Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
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When the target is ready to transfer data for a disconnected I/O process for which a TTD message has been
sent, the target shall reconnect to the initiator for the I/O process (via a RESELECTION phase, an IDENTIFY
message, and an optional SIMPLE QUEUE TAG message), send a DISCONNECT message, and, if the
initiator does not respond with a MESSAGE REJECT message, go to the BUS FREE phase. This connection
serves to notify the initiator that the I/O process is ready for data transfer. If the initiator rejects the DISCON-
NECT message, the target may enter a data phase; otherwise, the initiator may reconnect to the I/O process
as described in the CONTINUE I/O PROCESS message (see above) to do the data transfer.
Initiators should avoid sending the TTD message to targets which have not implemented this message. Such
targets may not respond as described in this section. An initiator can determine whether a target implements
this message by examining the TranDis bit in the standard INQUIRY data (see 5.1.1.3).
3.5.3.2
Extended message (01h)
Extended messages are messages that require more than two bytes to send the necessary information. The
Extended messages supported by the disc drive are Modify Data Pointer and Synchronous Data Transfer.
These two are described in detail in the following paragraphs.
MODIFY DATA POINTERS MESSAGE
Table 3.5.3-3. Modify data pointer
Byte
Value
Description
0
01h
Extended message
1
05h
Extended message length
2
00h
MODIFY DATA POINTER code
3
Argument (Most Significant Byte)
4
Argument
5
Argument
6
Argument (Lease Significant Byte)
The MODIFY DATA POINTER message (Table 3.5.3-3) is sent from the target to the initiator and requests
that the signed argument be added (two’s complement) to the value of the current data pointer.
