
MOTOROLA
Chapter 1. Overview
1-7
1.3 Power Management
The MPC105 provides hardware support for four levels of power reduction; the nap, doze,
and sleep modes are invoked by register programming, and the suspend mode is invoked by
assertion of an external signal. The design of the MPC105 is fully static, allowing internal
logic states to be preserved during all power saving modes. The following sections describe
the programmable power modes provided by the MPC105.
1.3.1 Full-On Mode
This is the default power state of the MPC105 following a hard reset, with all internal
functional units fully powered and operating at full clock speed.
1.3.2 Doze Mode
In the doze power saving mode, all the MPC105 functional units are disabled except for PCI
address decoding, system RAM refreshing, and the CPU bus request monitoring (through
BR
n
). Once the doze mode is entered, a hard reset, a PCI transaction referenced to system
memory, or a bus request can bring the MPC105 out of the doze mode and into the full-on
state. If the MPC105 is awakened for a processor or PCI bus access, the access is completed
and the MPC105 returns to the doze mode. The doze mode is totally independent of the
power saving mode of the processor.
1.3.3 Nap Mode
Further power savings can be achieved through the nap mode, when both the processor and
the MPC105 are placed in a power reduction mode. In this mode, only the PCI address
decoding, system RAM refreshing, and the processor bus request monitoring are still
operating. Hard reset, a PCI bus transaction referenced to system memory, or a bus request
can bring the MPC105 out of the nap mode. If the MPC105 is awakened by a PCI access,
the access is completed, and the MPC105 returns to the nap mode. If the MPC105 is
awakened by a processor access, the access is completed, but the MPC105 remains in the
full-on state. When in the nap mode, the PLL (phase-locked loop) is required to be running
and locked to the system clock (SYSCLK).
1.3.4 Sleep Mode
Sleep mode provides further power savings compared to the nap mode. As in nap mode,
both the processor and the MPC105 are placed in a reduced power mode concurrently. In
sleep mode, no functional units are operating except the system RAM refresh logic, which
can continue (optionally) to perform the refresh cycles. A hard reset or a bus request wakes
the MPC105 from the sleep mode. The PLL and SYSCLK inputs may be disabled by an
external power management controller (PMC). For additional power savings, the PLL can
be disabled by configuring the PLL0–PLL3 pins into the PLL bypass mode. When
recovering from sleep mode, the external power management controller has to re-enable the
PLL and SYSCLK first, and then wake up the system after allowing the PLL time to relock.