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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.

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Quantum SuperLoader Guida Utente Pagina 40