
MOTOROLA
Appendix A. Power Management
A-5
determine whether the refresh is a self refresh (MCCR8[SREN] set to 1) or a CBR refresh
(MCCR8[SREN] cleared to 0).
When the MPC105 is in the sleep mode using CBR refresh and keeping the PLL in locked
operation, the wake up latency should be comparable to nap mode. However, additional
wake up latency will be needed if the system uses the self refresh mode and/or turns off the
PLL during sleep mode operation.
Before entering the sleep mode, QREQ from 603 or HALT from 604 should be sampled
active. The MPC105 will then respond with a QACK signal when it is ready to enter the
sleep mode, thereby allowing the processor to enter into either the nap or sleep mode.
Turning off the PLL and/or external clock during sleep mode requires waiting until the
assertion of the QACK signal. The external PMC chip should trap all the wake up events so
that it can turn on the PLL (observing the recommended PLL relock time) and/or the
external clock source before forwarding the wake up event to the MPC105.
A.1.6 Suspend Mode
Suspend mode provides the greatest reduction of power consumption. It is activated
through the assertion of the SUSPEND signal, which is driven by an external I/O device (in
most cases an external (system level) power management controller). In suspend mode, no
functional units are operating except the system RAM refresh logic (optional) and the
internal logic monitoring the SUSPEND signal. The MPC105 will remain in the suspend
mode until the SUSPEND signal is negated.
The PLL and SYSCLK input may be disabled by an external power management controller
(PMC) for additional power savings. The PLL can be disabled by setting the
PLL_CFG[0–3] pins into the PLL bypass mode. When recovering from suspend mode, the
external PMC has to re-enable the PLL and SYSCLK first, and then wake up the system
after the PLL has had time to relock (100 microseconds).
In suspend mode, the system can retain the contents of system memory through the use of
three different methods. The first method is the low-frequency refresh (RTC refresh) which
can be supplied very easily by most systems. A low frequency clock signal is supplied by
the system to the real time clock (RTC) input of the MPC105. The second method is to
enable the self refresh mode of the system memory. This can be supported only if the
system memory is capable of supporting the self refresh mode. The third method is
supported by the operating system by copying all the system memory data to the hard disk.
In this case, there is no need to continue the memory refresh operation.
The programming options for the three memory retention methods is defined by the
configuration of PMCR[LP_REF_EN] and MCCR8[SREN]. If PMCR[LP_REF_EN] is
cleared to 0, there will be no memory refresh operation when the MPC105 is in suspend
mode. If PMCR[LP_REF_EN] is set to 1, memory refresh will be carried out even when
the MPC105 is in suspend mode.