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90 Parallel SCSI Interface Product Manual, Rev. A
It is recommended that the target not attempt to move the data pointer outside the range addressed by the
command. Initiators may or may not place further restrictions on the acceptable values. Should the target send
an Argument
value that is not supported by the initiator, the initiator may reject the value by responding with the
MESSAGE REJECT message. In this case, the data pointer is not changed from its value prior to the rejected
MODIFY DATA POINTER message.
If an information unit transfer agreement is in effect the target shall not transmit a MODIFY DATA POINTER
message.
Table 31: MODIFY DATA POINTER message format
4.3.10 MODIFY BIDIRECTIONAL DATA POINTER
The MODIFY BIDIRECTIONAL DATA POINTER message (see Table 32) is sent from the target to the initiator
and requests that the signed data-out argument be added using two’s complement arithmetic to the value of
the current data-out pointer and signed data-in argument be added using two’s complement arithmetic to the
value of the current data-in pointer. The ENABLE MODIFY DATA POINTER (EMDP) bit in the Disconnect-
reconnect mode page indicates whether the target is permitted to issue the MODIFY BIDIRECTIONAL DATA
POINTER message. The target shall only issue the MODIFY BIDIRECTIONAL DATA POINTER message dur
-
ing a bidirectional command.
It is recommended that the target not attempt to move the data-out pointer or the data-in pointer outside the
range addressed by the command. Initiators may or may not place further restrictions on the acceptable val
-
ues. Should the target send a data-out argument or a data-in argument value that is not supported by the initi-
ator, the initiator may reject the value by responding with the MESSAGE REJECT message. In this case, both
the data-out pointer and the data-in pointer are not changed from their values prior to the rejected MODIFY
BIDIRECTIONAL DATA POINTER message.
If an information unit transfer agreement is in effect the target shall not transmit a MODIFY DATA POINTER
message.
Bit
Byte
7 6 5 4 3 2 1 0
0 EXTENDED MESSAGE (01H)
1 EXTENDED MESSAGE LENGTH (05H)
2 MODIFY DATA POINTER (00H)
3 (MSB)
ARGUMENT
4
5
6 (LSB)