DocID024597 Rev 5 175/1830
RM0351 Power control (PWR)
198
When exiting Stop 2 mode by issuing an interrupt or a wakeup event, the HSI16 oscillator is
selected as system clock if the bit STOPWUCK is set in Clock configuration register
(RCC_CFGR). The MSI oscillator is selected as system clock if the bit STOPWUCK is
cleared. The wakeup time is shorter when HSI16 is selected as wakeup system clock. The
MSI selection allows wakeup at higher frequency, up to 48 MHz.
When exiting the Stop 2 mode, the MCU is in Run mode (Range 1 or Range 2 depending on
VOS bit in PWR_CR1).
5.3.9 Standby mode
The Standby mode allows to achieve the lowest power consumption with BOR. It is based
on the Cortex
®
-M4 deepsleep mode, with the voltage regulators disabled (except when
SRAM2 content is preserved). The PLL, the HSI16, the MSI and the HSE oscillators are
also switched off.
Table 29. Stop 2 mode
Stop 2 mode Description
Mode entry
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– SLEEPDEEP bit is set in Cortex
®
-M4 System Control register
– No interrupt (for WFI) or event (for WFE) is pending
– LPMS = “010” in PWR_CR1
On return from ISR while:
– SLEEPDEEP bit is set in Cortex
®
-M4 System Control register
– SLEEPONEXIT = 1
– No interrupt is pending
– LPMS = “010” in PWR_CR1
Note: To enter Stop 2 mode, all EXTI Line pending bits (in Pending
register 1 (EXTI_PR1)), and the peripheral flags generating wakeup
interrupts must be cleared. Otherwise, the Stop mode entry
procedure is ignored and program execution continues.
Mode exit
If WFI or Return from ISR was used for entry:
Any EXTI Line configured in Interrupt mode (the corresponding EXTI
Interrupt vector must be enabled in the NVIC). The interrupt source can
be external interrupts or peripherals with wakeup capability. Refer to
Table 57: STM32L4x5/STM32L4x6 vector table.
If WFE was used for entry and SEVONPEND = 0:
Any EXTI Line configured in event mode. Refer to Section 14.3.2:
Wakeup event management.
If WFE was used for entry and SEVONPEND = 1:
Any EXTI Line configured in Interrupt mode (even if the corresponding
EXTI Interrupt vector is disabled in the NVIC). The interrupt source can
be external interrupts or peripherals with wakeup capability. Refer to
Table 57: STM32L4x5/STM32L4x6 vector table.
Any EXTI Line configured in event mode. Refer to Section 14.3.2:
Wakeup event management.
Wakeup latency
Longest wakeup time between: MSI or HSI16 wakeup time and regulator
wakeup time from Low-power mode + Flash wakeup time from Stop 2
mode.
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