
MOTOROLA
Chapter 14. Power Management
14-9
Peripheral Logic Power Management
In doze mode, the PLL is fully operational and locked to PCI_SYNC_IN. The transition to
the full power state takes only a few processor clock cycles. The peripheral logic doze mode
operates totally independently from the power saving state of the processor.
14.3.1.3 Peripheral Logic Nap Mode
Further power saving from doze mode can be guaranteed through the peripheral logic nap
mode because the peripheral logic does not enter the nap mode unless the processor core is
in either nap or sleep mode.
As in peripheral logic doze mode, all peripheral logic functional units are disabled except
for PCI address decoding, the PCI bus arbiter, system RAM refreshing, processor bus
request monitoring, and NMI signal monitoring. Also, the EPIC and I
2
C units continue to
function.
When the nap mode is entered, a PCI transaction referenced to the system memory, a
processor bus request the assertion of NMI (PICR1[MCP_EN] must be set to recognize
NMI), or a hard reset brings the peripheral logic out of the nap mode and into the full-power
state.
14.3.1.3.1 PCI Transactions During Nap Mode
When the peripheral logic is awakened from the nap state by a PCI-agent initiated
transaction, the transaction is serviced, PMCR[PM] remains set, QACK does not negate (so
the processor core does not wake from nap or sleep), and the peripheral logic goes back to
the nap state after the transaction has been serviced. If the peripheral logic is awakened by
any other cause, PMCR[PM] is cleared, preventing the peripheral logic from automatically
re-entering the nap state.
Note that if the MPC8240 is temporarily awakened to service a PCI transaction, the
processor core is still in either nap or sleep mode; therefore, it does not respond to any
snoop cycles. Software should therefore ush the L1 cache before allowing the peripheral
logic to enter the nap mode if the system allows PCI accesses to wake up the peripheral
logic without waking the processor core.
14.3.1.3.2 PLL Operation During Nap Mode
In peripheral logic nap mode, the PLL is fully operational and locked to PCI_SYNC_IN.
The transition to the full-power state should take no more than a few processor cycles.
14.3.1.4 Peripheral Logic Sleep Mode
Peripheral logic sleep mode provides further power saving compared to the nap mode.
Similar to nap mode, the peripheral logic does not enter the sleep mode unless the processor
core has requested to enter either nap or sleep mode.
In peripheral logic sleep mode, no functional units are operating except the on-chip PCI bus
arbiter, system RAM refreshing logic (enabled by PMCR[LP_REF_EN] for sleep mode),
processor bus request monitoring, NMI signal monitoring, the EPIC unit, and the I
2
C unit.
Similar to nap mode, a processor bus request (provided PMCR[CKO_SEL] is set and the