Information

Table 7-1. Chip power modes (continued)
Chip mode Description Core mode Normal
recovery
method
VLLS0 (Very
Low Leakage
Stop 0)
Most peripherals are disabled (with clocks stopped), but LLWU and
RTC can be used. NVIC is disabled; LLWU is used to wake up.
All of SRAM_U and SRAM_L are powered off. The 32-byte system
register file and the 32-byte VBAT register file remain powered for
customer-critical data.
The POR detect circuit can be optionally powered off.
Sleep Deep Wakeup Reset
2
BAT (backup
battery only)
The chip is powered down except for the VBAT supply. The RTC and
the 32-byte VBAT register file for customer-critical data remain
powered.
Off Power-up
Sequence
1. Resumes normal run mode operation by executing the LLWU interrupt service routine.
2. Follows the reset flow with the LLWU interrupt flag set for the NVIC.
7.3 Entering and exiting power modes
The WFI instruction invokes wait and stop modes for the chip. The processor exits the
low-power mode via an interrupt. The Nested Vectored Interrupt Controller (NVIC)
describes interrupt operation and what peripherals can cause interrupts.
NOTE
The WFE instruction can have the side effect of entering a low-
power mode, but that is not its intended usage. See ARM
documentation for more on the WFE instruction.
Recovery from VLLSx is through the wake-up Reset event. The chip wake-ups from
VLLSx by means of reset, an enabled pin or enabled module. See the table "LLWU
inputs" in the LLWU configuration section for a list of the sources.
The wake-up flow from VLLSx is through reset. The wakeup bit in the SRS registers in
the RCM is set indicating that the chip is recovering from a low power mode. Code
execution begins; however, the I/O pins are held in their pre low power mode entry
states, and the system oscillator and MCG registers are reset (even if EREFSTEN had
been set before entering VLLSx). Software must clear this hold by writing a 1 to the
ACKISO bit in the Regulator Status and Control Register in the PMC module.
NOTE
To avoid unwanted transitions on the pins, software must re-
initialize the I/O pins to their pre-low-power mode entry states
before releasing the hold.
Chapter 7 Power Management
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 167