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5.SCSI Interface
When doing a large data transfer, the target may choose to divide the entire transfer into several smaller
7.
transfers. This allows the target to free the SCSI bus whenever it needs to perform its own system tasks not
immediately related to the actual data transfer over the SCSI bus. The target will not lock the bus into the
DATA phase if it is not presently ready to efficiently execute the transfer. After the data transfer is completed,
the target enters a STATUS phase and sends a single status byte to the Host. It then proceeds to a MESSAGE
IN phase, during which the target sends a COMMAND COMPLETE message. Finally, the target frees the bus
and the current command is considered completed.
The Host may change Disconnect permission at any time after the SELECTION phase by asserting ATN and
8.
sending an Identify message via a MESSAGE OUT phase. If the Host, however, performs this action during a
DATA phase, it is possible that the target will not notice the change in Disconnect permission status until past
the end of the current bus phase.
5.3. Message Specification
This clause includes all SCSI messages. Both supported and non-supported messages are listed. Elements of this
clause come from clause 5, Logical Characteristics, of the SCSI standard. The message system allows
communication between an initiator and a target for the purpose of physical path management. The table below lists
the Messages supported by the SDX-550V.
The SDX-550V supports the Synchronous Data Transfer Request Extended Message, and the Wide Data Transfer
Request Message.
Code
00
COMMAND COMPLETE
01
EXTENDED MESSAGE (Note 1)
02
SAVE DATA POINTER
03
RESTORE POINTERS
04
DISCONNECT
05
INITIATOR DETECTED ERROR
06
ABORT
07
MESSAGE REJECT
08
NO OP
09
MESSAGE PARITY ERROR
0C
BUS DEVICE RESET
23
IGNORE WIDE RESIDUE
80-CO
IDENTIFY
COMMAND COMPLETE (00h)
5.3.1.
This message is sent from a target to an initiator to indicate that the execution of a command or a series of linked
commands has completed and valid status has been sent to the initiator. After successfully sending this message,
the target goes to the BUS FREE phase by releasing BSY.
When received as a target, it will be handled as an illegal message, the unit will return MESSAGE REJECT and will
enter the status phase reporting CHECK CONDITION with the sense key set to COMMAND ABORTED.
5-4
Table 5-2: Message Descriptions
Description
SONY AIT-2 Turbo drive SDX-550V series Ver.1.0
Direction
In
Out
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
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