Avago Technologies LSI53C1000R - Manual (Page 54)

2-24 Functional Description
Version 2.2 Copyright © 2000–2003 by LSI Logic Corporation. All rights reserved.
2.2.5.2 Parallel Protocol Request
CRC, Sync/Wide, DT, Quick Arbitration and Selection (QAS), and
“information units” are negotiated with a new SCSI extended message:
Transfer Period Factor (Byte 3) – Transfer Period Factor is the old
Synchronous Period value. These are the same with one addition for the
80 megatransfers/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).
Byte 0 0x01 Extended message
Byte 1 0x06 Length
Byte 2 0x04 Parallel Protocol Request (PPR)
Byte 3 0xXX Transfer Period Factor
Byte 4 0x00 Reserved
Byte 5 0xXX Req/Ack Offset
Byte 6 0xXX Transfer Width Exponent
Byte 7 0x0X Protocol options
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 4
×
Period =