CHAPTER 6: Low Power Consumption Mode
FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E 209
3.3 Operations in RTC Mode
In RTC mode, all oscillators stop except for the sub oscillator. All functions stop operating except for the
watch counter, the RTC and the Low Voltage Detection Circuit.
Functions of RTC Mode
CPU and on-chip memory
In RTC mode, the CPU clock supplied to the CPU, and the AHB bus clock supplied to the on-chip
memory and the DMA controller stop. However, data in the on-chip memory is retained. In addition, the
debug function stops.
Peripherals
In RTC mode, all APB bus clocks stop. Except for the watch counter, the RTC and the Low Voltage
Detection Circuit, all resources stop at their respective states they were in immediately before the CPU
transits to RTC mode.
Watch counter and RTC
The counting operation of the watch counter is not affected by the transition to RTC mode and the watch
counter continues its operation according to the settings set prior to the transition. But, the watch counter
cannot return to from the RTC mode due to the watch counter interrupt. The RTC is not affected by RTC
mode transition. The RTC continues its operation according to the settings set prior to transition to RTC
mode.
Oscillator clocks
Table 3-3 shows the status of each oscillator clock.
Resets and interrupts
Resets and interrupts can be used for returning from RTC mode.
External bus
The external bus stops in RTC mode.
Pin state
The SPL bit in the Standby Mode Control Register (STB_CTL) can control whether an external pin stays
at the state it was in immediately before the CPU transits to RTC mode or changes to high impedance
state.
Procedure for Setting RTC Mode
Execute the following procedure to make the CPU transit to RTC mode.
1. With 1 written to the SORDY bit in the System Clock Mode Status Register (SCM_STR), write "1" to the
RTCE bit in the RTC Mode Control Register (PMD_CTL).
2. Write 0x1ACC, 0 and 0b10 to the KEY bits, DTSM bit and STM bits in the Standby Mode Control
Register (STB_CTL) respectively. Set the state of each pin in RTC mode by using the SPL bit.
3. Write 1 to the SLEEPDEEP bit in the Cortex-M4F System Control Register.
4. Execute the WFI instruction or the WFE instruction.
To Next Page
Loading...
