Asynchronous Information Transfer - Fujitsu Scan Partner 300C Instruction Manual

Bus settle delay
BSY
SEL
C/D,
MSG, I/O
REQ
ACK
DB
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.
INFORMATION TRANSFER phase
Min. Ons
4-16
INFORMATION
TRANSFER phase
Bus settle delay