PXD20RM Datasheet, PDF (1101/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

29.4.3.6 Clock sources (main voltage regulator independent) switch-on
On completion of the Processor Low-Power Mode Entry, the MC_ME controls all clock sources that affect
the system clock based on the <clock source>ON bits of the ME_<current mode>_MC and
ME_<target mode>_MC registers. The following system clock sources are switched on at this step:
• The fast internal RC oscillator (16 MHz)
• The fast external crystal oscillator (4–16 MHz)
• The secondary FMPLL
NOTE
Clock sources which need the main voltage regulator to be stable are not
controlled by this step.
The clock sources that are required by the target mode are switched on. The duration required for the
output clocks to be stable depends on the type of source, and all further steps of mode transition depending
on one or more of these clocks waits for the stable status of the respective clocks. The availability status
of these clocks is updated in the S_<clock source> bits of ME_GS register.
The clock sources which need to be switched off are unaffected during this process in order to not disturb
the system clock which might require one of these clocks before switching to a different target clock.
29.4.3.7 Main Voltage Regulator Switch-On
On completion of the Target Mode Request step, if the main voltage regulator needs to be switched on from
its off state based on the MVRON bit of the ME_<current mode>_MC and ME_<target mode>_MC
registers, the MC_ME requests the MC_PCU to power-up the regulator and waits for the output voltage
stable status in order to update the S_MVR bit of the ME_GS register.
This step is required only during the exit of the low-power modes HALT and STOP. In this step, the fast
internal RC oscillator (16 MHz) is switched on regardless of the target mode configuration, as the main
voltage regulator requires the 16 MHz int. RC osc. during power-up in order to generate the voltage status.
During the STANDBY exit sequence, the MC_PCU alone manages the power-up of the main voltage
regulator, and the MC_ME is kept in RESET or shut off (depending on the power domain #1 status).
29.4.3.8 Flash Module Switch-On
On completion of the Main Voltage Regulator Switch-On step, if the flash needs to be switched to normal
mode from its low-power or power-down mode based on the FLAON bit field of the
ME_<current mode>_MC and ME_<target mode>_MC registers, the MC_ME requests the flash to exit
from its low-power/power-down mode. When the flash available for access, the S_FLA bit field of the
ME_GS register updated to “11” by hardware.
If the main regulator is also off in device low-power modes, then during the exit sequence, the flash is kept
in its low-power state and is switched on only when the Main Voltage Regulator Switch-On process has
completed.
Freescale Semiconductor
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
29-43