
5.SCSI Interface
4.The I/O activity from this point is controlled entirely by the target. The target initiates the COMMAND phase and reads in the Command Descriptor Block (CDB) from the Host. If the Host has sent an Identify message with the Disconnect permission bit set, then the target will immediately disconnect from the bus after the entire CDB has been received.
5.The Disconnect process occurs when the target initiates a MESSAGE IN phase and sends a DISCONNECT message back to the Host. This message may be preceded by a SAVE DATA POINTERS message byte if the Disconnect is performed in the middle of the DATA phase. Following the MESSAGE IN phase, the target frees the bus by releasing the BSY.
6.The host now waits for the target to perform
7.When doing a large data transfer, the target may choose to divide the entire transfer into several smaller 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.
8.The Host may change Disconnect permission at any time after the SELECTION phase by asserting ATN and 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
The
Table 5-2: Message Descriptions
Code | Description |
| Direction | |
|
| In |
| Out |
00 | COMMAND COMPLETE | * |
|
|
01 | EXTENDED MESSAGE | * |
| * |
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 | * |
|
|
IDENTIFY | * |
| * |
SONY |