
Register Descriptions
4-5
WATN
Select with ATN/ on a Start Sequence
When this bit is set, the SCSI ATN/ signal is asserted
during the selection phase (ATN/ is asserted at the same
time BSY/ is deasserted while selecting a target). If a
selection time-out occurs while attempting to select a
target device, ATN/ is deasserted at the same time SEL/
is deasserted. When this bit is cleared, the ATN/ signal is
not asserted during selection. When executing SCSI
SCRIPTS, this bit is controlled by the SCRIPTS
processor, but manual setting is possible in low level
mode.
4
EPC
Enable Parity Checking
When this bit is set, the SCSI data bus is checked for odd
parity when data is received from the SCSI bus in either
initiator or target mode. The host data bus is checked for
odd parity if bit 2, the Enable Parity Generation bit, is
cleared. Host data bus parity is checked as data is
loaded into the
SCSI Output Data Latch (SODL)
register
when sending SCSI data in either initiator or target mode.
If a parity error is detected, bit 0 of the
SCSI Status Zero
(SSTAT0)
register is set and an interrupt may be
generated.
3
If the SYM53C710 is operating in initiator mode and a
parity error is detected, assertion of ATN/ is optional, but
the transfer continues until the target changes phase.
When this bit is cleared, parity errors are not reported.
EPG
Enable Parity Generation/Parity Through
When this bit is set, the SCSI parity bit is generated by
the SYM53C710. The host data bus parity lines DP[3:0]
are ignored and should not be used as parity signals.
When this bit is cleared, the parity present on the host
data parity lines flow through the SYM53C710 internal
FIFOs and are driven onto the SCSI bus when sending
data (if the host bus is set to even parity, it is changed to
odd before it is sent to the SCSI bus). This bit is set to
enable the DP3_ABRT/ pin to function as an abort input
(ABRT/).
2
AAP
Assert ATN/ on Parity Error
When this bit is set, the SYM53C710 automatically
asserts the SCSI ATN/ signal upon detection of a parity
error. ATN/ is only asserted in initiator mode. The ATN/
1