Deskewing; Wide Transfer - Seagate Ultra 160 Product Manual

and
(e) shall hold the DB(15-0) signals valid for a minimum of one transmit hold time.
If the I/O signal is false (i.e., transfer to the SCSI target port), to receive SPI information units the SCSI target
port:
(a) shall read the value of the DB(15-0 signals within one receive hold time of the transition of the ACK
signal.
If write flow control is enabled and the current SPI data stream information unit is the last SPI data stream infor-
mation unit of the stream:
(a) the SCSI target port shall assert the P_CRCA signal a minimum of a flow control transmit setup
time before the end of the last information unit and shall keep the P_CRCA signal asserted for a flow
control transmit hold time;
(b) the SCSI target port shall not assert the P_CRCA signal until a minimum of a flow control hold time
after the end of the previous information unit; and
(c) the SCSI target port shall negate the P_CRCA signal a minimum of a flow control transmit setup
time before the start of the next information unit.
Note. The earlier in a SPI data stream information unit that the SCSI target port asserts the P_CRCA signal,
the better the SCSI initiator port may manage data pre-fetch.
As a result of a SPI information unit always being an even number of transfers, the REQ and ACK signals are
negated both before and after the transmission of the SPI information unit.
Paced information unit transfers exception handling conditions are defined in Section 3.5.2.2.1.1 and Section
3.5.2.2.1.2.
3.5.3.4

Deskewing

The deskewing technique used in the receiving SCSI device is vendor specific. Any technique that works with
the specified training pattern and complies with the specified receive skew compensation timing requirement is
allowed. Deskewing shall only be enabled for paced transfers.
3.5.4

Wide transfer

Wide data transfers shall be used for DT DATA phases. Wide data transfer may be used in the ST DATA phase
only if a wide transfer agreement is in effect (see section 4.3.18 or 4.3.12).
All SCSI devices shall support 8-bit narrow data transfers.
During narrow transfers, all information shall be transferred in bytes across the DB(7-0) and DB(P_CRCA) sig-
nals on the SCSI bus. At the receiving device the DB(15-8) (if present) and DB(P1) (if present) signals are
undefined.
During wide transfers, the first and second information bytes for each DATA phase shall be transferred across
the DB(7-0) and DB(15-8) signals, respectively, on the SCSI bus. Subsequent pairs of information bytes are
likewise transferred in parallel across the SCSI bus (see Table 22).
The IGNORE WIDE RESIDUE message may be used to indicate that the last byte of a data field or the last
data byte of information unit is undefined.
74 Parallel SCSI Interface Product Manual, Rev. A