Information

• Shuts off Core Clock and System Clock to the ARM Cortex-M4 core immediately.
• Polls stop acknowledge indications from the non-core crossbar masters (DMA),
supporting peripherals (SPI, PIT) and the Flash Controller for indications that System
Clocks, Bus Clock and/or Flash Clock need to be left enabled to complete a
previously initiated operation, effectively stalling entry to the targeted low power
mode. When all acknowledges are detected, System Clock, Bus Clock and Flash
Clock are turned off at the same time.
• MCG and Mode Controller shut off clock sources and/or the internal supplies driven
from the on-chip regulator as defined for the targeted low power mode.
In wait modes, most of the system clocks are not affected by the low power mode entry.
The Core Clock to the ARM Cortex-M4 core is shut off. Some modules support stop-in-
wait functionality and have their clocks disabled under these configurations.
The debugger modules support a transition from stop, wait, VLPS, and VLPW back to a
halted state when the debugger is enabled. This transition is initiated by setting the Debug
Request bit in MDM-AP control register. As part of this transition, system clocking is re-
established and is equivalent to normal run/VLPR mode clocking configuration.
7.6 Module Operation in Low Power Modes
The following table illustrates the functionality of each module while the chip is in each
of the low power modes. (Debug modules are discussed separately; see Debug in Low
Power Modes.) Number ratings (such as 2 MHz and 1 Mbps) represent the maximum
frequencies or maximum data rates per mode. Also, these terms are used:
• FF = Full functionality. In VLPR and VLPW the system frequency is limited, but if a
module does not have a limitation in its functionality, it is still listed as FF.
• static = Module register states and associated memories are retained.
• powered = Memory is powered to retain contents.
• low power = Flash has a low power state that retains configuration registers to
support faster wakeup.
• OFF = Modules are powered off; module is in reset state upon wakeup.
• wakeup = Modules can serve as a wakeup source for the chip.
Table 7-2. Module operation in low power modes
Modules Stop VLPR VLPW VLPS LLS VLLSx
Core modules
NVIC static FF FF static static OFF
System modules
Table continues on the next page...
Module Operation in Low Power Modes
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
170 Freescale Semiconductor, Inc.