Open SCSI Integrator's Manual for NonStop S-Series Servers

The SCSI SAC
Open SCSI Integrator’s Manual for NonStop Servers—422988-002
7-7
Termination Sequence
Termination Sequence
The termination sequence is initiated by the SCSI SAC to terminate a SCSI operation.
The SCSI SAC enters this sequence when it detects an error affecting the SCSI
operation or when it must perform a soft reset. The SCSI SAC can enter this sequence
from any other sequence except during the arbitration phase or bus-free phase.
The SCSI SAC asserts the ATN signal, then waits for the target to make the transition to
the message-out phase. An Abort message is sent by the SCSI SAC when the target
enters the message-out phase.
A SCSI bus-hung condition could occur if the target does not respond to the ATN signal.
The host should use the SCSI Abort or SCSI Bus Device Reset command to make sure
the SCSI operation is terminated and to check for a bus-hung condition.
SCSI-2 Messages Supported
The SCSI SAC supports a subset of the SCSI-2 message system to communicate with a
target and manage the SCSI interface. Table 7-3 lists this message subset. A discussion
of each supported message (in order by hexadecimal code) follows the table.
Note. Unsupported messages received from the target are rejected by the SCSI SAC with a
Message Reject message.
Table 7-3. SCSI-2 Messages Supported by the SCSI SAC
SCSI-2
Message
Code (hex)
Extended
Message
Code (hex) Message Direction
00h
- Command Complete In
01h
01h Synchronous Data Transfer Request In/Out
02h
- Save Data Pointer In
03h
- Restore Pointers In
04h
- Disconnect In
05h
- Initiator Detected Error Out
06h
- Abort Out
07h
- Message Reject In/Out
08h
- No Operation Out
09h
- Message Parity Error Out
0Dh
- Bus Device Reset Out
80h
- Identify In/Out