A.3 Bus Phases
Appendix A-17
After the ACK signal is false, the target may continue the transfer by driving the DB
(7-0, P) signals and asserting the REQ signal, as previously described.
b. Asynchronous transfer from initiator to target
If the I/O signal is false (transfer to the target), the target shall request information by
asserting the REQ signal. The initiator shall drive the DB (7-0, P) signals to their
desired values, delay at least one deskew delay plus a cable skew delay then assert the
ACK signal. The initiator shall continue to drive the DB (7-0, P) signals until the REQ
signal is false. When the ACK signal becomes true at the target, the target shall read
the DB (7-0, P) signals then negate the REQ signal. When the REQ signal becomes
false at the initiator, the initiator may change or release the DB (7-0, P) signals and
shall negate the ACK signal. The target may continue the transfer by asserting the
REQ signal, as previously described.
deskew delay +
cable skew
deskew delay
+ cable skew
bus settle delay
BSY
SEL
C/D, MSG
REQ
ACK
DB
I/O
