Save Data Pointer (02H); Restore Pointers (03H); Disconnect (04H); Initiator Detected Error (05H) - Sony DDS-4 Product Description Manual

5. SCSI INTERFACE
The implied transfer width agreement shall remain in effect until a BUS DEVICE RESET message is received, until a
hard reset condition occurs, or until one of the two SCSI devices elects to modify the agreement. The default data
transfer width is eight-bit data transfer mode. The default data transfer mode is entered at power on m, after a BUS
DEVICE RESET message, or after a hard reset condition.

5. 3. 3 SAVE DATA POINTER (02h)

This message is sent from a target to the initiator at the end of a Data Phase to request that the initiator save a copy of the
present active data pointer for the currently attached logical unit.
As a target, it will send this message prior to a disconnect.
When received as a target, it will be handled as an illegal message, the unit will return MESSAGE REJECT and will
continue

5. 3 .4 RESTORE POINTERS (03h)

This message is sent from a target to direct the initiator to restore the most recently saved pointers for the currently
attached logical unit to the active state. Pointers to the command, data, and status locations for the logical unit will be
restored to the active pointers. Command and status pointers will be restored to the beginning of the present command
and status areas. The data pointer will be restored to the value at the beginning of the data area in the absence of a SAVE
DATA POINTER message or to the value at the point at which the last SAVE DATA POINTER message occurred for
that logical unit.
The unit sends a RESTORE POINTERS message before resending a previously unsuccessful status or data transfer. It
doesn't send a RESTORE POINTERS for re-selection but relies on the implicit restore pointers in a re-selection.
When received as a target, it will be handled as an illegal message; the unit will return MESSAGE REJECT and will
continue.

5. 3. 5 DISCONNECT (04h)

This message is sent from a target to inform an initiator that the present physical path is going to be broken (the target
plans to disconnect by releasing BSY). Later, reselection will be required in order to complete the current operation.
Note: The initiator detects a catastrophic error condition when the BUS FREE phase occurs (other than as result of a
RESET condition) without first receiving a DISCONNECT or COMMAND COMPLETE message. If the target
intentionally creates this condition, the target clears the current command. This message does not cause the
initiator to save the data pointer.
As a target, the unit supports this message and will disconnect if allowed by the initiator.
When received as a target, it will be handled as an illegal message; the unit will return MESSAGE REJECT and will
continue.

5. 3. 6 INITIATOR DETECTED ERROR (05h)

This message is sent from an initiator to inform a target that an error (e.g.: parity error) has occurred that does not prevent
the target from re-trying the operation. At this point, present pointer integrity is not assured. A RESTORE POINTERS
message or a disconnect followed by a reselection, will cause the pointers to be restored to their previously defined state.
When received as a target the unit will attempt to retry the phase and if unsuccessful then enter the status phase reporting
CHECK CONDITION with the sense key set to COMMAND ABORTED.
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