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Quantum DLT 7000 Tape System 4-13
4.2.16 WIDE DATA TRANSFER REQUEST Message (01h)
The following figure illustrates the message formats.
Bit
Byte
7 6 5 4 3 2 1 0
0 Extended Message Identifier (01h)
(see Figure 4-1)
1 Extended Message Length (02h)
2 WIDE DATA TRANSFER REQUEST
3 Transfer Width Exponent
Figure 4–5 Wide Data Transfer Request Message - Data Format
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 DLT 7000 tape drive 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.