Avago Technologies LSI53C1010R User Manual

Page 55

SCSI Functional Description

2-25

Version 2.2

Transfer Period Factor (Byte 3) – Transfer Period Factor is the old
Synchronous Period value. These are the same with one addition for the
80 megatransfer/s rate:

The transfer period depends on the data transfer speed, not the clock
period. So, in DT mode, 0x09 means 12.5 ns between clock edges,
which really means a 25 ns clock period. In DT mode, 0x0A means a
clock period of 50 ns but a data rate of 40 megatransfers/s (25 ns). In
ST mode, 0x0A means a clock period of 25 ns and a data rate of
40 megatransfers/s.

Req/ACK Offset (Byte 5) – Req/ACK Offset is the maximum SCSI offset.

Transfer Width Exponent (Byte 6) – Transfer Width Exponent is the
old width value. It is set to 0 (8-bit SCSI width) or 1 (16-bit SCSI width).

Note:

For DT mode or when the Protocol Options field is nonzero,
the Transfer Width Exponent must be one indicating a SCSI
width of 16 bits.

Note:

The Table Indirect data (used during selection/reselection)
must be updated to enable certain control bits in the
SCNTL4 register. Specific bits to look at include: bit 7,
U3EN (Ultra160 Transfer Enable); bit 6, AIPEN
(Asynchronous Information Protection Enable); and
bits [3:0] (Extra Clock Setup/Hold).

0x09

12.5 ns (Ultra160 SCSI) only valid when using DT

0x0A

25 ns (Ultra2 SCSI)

0x0B

30.3 ns

0x0C

50 ns (Ultra SCSI)

0x0D–0xFF

(in ns)

value

Period