
5-84
Registers
ROF
Reset SCSI Offset
6
Setting this bit clears any outstanding synchronous
SREQ/SACK offset. If a SCSI gross error condition
occurs, set this bit to clear the offset when a synchronous
transfer does not complete successfully. The bit
automatically clears itself after resetting the synchronous
offset.
DIF
SCSI Differential Mode
5
Setting this bit allows the SYM53C895 to interface
properly to external differential transceivers. Its only real
effect is to 3-State the SBSY/, SSEL/, and SRST/ pads
so that they can be used as pure inputs. This bit must be
cleared for single-ended or LVD operation. This bit should
be set in the initialization routine if the high voltage
differential interface is used.
SLB
SCSI Loopback Mode
4
Setting this bit allows the SYM53C895 to perform SCSI
loopback diagnostics. That is, it enables the SCSI core to
simultaneously perform as both initiator and target.
SZM
SCSI High-Impedance Mode
3
Setting this bit places all the open-drain 48 mA SCSI
drivers into a high-impedance state. This is to allow
internal loopback mode operation without affecting the
SCSI bus.
AWS
Always Wide SCSI
2
When this bit is set, all SCSI information transfers are
done in 16-bit wide mode. This includes data, message,
command, status and reserved phases. This bit should
normally be deasserted since 16-bit wide message,
command, and status phases are not supported by the
SCSI specications.
ExT
Extend SREQ/SACK Filtering
1
LSI Logic Symbios TolerANT SCSI receiver technology
includes a special digital lter on the SREQ/ and SACK/
pins that causes glitches on deasserting edges to be
disregarded. Setting this bit increases the ltering period
from 30 ns to 60 ns on the deasserting edge of the
SREQ/ and SACK/ signals.