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Following target response (1) above, the implied agreement for wide data transfers shall be considered to be
negated by both the initiator and the target if it the initiator asserts ATN and the first message out is either MESSAGE
PARITY ERROR or MESSAGE REJECT. In this case, both devices shall go to eight-bit data transfer mode for data
transfers between the two devices. For the MESSAGE PARITY ERROR case, the implied agreement shall be
reinstated if a re-transmittal of the second of the pair of messages is successfully accomplished. After a
vendor-specific number of retry attempts (greater than ZERO), if the target receives a MESSAGE PARITY ERROR
message, it shall terminate the retry activity. This may be done either by changing to any other information transfer
phase and transferring at least on byte of information or by going to the BUS FREE phase. The initiator shall accept
such action as aborting the negotiation and both devices shall go to eight -bit data transfer mode for data transfers
between the two devices.
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.
SAVE DATA POINTER (02h)
5.3.3.
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. The unit will accept this message when in the
initiator mode. 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 enter the status phase reporting
CHECK CONDITION with the sense key set to COMMAND ABORTED.
RESTORE POINTERS (03h)
5.3.4.
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. Rather, it relies on the implicit restore pointers inherent in a
re-selection.
When acting as initiator, the unit will accept 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 re-selection.
When received as a target, it will be handled as an illegal message; the unit will return MESSAGE REJECT and will
continue.
DISCONNECT (04h)
5.3.5.
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, reelection 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.
The unit will support this message as an initiator. 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.
SONY AIT-4 drive SDX-900V series Ver.2.1
5.SCSI Interface
5-9
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