Auto-Wake-Up From Low-Power Mode; Table 55. Shutdown Mode - STMicroelectronics STM32WL5 Series Reference Manual

Power control (PWR)
In Shutdown mode, the following features can be selected by programming individual
control bits:
•
Real-time clock (RTC): this is configured by the RTCEN bit in the backup domain
control register (RCC_BDCR).
Caution: In case of V
•
External 32.768 kHz oscillator (LSE): this is configured by the LSEON bit in the backup
domain control register (RCC_BDCR)
Exit Shutdown mode
The Shutdown mode is exited according
exiting from Shutdown mode. All registers (except for the ones in the backup domain) are
reset after wake-up from Shutdown.
Refer to the table below for more details on how to exit Shutdown mode.
Shutdown mode
Mode entry
Mode exit
Wake-up latency
6.5.12

Auto-wake-up from low-power mode

The RTC can be used to wake up the MCU from low-power mode without depending on an
external interrupt (auto-wake-up mode). The RTC provides a programmable time base for
waking up from Stop (0, 1 or 2) or Standby mode at regular intervals. For this purpose, the
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power-down, the RTC content is lost.
DD

Table 55. Shutdown mode

WFI (wait for interrupt) or WFE (wait for event) while:
– SLEEPDEEP bit is set in Cortex system control register
– No interrupt (for WFI) or event (for WFE) is pending
– LPMS = 0b1xx in PWR_CR1 and PWR_C2CR1
– WUFx bits are cleared in power status register 1 (PWR_SR1)
On return from ISR while:
– SLEEPDEEP bit is set in Cortex system control register
– SLEEPONEXT = 1
– No interrupt is pending
– LPMS = 0b1xx in PWR_CR1 and PWR_C2CR1
– Radio IRQ is cleared in the sub-GHz radio.
– WPVDF, WRFBUSY and WUFx bits are cleared in power status register 1
(PWR_SR1)
– The RTC flag corresponding to the chosen wake-up source (RTC Alarm A,
RTC Alarm B, RTC wake-up, synchronous binary counter or timestamp
flags) is cleared
– TAMP flags ITAMPxF and TAMPxF are cleared.
WKUPx pin edge, RTC and TAMP event, external reset in
Reset phase
RM0453 Rev 5
Section 6.5.4. A power-on reset occurs when
Description
RM0453
NRST
pin