Sony DDS-4, Product Description Manual

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5 - 7 SONY SDT-10000/SDT-11000 DDS Tape Drive
5. SCSI INTERFACE
Following target response (1) above, the implied agreement for synchronous operation shall be considered to be negated
by both the initiator and the target if the initiator asserts the ATN signal and the first message out is either MESSAGE
PARITY ERROR or MESSAGE REJECT. In this case, both devices shall go to asynchronous data transfer mode for
data transfers between the tow 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 two retry at-
tempts, 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 one 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 asynchronous data transfer mode for data transfer between the two devices.
If the target recognizes that negotiation is required, it sends an SDTR message to the initiator. Prior to releasing the ACK
signal on the last byte of the SDTR message from the target, the initiator shall assert the ATN signal and respond with its
SDTR message or with a MESSAGE REJECT message. If an abnormal condition prevents the initiator from returning
an appropriate response, both devices shall go to asynchronous data transfer mode for data transfers between the two
devices.
Following an initiator’s responding SDTR message, an implied agreement for synchronous operation shall not be con-
sidered to exist until the target leaves the MESSAGE OUT phase, indicating that the target has accepted the negotiation.
After two retry attempts, if the target has not received the initiator’s responding SDTR message, it shall go to the BUS
FREE phase without any further information transfer attempt. This indicates that a catastrophic error condition has
occurred. Both devices shall go to asynchronous data transfer mode for data transfer between the two devices.
If, following an initiator’s responding SDTR message, the target shifts to MESSAGE IN phase and the first message in
is MESSAGE REJECT, the implied agreement shall be considered to be negated and both devices shall go to asynchro-
nous data transfer mode for data transfers between the two devices.
The implied synchronous 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 mode is asynchronous data transfer mode. The default data transfer mode is entered at power on, after a BUS
DEVICE RESET message, or after a hard reset condition.
5. 3. 2. 2. WIDE DATA TRANSFER REQUEST
Byte Value Description
0 01h Extended message
1 03h Extended message length
2 01h WIDE DATA TRANSFER REQUEST code
3 m Transfer Width exponent
A WIDE DATA TRANSFER REQUEST (WDTR) message exchange shall be initiated by an SCSI device whenever a
previously-arranged transfer width agreement may have become invalid. The agreement becomes invalid after any
condition which may leave the data transfer agreement in an indeterminate state such as:
(1) after a hard reset condition
(2) after a BUS DEVICE RESET message and
(3) after a power cycle