Quantum 10K II - Manual (Page 358)

Appendix B. SCSI Bus Signal Timing
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives B–37
the drive detects the negation of ACK for the TASK COMPLETE message (with
ATN false), the drive goes to the BUS FREE phase by releasing the BSY signal. The
drive also negates the MSG, C/D and I/O signals at this time.
B.8.23 WIDE DATA TRANSFER REQUEST Message (03h)
The WDTR message exchange establishes an agreement between two SCSI devices
on the width of the data path used for DATA phase transfers between the two
devices. This agreement applies to DATA IN and DATA OUT phases only. All other
information transfer phases use an 8-bit data path.
If a SCSI device implements the wide data transfer option and the synchronous data
transfer option, then the device negotiates the wide data transfer agreement before
negotiating the synchronous data transfer agreement. If a synchronous data transfer
agreement is in effect, the SCSI device that accepts the WDTR message resets the
synchronous agreement to the asynchronous mode.
The agreement becomes invalid and reverts to an 8-bit data transfer after any
condition that can leave the data transfer agreement in an indeterminate state such
as:
•
After a hard reset,
• After a TARGET RESET message, and
• After a power cycle.
The format of the WIDE DATA TRANSFER REQUEST message is shown in Figure
B-5. The data is described in Table B–17.
Bit 7 6 5 4 3 2 1 0
Byte
0 Extended Message (01h)
(See Figure B–1)
1 Extended Message Length (02h)
2 WIDE DATA TRANSFER REQUEST code (03h)
3 Transfer Width
Figure B–5 WIDE DATA TRANSFER REQUEST Message — Data Format