
2-32
PowerPC Microprocessor Family: The Bus Interface for 32-Bit Microprocessors
2.11.4 Quiescent Request (QREQ)—Output
Following are state and timing descriptions for the quiescent request (QREQ) output signal,
which the 603 uses to request that the system enter quiescent state.
State Meaning
Asserted—The 603 is requesting all bus activity normally required
to be snooped to terminate or to pause so the 603 may enter a low-
power (nap or sleep) state. Once the 603 has entered this state it no
longer snoops bus activity.
Negated—The 603 is not requesting to enter the quiescent state.
Assertion—Can occur at any time to indicate the request to enter the
quiescent state, during which the 603 keeps asserting QREQ.
Negation—Can occur whenever quiescent state is not requested.
Timing Comments
2.11.5 Quiescent Acknowledge (QACK)—Input
Following are state and timing descriptions for the quiescent acknowledge (QACK) input,
which the system uses to indicate to the 603 that it is ready to enter a low-power state.
State Meaning
Asserted—All bus activity that requires snooping has terminated or
paused so the 603 can enter a low-power state.
Negated—The 603 cannot enter a low-power state.
Assertion/Negation—May occur on any cycle after the assertion of
QREQ and must be held for a minimum of one bus clock cycle.
Start-up—QACK is sampled at the negation of HRESET to select
the reduced-pinout mode; if QACK is asserted at start-up, reduced-
pinout mode is disabled. See Section 6.4, “Reduced-Pinout Mode
(603),” for a description of the reduced pinout mode.
Timing Comments
2.11.6 Halted (HALTED)—Output
Following are state and timing descriptions for the HALTED output signal which the 604
uses to indicate to other system components that the processor has been halted.
State Meaning
Asserted—The 604 enters idle state as a result of the nap mode.
Dispatch and execution stops and the processor bus is idle.
Negated—The processor is not in the idle state.
Assertion/Negation—Synchronous with the processor clock.
Timing Comments
2.11.7 Run (RUN)—Input
Following are state and timing descriptions for the RUN input signal, which is used to
notify the 604 that snooping is required.