Table 27. Stop Mode Entry And Exit (For Stm32F405Xx/07Xx And Stm32F415Xx/17Xx) - STMicroelectronics STM32F405 Reference Manual

Power controller (PWR)
Note: If the application needs to disable the external clock before entering Stop mode, the HSEON
bit must first be disabled and the system clock switched to HSI.
Otherwise, if the HSEON bit is kept enabled while the external clock (external oscillator) can
be removed before entering stop mode, the clock security system (CSS) feature must be
enabled to detect any external oscillator failure and avoid a malfunction behavior when
entering stop mode.
Exiting Stop mode (for STM32F405xx/07xx and STM32F415xx/17xx)
The Stop mode is exited according to
Refer to
When exiting Stop mode by issuing an interrupt or a wakeup event, the HSI RC oscillator is
selected as system clock.
When the voltage regulator operates in low-power mode, an additional startup delay is
incurred when waking up from Stop mode. By keeping the internal regulator ON during Stop
mode, the consumption is higher although the startup time is reduced.

Table 27. Stop mode entry and exit (for STM32F405xx/07xx and STM32F415xx/17xx)

Stop mode
Mode entry
132/1731
Table 27 for more details on how to exit Stop mode.
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– No interrupt (for WFI) or event (for WFE) is pending,
– SLEEPDEEP bit is set in Cortex
– PDDS bit is cleared in Power Control register (PWR_CR),
– Select the voltage regulator mode by configuring LPDS bit in PWR_CR.
On Return from ISR:
– No interrupt is pending,
– SLEEPDEEP bit is set in Cortex
– SLEEPONEXIT = 1,
– PDDS bit is cleared in Power Control register (PWR_CR).
Note: To enter Stop mode, all EXTI Line pending bits (in
(EXTI_PR)), all peripheral interrupts pending bits, the RTC Alarm
(Alarm A and Alarm B), RTC wakeup, RTC tamper, and RTC time
stamp flags, must be reset. Otherwise, the Stop mode entry
procedure is ignored and program execution continues.
DocID018909 Rev 11
Section : Exiting low-power
Description
®
-M4 with FPU System Control register,
®
-M4 with FPU System Control register,
RM0090
mode.
Pending register