Fujitsu MAN3184 SERIES Specifications page 150

(1) Target initiated PARALLEL PROTOCOL REQUEST negotiation
If the TARG recognizes that PARALLEL PROTOCOL REQUEST negotiation is required, it not
sends a PARALLEL PROTOCOL REQUEST message to the INIT.
(2) Initiator initiated PARALLEL PROTOCOL REQUEST negotiation
If the INIT recognizes that PARALLEL PROTOCOL REQUEST negotiation is required, it creates
an attention condition and sends a PARALLEL PROTOCOL REQUEST message to begin the
negotiating process. After successfully completing the MESSAGE OUT phase, the TARG shall
respond with a PARALLEL PROTOCOL REQUEST message or a MESSAGE REJECT message.
If an abnormal condition prevents the TARG from responding with a PARALLEL PROTOCOL
REQUEST message or with a MESSGE REJECT message then both SCSI devices shall use the
eight-bit/asynchronous data transfer mode with all the protocol options bits set zero to indicate ST
DATA IN and ST DATA OUT phases between the two SCSI devices.
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.
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