Parallel SCSI Interface Product Manual, Rev. A ) 43
2.12.5 Transfer period factor
The Transfer Period Factor field selects the transfer period and determines which transfer rate’s timing values
in Tables
5, 6, 7, and 8 shall be honored, provided that REQ/ACK OFFSET is greater than 00h. The field val-
ues are defined in Table 14.
Table 15 shows which transfer period factors may be used with different types of transfer agreements, provided
REQ/ACK OFFSET is greater than 00h.
Table abbreviations are defined as follows:
M = Mandatory: Support for the indicated transfer agreement shall be implemented if the indicated transfer
period factor is implemented.
O = Optional: Support for the indicated transfer agreement may be implemented if the indicated transfer
period factor is implemented.
NS = Not Supported: The indicated transfer agreement shall not be allowed if the indicated transfer factor is
selected.
Table 20 defines valid combinations of TRANSFER PERIOD FACTOR and other fields.
Table 14: Transfer period factor
Value
Description Message Transfer rate
00h - 06h Reserved N/A N/A
07h Transfer period equals 3.125 ns PPR Fast-320
08h Transfer period equals 6.25 ns PPR Fast-160
09h Transfer period equals 12.5 ns PPR Fast-80
0Ah Transfer period equals 25 ns PPR, SDTR Fast-40
0Bh Transfer period equals 30.3 ns PPR, SDTR Fast-40
0Ch Transfer period equals 50 ns PPR, SDTR Fast-20
0Dh - 18h Transfer period equals the TRANSFER PERIOD FACTOR x 4 PPR, SDTR Fast-20
19h - 31h Transfer period equals the TRANSFER PERIOD FACTOR x 4 PPR, SDTR Fast-10
32h - FFh Transfer period equals the TRANSFER PERIOD FACTOR x 4 PPR, SDTR Fast-5
Table 15: Transfer period factor relationships
Value
Transfer agreement
Synchronous Paced Data group
Information
unit
ST data DT data
00h - 06h Reserved
07h - 08h NS M NS M NS M
09h M NS O O NS M
0Ah M NS O O O O
0Bh M NS O O O O
0Ch M NS O O O O
0Dh - 18h M NS O O O O
19h - 31h M NS O O O O
32h - FFh M NS O O O O
