Fujitsu M2488, Руководство по эксплуатации продукта

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SCSI MESSAGES M2488 PRODUCT GUIDE
3-4 CG00000-011503 REV. A April 1997
** NOTE **
The supported SCSI transfer rates are listed in Appendix G.
The originating device (the device that sends the first of the pair of SDTR messages) sets its values
according to the rules above to permit it to receive data successfully. If the responding device can
also receive data successfully with these values (or smaller transfer periods or larger REQ/ACK
offsets or both), it returns the same values in its SDTR message. If it requires a larger transfer
period, a smaller REQ/ACK offset, or both in order to receive data successfully, it substitutes val-
ues in its SDTR message as required, returning unchanged any value not required to be changed.
Each device when transmitting data respects the limits set by the other's SDTR message, but it is
permitted to transfer data with larger transfer periods, smaller REQ/ACK offsets, or both than
specified in the other's SDTR message. The successful completion of an exchange of SDTR mes-
sages implies an agreement as follows:
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 (a) 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 two
devices. For the MESSAGE PARITY ERROR case, the implied agreement shall be reinstated if a
retransmittal 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 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 transfers 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 initia-
tor 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 opera-
tion shall not be considered to exist until the target leaves the MESSAGE OUT phase, indicating
that the target has accepted the negotiation. After a vendor-specific number of retry attempts
Responding device SDTR response Implied agreement
a) Non-zero REQ/ACK offset Each device transmits data with a transfer period equal
to or greater than and a REQ/ACK offset equal to or
less than the values received in the other device's SDTR
message.
b) REQ/ACK offset equal to zero Asynchronous transfer
c) MESSAGE REJECT message Asynchronous transfer