Quantum 10K II - Manual (Page 341)

Appendix B. SCSI Bus Signal Timing
B–20 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
9. The initiator waits at least the greater of the following periods before reasserting
ACK, (assuming that REQ/ACK offset is set to zero): a.) A transfer period from
the last transition of the ACK signal to true; b.) A negation period from the last
transition of the ACK signal to false.
10. Otherwise the initiator can wait for an undefined period beyond the last received
REQ pulse (or after the maximum, negotiated, offset has been reached) before
asserting ACK. Note that when the maximum offset is reached, the target
(drive) does not send any more REQ pulses until it receives at least one ACK
pulse (since the REQ pulses must never be ahead of the ACK pulses by more
than the offset).
11. Since the number of REQ and ACK pulses must be equal at the end of the
phase, the target does not change the phase until all required ACK pulses have
been received.
Initiator-to-Drive Transfer Procedure
1. Initiator transfers one byte for each REQ pulse received.
2. Drive asserts from one to fifteen REQ signals.
3. After receiving the leading edge of a REQ signal, initiator drives the DB (7–0,
P) signals to the desired values (if no offset is to be applied to the transfer). If a
REQ/ACK offset is used, the initiator waits up to the maximum, negotiated
offset before driving the data lines.
The DB (7–0, P) signals are held valid for at least one deskew delay plus one
Cable Skew Delay plus one Hold Period after the assertion of the ACK signal.
4. The initiator delays at least one Deskew Delay plus a Cable Skew Delay before
asserting an ACK pulse.
5. After a Skew plus a Deskew plus a Hold Period delay, the initiator can change
or release the DB (7–0, P) signals.
6. The initiator asserts the ACK signal for a minimum of one assertion period after
which the initiator can negate the ACK signal.
7. The Drive reads the DB (7–0, P) signals within one Hold period of ACK signal
going true.
8. The drive waits at least the greater of the following periods before again
asserting the REQ signal:
a. A transfer period from the last transition of the REQ signal to true.
b. A negation period from the last transition of the REQ signal to false.
9. The initiator waits at least the greater of the following periods before again
asserting the ACK signal unless an REQ/ACK offset greater than zero is used:
a. A transfer period from the last transition of the ACK signal to true.
b. A negation period from the last transition of the ACK signal to false.