WATN

Select with SATN/ on a Start Sequence

4

 

When this bit is set and the LSI53C875A is in the initiator

 

mode, the SATN/ signal is asserted during selection of a

 

SCSI target device. This is to inform the target that the

 

 

LSI53C875A has a message to send. If a selection

 

 

time-out occurs while attempting to select a target device,

 

SATN/ is deasserted at the same time SSEL/ is

 

 

deasserted. When this bit is cleared, the SATN/ 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.

 

EPC

Enable Parity Checking

3

 

When this bit is set, the SCSI data bus is checked for odd

 

parity when data is received from the SCSI bus in either

 

the initiator or target mode. If a parity error is detected,

 

 

bit 0 of the SCSI Interrupt Status Zero (SIST0) register is

 

set and an interrupt may be generated.

 

 

If the LSI53C875A is operating in the initiator mode and

 

a parity error is detected, assertion of SATN/ is optional,

 

but the transfer continues until the target changes phase.

 

When this bit is cleared, parity errors are not reported.

 

R

Reserved

2

AAP

Assert SATN/ on Parity Error

1

 

When this bit is set, the LSI53C875A automatically

 

 

asserts the SATN/ signal upon detection of a parity error.

 

SATN/ is only asserted in the initiator mode. The SATN/

 

signal is asserted before deasserting SACK/ during the

 

 

byte transfer with the parity error. Also set the Enable

 

 

Parity Checking bit for the LSI53C875A to assert SATN/

 

in this manner. A parity error is detected on data received

 

from the SCSI bus.

 

 

If the Assert SATN/ on Parity Error bit is cleared or the

 

 

Enable Parity Checking bit is cleared, SATN/ is not

 

 

automatically asserted on the SCSI bus when a parity

 

 

error is received.

 

TRGTarget Mode0

This bit determines the default operating mode of the LSI53C875A. The user must manually set the target or initiator mode. This is done using the SCRIPTS language

4-22Registers

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LSI 53C875A technical manual Watn, Epc, Aap