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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 and 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 becomes true at the initiator, the initiator may
change or release the DB(7-0,P) signals and shall negate the ACK
INTERFACE
signal. After the ACK signal is false the target may continue the
transfer by asserting the REQ signal, as described above.
Synchronous Data Transfer
Synchronous data transfer is optional and is only used data phases. It
shall be used in a data phase if a synchronous data transfer agreement
has been established (see SYCHRONOUS DATA TRANSFER
REQUEST Message). The agreement specifies the REQ/ACK offset
and the minimum transfer period.
The REQ/ACK offset specifies the maximum number of REQ pulses
that can be sent by the target in advance of the number of ACK
pulses received from initiator, establishing a pacing mechanism. If
the number of REQ pulses exceeds the number of ACK pulses by the
REQ/ACK offset, the target shall not assert the REQ signal until
after the leading edge of the next ACK pulse is received. A
requirement for successful completion of the data phase is that the
number of ACK and REQ pulses be equal.
The target shall assert the REQ signal for a minimum of an assertion
period. The target shall then wait at least the greater of a transfer
period from the last transition of the REQ signal to true or a
minimum of a negation period from the last transition of the ACK
signal to false before asserting the ACK signal.
The initiator shall send one pulse on the ACK signal for each REQ
pulse received. The ACK signal may be asserted as soon as the
leading edge of the corresponding REQ pulse has been received. The
Initiator shall assert the ACK signal for a minimum of an assertion
period. The initiator shall wait at least the greater of transfer period
from the last transition of the ACK signal to true or for a minimum
of a negation period from the last transition of the ACK signal to
false before asserting the ACK signal.
M3099GX/GH OEM Manual
3-21
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