Fujitsu MBA3073 SERIES Technical Manual page 193

Following a TARG's responding PARALLEL PROTOCOL REQUEST message, an implied
agreement for data transfers shall not be considered to exist until;
a) the INIT receives the last byte of the PARALLEL PROTOCOL REQUEST message and
parity is valid; and
b) the TARG does not detect an attention condition on the last byte of the PARALLEL
PROTOCOL REQUEST message.
If the INIT does not support the TARG's responding PARALLEL PROTOCOL REQUEST
message's values the INIT shall create an attention condition and the first message shall be a
MESSAGE REJECT message.
If during the PARALLEL PROTOCOL REQUEST message the INIT creates an attention
condition and the first message of the MESSAGE OUT phase is either a MESSAGE PARITY
ERROR or MESSAGE REJECT message the data transfers shall be considered to be negated by
both SCSI devices. In this case, both SCSI devices shall use the go to eight-bit/asynchronous data
transfer mode with all the protocol options bits set zero to indicate ST DATA IN and ST DATA
OUT phases for data transfers between the two SCSI devices.
186 C141-C015