0
X
0
0