Figure 3-4. Wdtr Message Format - Quantum DLT 1 Interface Manual

Figure 3-4
Bit
Byte
0
1
2
3

Figure 3-4. WDTR Message Format

A SCSI tape drive initiates a WDTR message exchange whenever a previously arranged transfer width
agreement may have become invalid. The agreement becomes invalid after any condition that leaves
the data transfer agreement in an indeterminate state:
After a hard reset condition
•
After a BUS DEVICE RESET message
•
After a power cycle.
•
The tape drive implements both the wide and synchronous data transfer options. It negotiates the wide
data transfer agreement before negotiating the synchronous data transfer agreement. If a synchronous
data transfer agreement is in effect, the tape drive resets the synchronous agreement to asynchronous
mode after accepting a WDTR message.
The transfer width is expressed as 2
width applies to all logical units. Valid transfer widths for the tape drive are 8 bits (m = 00h) and 16
bits (m = 01h). Values of m greater than (01h) are reserved.
81-81276-01 Rev A01
shows the format for this extended message.
7 6 5 4
Extended Message Identifier (01h)
Extended Message Length (02h)
WIDE DATA TRANSFER REQUEST (03h)
Transfer Width Exponent
n
where n is the transfer width in bytes. The established transfer
July 2004
DLT1/VS80 SCSI Interface Guide
3 2 1 0
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