
Chapter 2. Signal Descriptions
2-25
Timing Comments
Assertion/Negation—Should be driven one cycle before the data bus
can be driven by the processor. May be asserted on any clock cycle
when the processor is driving, or will be driving, the data bus and
may remain asserted multiple cycles.
2.8 Data Transfer Termination Signals
Data termination signals are required after each data beat in a data transfer. Note that in a
single-beat transaction, the data termination signals also indicate the end of the tenure,
while in burst accesses, the data termination signals apply to individual beats and indicate
the end of the tenure only after the final data beat. For a detailed description of how these
signals interact, see Section 3.3.4, “Data Transfer Termination.”
2.8.1 Transfer Acknowledge (TA)—Input
Following are state and timing descriptions for the transfer acknowledge (TA) input signal.
State Meaning
Asserted—A single-beat data transfer or a data beat in a burst
transfer completed successfully (unless DRTRY is asserted on the
next bus clock cycle for reads). The TA signal must be asserted for
each data beat in a burst transaction.
Negated—Until TA is asserted, the master must continue driving the
data for the current write or must wait to sample the data for reads.
Timing Comments
Assertion—During a data tenure, which generally begins after a
qualified data bus grant and continues through the period defined by
DBB or DRTRY. This period is affected by the ARTRY window. See
Section 3.3.1.1, “Effect of ARTRY Assertion on Data Transfer and
Arbitration on the PowerPC 604 Processor.” The system can
withhold asserting TA to indicate that the master should insert wait
states to extend a data tenure.
Negation—Must occur after the bus clock cycle of the final (or only)
data beat of the transfer. For a burst transfer, the system can assert TA
for one bus clock cycle and then negate it to advance the burst
transfer to the next beat and insert wait states during the next beat.
When the 603 is configured for 1:1 clock mode and is performing a
burst read into data cache, the 603 requires one wait state between
the assertion of TS and the first assertion of TA for that transaction.
If no-DRTRY mode is also selected, the 603 requires two wait states.
2.8.2 Data Retry (DRTRY)—Input
Following are state and timing descriptions for the data retry (DRTRY) input signal.
State Meaning
Asserted—The master must invalidate the data from the previous
read operation. DRTRY is ignored for write transactions and is not
defined for direct-store transfers.