Maxtor ATLAS 10K III Manual download pdf (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.

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