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M3099GX/GH OEM Manual
The originating device (the device that sends the first of the pair of
SDTR message) 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 those 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 values in its SDTR message as required, returning
unchanged any value not required to be changed. Each device when
transmitting data shall respect 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 message implies an agreement as follows:
Responding Device SDTR response
1) Non-zero REQ/ACK offset
2) REQ/ACK offset equal to zero
3) MESSAGE REJECT message
See ANSI SCSI-2 6.6.21 for details of SYNCHRONOUS
TRANSFER REQUEST message.
Implied Agreement
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.
Asynchronous transfer
Asynchronous transfer
INTERFACE
3-109
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