Wide Data Transfer Request - Freecom TAPEWARE AIT-250I Specification

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Specifications (2 pages)

Specifications (2 pages)

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Table of Contents

5.SCSI Interface

Responding Device SDTR response

(1) Non-ZERO REQ/ACK offset

(2) REQ/ACK offset equal to ZERO

(3) MESSAGE REJECT message

If the initiator recognizes that negotiation is required, it asserts the ATN signal and sends a SDTR message to begin

the negotiating process. After successfully completing the MESSAGE OUT phase, the target shall respond with the

proper SDTR message. If an abnormal condition prevents the target from returning an appropriate response, both

devices shall go to asynchronous data transfer mode for data transfers between the two devices.

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 attempts, 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

considered 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

asynchronous 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.