Quantum Quantum Atlas 10K II 9.2/18.4/36.7/73.4 GB, Product Manual

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Appendix B. SCSI Bus Signal Timing
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives B–21
B.5.5.3 Wide Data Transfer
Wide Data Transfer is optional and can be used in the DATA phase only if a wide
transfer agreement is established. Wide data transfer is established by negotiations
between the initiator and drive using the Wide Data Transfer Request message. The
IWN bit in the Quantum (Vendor) Special Function Control page specifies which
device (drive or initiator) is to initiate the negotiations.
During 16-bit wide data transfers, the first logical data byte for each data phase is
transferred across the DB (0–7, P) signals and the second logical data byte is
transferred across the DB (15–8, P1) signals. Subsequent pairs of data bytes are
likewise transferred in parallel.
B.5.5.4 Signal Restrictions Between Phases
When the SCSI bus is between two information transfer phases, the following
restrictions apply to the SCSI bus signals:
• The BSY, SEL, REQ, and ACK, signals do not change.
• The C/D, I/O, MSG, and DATA BUS signals can change.
•
When changing the DATA BUS direction from out (initiator-driving) to in
(drive-driving), the drive delays driving the DATA BUS by at least a data release
delay plus one bus settle delay after asserting the I/O signal and the initiator
releases the DATA BUS no later than a data release delay after the transition of
the I/O signal to true.
•
When switching the DATA BUS from in to out, the drive releases the DATA
BUS no later than a deskew delay after negating the I/O signal.
•
The ATN and RST signals can change as defined under the descriptions for the
attention condition (see B.5.1) and reset condition (see B.5.2).
B.5.5.5 Message Out — Additional Conditions
If the drive detects one or more parity error(s) received, it can indicate its desire to
retry the message(s) by asserting the REQ signal after detecting the ATN signal has
gone false and prior to changing to any other phase. The initiator, upon detecting
this condition, re-sends all the previous message byte(s) in the same order as
previously sent during this phase. When re-sending more than one message byte, the
initiator asserts the ATN signal at least two deskew delays prior to asserting the
ACK signal on the first byte and maintains the ATN signal until the last byte is
sent.