Quantum ATL SuperLoader ATL, User Manual

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Chapter 2 Messages
Supported SCSI Messages
24 Quantum ATL SuperLoader Software Interface Guide
Figure 5 Wide Data
Transfer Request
Message
A WIDE DATA TRANSFER REQUEST message exchange is
initiated by a SCSI device whenever a previously arranged transfer
width agreement may have become invalid. The agreement
becomes invalid after any condition that may leave the data
transfer agreement in an indeterminate state such as
• After a hard reset condition
• After a BUS DEVICE RESET Message
• After a power cycle.
The WIDE DATA TRANSFER REQUEST message exchange
establishes an agreement between two SCSI devices on the width
of the data path to be 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 an 8-bit data path.
The SuperLoader implements both wide data transfer option and
synchronous data transfer option. It negotiates the wide data
transfer agreement 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.
Bit
Byte
7 6 5 4 3 2 1 0
0
Extended Message Identifier (01h) (see figure 1 )
1
Extended Message Length (02h)
2
WIDE DATA TRANSFER REQUEST (03h)
3
Transfer Width Exponent