Transfer Period Factor Field - Fujitsu MAN3184 SERIES Specifications

Table 2.10
CODE
X'00'-X'08' Reserved
Transfer period equals 12.5ns (note 2). This code is only valid if the
X'09' PROTOCOL OPTIONS field has a value selected that supports double-
transition data transfers.
X'0A' Transfer period equals 25ns (note 3)
X'0B' Transfer period equals 50.0ns (note 3)
X'0C' Transfer period equals 50ns (note 4)
X'00'-X'18' Transfer period equals the period factor (note 4)
X'19'-X'31' Transfer period equals the period factor (note 5)
X'32'-X'FF' Transfer period equals the period factor (note 6)
Notes:
1. Faster timings may be allowed by future SCSI parallel interface standards.
2. Fast-80 data is latched every 12.5 ns.
3. Fast-40 data is latched every 25 ns or 50.0 ns.
4. Fast-20 data is latched using a transfer period of less than or equal 96 ns and greater than or
equal to 50 ns.
5. Fast-10 data is latched using a transfer period of less than or equal 196 ns and greater than
or equal 100 ns.
6. 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.
For ST synchronous data transfer the REQ/ACK OFFSET is the maximum number of REQ
assertions allowed to be outstanding before a corresponding ACK assertion is received at the
TARG. The size of a data transfer may be 1or 2 bytes depending on the values in the transfer
width exponent field.
For DT synchronous data transfer the REQ/ACK OFFSET is the maximum number of REQ
transitions allowed to be outstanding before a corresponding ACK transition is received at the
TARG. The size of a data transfer shall be 2 bytes.
See Section 1.5 for an explanation of the differences between DT and ST data transfers.
The REQ/ACK OFFSET value is chosen to prevent overflow conditions in the SCSI device's
reception buffer and offset counter.
asynchronous data transfer mode and that the PERIOD FACTOR field and the PROTOCOL
OPTIONS field shall be ignored; a value of FFh shall indicate unlimited REQ/ACK offset.
The TRANSFER WIDTH EXPONENT field defines the transfer width to be used during DATA
IN phases, and DATA OUT phases. The transfer width that is established applies to all logical
units on both SCSI devices.
Valid transfer widths are 8 bits (m=00h) and 16 bits (m=01h) if all the protocol options bits are
zero. The only valid transfer width is 16 bits (m=01h) if any of the protocol options bits are one.
TRANSFER WIDTH EXPONENT field values greater than 01h are reserved.
The protocol options bits (IU_REQ, DT_REQ, and QAS_REQ) are used by the originating SCSI
device to indicate the protocol options to be enabled. The responding SCSI device uses the
protocol options bits to indicate the protocol options requested by the originating SCSI device the
responding SCSI device has enabled.

TRANSFER PERIOD FACTOR field

DESCRIPTION
A REQ/ACK OFFSET value of zero shall indicate
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