Chapter 8. Signal Descriptions
8-47
Non-Protocol Signal Descriptions
8.5.4.3 Quiescent Request (QREQ)Output
The quiescent request (QREQ) signal is an output signal on the MPC7400. See Chapter 10,
òPower and Thermal Management,ó for more information about the power management
modes of the MPC7400. Following are the state meaning and timing comments for the
QREQ signal.
State Meaning
AssertedIndicates that the MPC7400 is requesting all bus activity
to terminate or pause so that it may enter a quiescent (low-power)
state. Once in this state, the MPC7400 stops snooping further bus
activity
.
NegatedIndicates that the MPC7400 is not requesting to enter a
quiescent state.
Timing Comments
Assertion/NegationMay occur on any cycle. QREQ remains
asserted for the duration of the quiescent state.
8.5.4.4 Quiescent Acknowledge (QACK)Input
The quiescent acknowledge (QACK) signal is an input signal on the MPC7400. See
Chapter 10, òPower and Thermal Management,ó for more information about the power
management modes of the MPC7400. Following are the state meaning and timing
comments for the QACK signal.
State Meaning
AssertedIndicates that all bus activity has terminated or paused,
and the MPC7400 may enter nap or sleep mode.
NegatedIndicates that the MPC7400 may not enter nap or sleep
mode, or it must return to doze mode from nap mode in order to
snoop.
Timing Comments
Assertion/NegationMay occur on any cycle following the
assertion of QREQ. When negated for at least 8 bus cycles; it ensures
that the MPC7400 has returned to doze mode from nap mode.
8.5.4.5 Enhanced Mode (EMODE)Input
The enhanced mode (EMODE) signal is an input signal on the MPC7400 sampled at
HRESET negation used to select the MPX bus mode operation. The state of EMODE
sampled at HRESET negation is stored and readable from the EMODE bit in MSSCR0. The
state of MSSR0[EMODE] is active high, meaning that if EMODE is detected as asserted at
the negation of HRESET, MSSR0[EMODE] = 1. Section 9.6, òMPX Bus Protocol,ó
describes the MPX bus mode operation on the MPC7400.
The EMODE signal is also used to select address bus driven mode after HRESET is negated
in MPX bus mode. If EMODE is asserted after HRESET is negated, address bus driven
mode is selected; if EMODE is negated after HRESET is negated, normal address bus
driving mode (address bus not always driven) is selected. The address bus driven mode is
stored and readable from the MSSCR0[ABD] bit. See Section 9.6.1.2.1, òAddress Bus