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The INFORMATION TRANSFER phases use one or more REQ/ACK handshakes to control the information
transfer Each REQ/ACK handshake allows the transfer of one byte of information. During the
INFORMATION TRANSFER phases the BSY signal shall remain true and the SEL signal shall remain
false. Additionally, during the INFORMATION TRANSFER phases, the target shall continuously envelope
the REQ/ACK handshake(s) with the C/D, I/O and MSG signals in such a manner that these control signals
are valid for a bus settle delay before the assertion of the REQ signal of the first handshake. These control
signals remain valid until after the negation of the ACK signal at the end of the handshake of the last transfer
of the phase.
4.3.4.1 Asynchronous information transfer
The target shall control the direction of information transfer by means of the I/O signal. When the I/O
signal is true, information shall be transferred from the target to the initiator When the I/O signal is false,
information shall be transferred from the initiator to the target.
(a) Asynchronous transfer from target to initiator
If the I/O signal is true (transfer to the initiator), the target shall first drive the DB(7-O, P) signals to
their desired values, delay at least one deskew delay plus a cable skew delay then assert the REQ
signal. The DB (7-0, P) signals shall remain valid until the ACK signal is true at the target. The
initiator shall read the DB(7-0, P) signals after the REQ signal is true then indicate its acceptance of
the data by asserting the ACK signal. when the ACK signal becomes true at the target, the target
may change or release the DB(7-O P) signals and shall negate the REQ signal. After the REQ signal
is false, the initiator shall then negate the ACK signal.
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.
Bus settle delay Bus settle delayMin. Ons
BSY
SEL
REQ
ACK
DB
C/D,
MSG, I/O
INFORMATION
TRANSFER phase
INFORMATION TRANSFER phase