Chapter 8. Signal Descriptions
8-15
60x Bus Signal ConTguration
8.2.5 Address Transfer Termination Signals
The address transfer termination signals are used to indicate either that the address phase
of the transaction has completed successfully or must be repeated, and when it must be
terminated. For detailed information about how these signals interact, see Section 9.3.3,
òAddress Transfer Termination.ó
8.2.5.1 Address Acknowledge (AACK)Input
The address acknowledge (AACK) signal is an input-only signal on the MPC7400.
Following are the state meaning and timing comments for the AACK signal.
State Meaning
AssertedIndicates that the address phase of a transaction is
complete; the address bus is released to high-impedance on the next
bus clock cycle.
Note that the address tenure does not terminate until the assertion of
AACK, even if the associated data tenure has completed. As a
snooping device, the MPC7400 requires that AACK be asserted for
every assertion of TS that it detects.
Negated(During an address tenure) indicates that the address bus
and the transfer attributes must remain driven.
Timing Comments
AssertionMay occur as early as the bus clock cycle after TS is
asserted; assertion can be delayed to allow adequate address access
time for slow devices. For example, if an implementation supports
slow snooping devices, an external arbiter can postpone the assertion
of AACK.
NegationMust occur one bus clock cycle after the assertion of
AACK.
8.2.5.2 Address Retry (ARTRY)
The address retry (ARTRY) signal is both an input and output signal on the MPC7400.
8.2.5.2.1 Address Retry (ARTRY)Output
Following are the state meaning and timing comments for the ARTRY output signal.
State Meaning
AssertedIndicates that the MPC7400, as a snooping device,
detects a condition in which a snooped address tenure must be
retried. If the MPC7400 needs to update memory as a result of the
snoop that caused the retry, the MPC7400 asserts BR in the bus clock
cycle following the assertion of ARTRY.
High ImpedanceIndicates that the MPC7400 does not need the
snooped address tenure to be retried.