Power controller (PWR) RM0390
106/1328 RM0390 Rev 4
5.3.6 Standby mode
The Standby mode allows to achieve the lowest power consumption. It is based on the
Cortex
®
-M4 with FPU deepsleep mode, with the voltage regulator disabled. The 1.2 V
domain is consequently powered off. The PLLs, the HSI oscillator and the HSE oscillator are
also switched off. SRAM and register contents are lost except for registers in the backup
domain (RTC registers, RTC backup register and backup SRAM), and Standby circuitry (see
Figure 8).
Entering Standby mode
The Standby mode is entered according to Entering low power mode, when the
SLEEPDEEP bit in the Cortex
®
-M4 with FPU System Control register is set.
Table 18. Stop mode entry and exit for STM32F446xx
Stop mode Description
Mode entry
WFI (Wait for Interrupt) or WFE (Wait for Event) while:
– Set SLEEPDEEP bit in Cortex
®
-M4 with FPU System Control register
– Clear PDDS bit in Power Control register (PWR_CR)
– Select the voltage regulator mode by configuring LPDS, MRUDS, LPUDS and
UDEN bits in PWR_CR (see Table 17: Stop operating modes).
On Return from ISR while:
– SLEEPDEEP bit is set in Cortex
®
-M4 with FPU System Control register
– SLEEPONEXIT = 1
– LPMS = “000” in PWR_C1: volatage regulator in main regulator mode
– LPMS = “001” in PWR_C1: volatage regulator in low power regulator mode
Note: To enter the Stop mode, all EXTI Line pending bits in Pending register
(EXTI_PR), all peripheral interrupts pending bits, the RTC Alarms (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.
Mode exit
If WFI or Return from ISTR was used for entry:
All EXTI lines configured in Interrupt mode (the corresponding EXTI Interrupt
vector must be enabled in the NVIC). Refer to Table 38: Vector table for
STM32F446xx.
If WFE was used for entry and SEVONPEND = 0:
All EXTI Lines configured in event mode. Refer to Section 10.2.3: 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 38: Vector
table for STM32F446xx.
Wakeup event: refer to Section 10.2.3: Wakeup event management
Wakeup latency Refer to Table 17: Stop operating modes
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