Quantum 10K II - Manual (Page 361)

Appendix B. SCSI Bus Signal Timing
B–40 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
B.8.24 PARALLEL PROTOCOL REQUEST Message (04h) (continued)
Table B–18 PARALLEL PROTOCOL REQUEST Message — Field Descriptions
Field Description
Transfer Period Factor Options are:
Code
Description
00h – 08h Reserved for faster timings that may be allowed in future
SCSI interface standards.
09h Transfer period = 12.5ns (Fast-80 data is latched every
12.5ns); valid only if the PROTOCOL OPTIONS field has a
value selected that supports double-transition data
transfers.
0Ah Transfer period = 25ns (Fast-40 data is latched every
25ns)
0Bh Transfer period = 30.3ns (Fast-40 data is latched every
30.3ns)
0Ch Transfer period = 50ns (Fast-20 data is latched using a
transfer period of less than or equal to 96ns and greater
than or equal to 50ns)
0Dh – 18h Transfer period = the period factor x 4 (Fast-20 data is
latched using a transfer period of less than or equal to
96ns and greater than or equal to 50ns)
19h – 31h Transfer period = the period factor x 4 (Fast-10 data is
latched using a transfer period of less than or equal to
196ns and greater than or equal to 100ns)
32h – FFh Transfer period = the period factor x 4 (Fast-5 data is
latched using a transfer period of less than or equal to
1020ns and greater than or equal to 200ns)
For best performance for an Atlas 10K IIdisk drive, the value of this field
is 09h
REQ / ACK Offset Request / Acknowledge Offset. For single transition (ST) synchronous
data transfers, the value of REQ/ACK Offset is the maximum number of
REQ assertions allowed to be outstanding before a related ACK
assertion is received at the target. The size of the data transfer may be 1
or 2 bytes, depending on the values in the Transfer Width Exponent
Field.
For dual transition (DT) synchronous data transfers, the value of
REQ/ACK Offset is the maximum number of REQ assertions allowed to
be outstanding before a related ACK assertion is received at the target.
The size of the data transfer will be 2 bytes.
For best performance for an Atlas 10K IIdisk drive, the value of this field
is 1Fh.
(continued)