Quantum ATL SuperLoader ATL, User Manual

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Chapter 2 Messages
Supported SCSI Messages
22 Quantum ATL SuperLoader Software Interface Guide
• After a BUS DEVICE RESET Message
• After a power cycle.
• After a WIDE DATA TRANSFER REQUEST message
exchange.
The SYNCHRONOUS DATA TRANSFER REQUEST message
exchange establishes an agreement between two SCSI devices on
the clocking of the data used for DATA phase transfer between
them. This agreement applies to DATA IN and DATA OUT phases
only. All other information transfer phases must use asynchronous
transfers.
The SuperLoader implements both wide data transfer option and
synchronous data transfer option. Wide data transfer must be
negotiated prior to negotiating the synchronous data transfer
agreement. If a synchronous data transfer agreement is in effect,
then after accepting a WIDE DATA TRANSFER REQUEST
message, it resets the synchronous agreement to asynchronous
mode.
If the Transfer Period requested is lower than the minimum value
supported by the device, the return value will be adjusted up to
the minimum supported value. All possible transfer periods
between the minimum and maximum values are not supported. If
the Transfer Period requested is between the minimum and
maximum supported values, but not exactly achievable by the
device, the returned value will be the request value and the
SuperLoader will transmit data at the next lower speed it is
capable of. The initiator may send data at the request speed. The
maximum supported synchronous period is 5Dh (372 nsec). A
request with a Transfer Period lower than this will return a request
for asynchronous mode.