Seagate Ultra 320 - Manual (Page 106)

92 Parallel SCSI Interface Product Manual, Rev. A
4.3.12 PARALLEL PROTOCOL REQUEST
PARALLEL PROTOCOL REQUEST messages (see Table 33) are used to negotiate a synchronous data trans-
fer agreement, a wide data transfer agreement, and set the protocol options between two SCSI devices.
Table 33: PARALLEL PROTOCOL REQUEST message format
[1] For details on protocol option bits See Table 18, Section 2.12.8.
TRANSFER PERIOD FACTOR
00h-007h Reserved. Faster timings may be allowed by future SCSI parallel interface standards.
08h Transfer period equals 6.25 ns. Fast-160 data is latched every 6.25 ns.
09h Transfer period equals 12.5 ns. Fast-80 data is latched every 12.5 ns.
0Ah Transfer period equals 25 ns. Fast-40 data is latched every 25 ns or 30.3 ns.
0Bh Transfer period equals 30.3 ns. Fast-40 data is latched every 25 ns or 30.3 ns.
0Ch Transfer period equals 50 ns. Fast-20 data is latched using a transfer period of less than or equal to 96 ns and
greater than or equal to 50 ns.
ODh - 18h Transfer period equals the period factor x 4. Fast-20 data is latched using a transfer period of less than or
equal to 96 ns and greater than orequal to 50 ns.
19h - 31h Transfer period equals the period factor x 4. Fast-10 data is latched using a transfer period of less than or
equal to 196 ns and greater than or equal to 100 ns.
32h - FFh Transfer period equals the period factor x 4. Fast-5 data is latched using a transfer period of less than
or equal 1,020 ns and greater than or equal to 200 ns.
REQ/ACK OFFSET
This field determines the maximum number of REQs allowed to be outstanding before a correesponding ACK
is received at the target during synchronous or paced transfers.
For ST synchronous transfers, the REQ/ACK OFFSET is the number of REQ transitions that may be sent by
the target in advance of the number of ACK transitions received from the initiator.
For paced transfers in DT DATA IN phase, the REQ/ACK OFFSET is the number of data valid state REQ
assertions that may be sent by the target in advance of ACK assertions received from the initiator.
For paced transfers in DT DATA OUT phase, the REQ/ACK OFFSET is the number of REQ assertions that
may be sent by the target in advance of the number of data valid state ACK assertions received from the initia-
tor.
Bit
Byte
7 6 5 4 3 2 1 0
0 EXTENDED MESSAGE (01H)
1 EXTENDED MESSAGE LENGTH (06H)
2 PARALLEL PROTOCOL REQUEST (04H)
3 TRANSFER PERIOD FACTOR
4 RESERVED
5 REQ/ACK OFFEST
6 TRANSFER WIDTH EXPONENT (M)
7[1] PCOMP RTI RD_STRM WR_FLOW HOLD_MCS QAS_REQ DT_REQ IU_REQ