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88 Parallel SCSI Interface Product Manual, Rev. A
Only one logical unit number shall be identified per task. The initiator may send one or more IDENTIFY mes-
sages during a task. A second IDENTIFY message with a different value in the LUN field shall not be issued
before a BUS FREE phase; if a target receives a second IDENTIFY message with a different value in this field,
it shall cause an unexpected bus free (see Section
3.1.1.1) by generating a BUS FREE phase. Thus an initia-
tor may change the DISCPRIV bit, but shall not attempt to switch to another task. (See the DTDC field of the
physical disconnect/reconnect mode page in Seagate SCSI Command Reference Manual, Part number
100293068 for additional controls over physical disconnection.)
An implied RESTORE POINTERS message shall be performed by the initiator following successful identifica-
tion of the nexus during the MESSAGE IN phase of a physical reconnection or a successful receipt of a SPI
L_Q information unit.
Identification is considered successful during an initial connection or an initiator’s physical reconnect when the
target detects no error during the transfer of the IDENTIFY message and an optional task attribute message in
the MESSAGE OUT phase following the SELECTION phase. See Section
4.4 for the ordering of the IDEN-
TIFY and TASK ATTRIBUTE messages. See Section 3.9.3.1 for handling target detected errors during the
MESSAGE OUT phase.
Identification is considered successful during a target’s physical reconnect when there is no attention condition
on either the IDENTIFY message or the simple message for an I_T_L_Q nexus in the MESSAGE IN phase fol
-
lowing the RESELECTION phase. See Section 4.5 for the ordering of the IDENTIFY and TASK ATTRIBUTE
messages. See Section 3.9.2.1, for handling target detected errors during the MESSAGE IN phase.
4.3.4 IGNORE WIDE RESIDUE
The IGNORE WIDE RESIDUE message (see Table 29) shall be sent from a target to indicate that the number
of valid bytes sent in the last REQ/ACK handshake data of a DATA IN phase is less than the negotiated trans-
fer width. When information unit transfers are disabled, the IGNORE WIDE RESIDUE message shall be sent
following that DATA IN phase and prior to any other messages.
If the residual byte contains valid data, then the IGNORE WIDE RESIDUE message should not be sent.
Table 29: IGNORE WIDE RESIDUE message format
The NUMBER OF BYTES TO IGNORE field indicates the number of invalid data bytes transferred. See Table
30.
Note. More than one IGNORE WIDE RESIDUE message may occur during a task.
Table 30: Ignore field definition
Bit
Byte
7 6 5 4 3 2 1 0
0 MESSAGE CODE (23H)
1 NUMBER OF BYTES TO IGNORE (01H)
Codes
Invalid data bits
Wide transfers
00h Reserved
01h DB(15-8)
02h Obsolete
03h Obsolete
04h-FFh Reserved