Quantum Quantum Atlas 10K II 9.2/18.4/36.7/73.4 GB, Product Manual

Page: 350 / 371

Appendix B. SCSI Bus Signal Timing
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives B–29
B.8.5 CONTINUE TASK Message (12h) ( CONTINUE I/O PROCESS )
The CONTINUE TASK message tells the drive to resume the I/O that the initiator
has reconnected. This message is sent in the same MESSAGE OUT phase as the
IDENTIFY message.
B.8.6 DISCONNECT Message (04h)
The DISCONNECT message is sent from the drive to inform the initiator that the
present connection is going to be broken, i.e., the drive plans to disconnect by
releasing the BSY signal. A later reconnection will be required to complete the
current task. The message does not cause the initiator to save the current data
pointer. After sending the message, the drive goes to the BUS FREE phase by
releasing BSY.
The DISCONNECT message can also be sent by the initiator to tell the drive to
suspend the current phase and disconnect from the bus. The drive’s response and
handling of a DISCONNECT message is based on when, in the task, the initiator
sends the DISCONNECT message. Table B-13 summarizes the drive’s response.
Table B–13 Drive’s Response to DISCONNECT Message
BUS Phase Drive’s Response
SELECTION The drive discards the DISCONNECT message and goes to BUS FREE.
COMMAND The ATTENTION request is ignored while the Command Descriptor Block
is fetched; that is, the drive does not switch to MESSAGE OUT until after
all Command Descriptor Block bytes have been received. The drive
returns the DISCONNECT message, goes to BUS FREE, and reconnects to
resume the task based on the disconnect/reconnect parameters.
DATA The ATTENTION request is ignored until it is convenient to handle the
condition. For example, on reads and writes, the transfer of the current
host block is completed before handling the ATTENTION. The drive
honors the DISCONNECT message (sends SAVE DATA POINTER and
DISCONNECT messages) regardless of the amount of data remaining to
be sent for the current command.
STATUS IN The drive sends a MESSAGE REJECT message, switches back to MESSAGE
IN, and sends the TASK COMPLETE message.
B.8.7 IDENTIFY Message (80h - FFh)
The IDENTIFY message is sent by either the initiator or the drive to establish an
I_T_L nexus with the drive, under the conditions listed below. Figure B-2 shows the
format of the IDENTIFY message and Table B-14 describes the data field contents.