PWR_STANDBY Example Description

How to enter the Standby mode and wake up from this mode by using an external reset or the WKUP pin.

The SysTick is programmed to generate an interrupt each 1 ms and in the SysTick interrupt handler, LED3 is toggled in order to indicate whether the MCU is in Standby or Run mode.

When a rising edge is detected on wake-up pin PA5(pin13 CN5) the system wakes up the program then checks and clears the standby flag. After clearing the standby flag, the software enables wake-up pin PWR_WAKEUP_PIN2 connected to PA5(pin13 CN5), then the corresponding flag indicating that a wakeup event was received from the PWR_WAKEUP_PIN2 is cleared. Finally, the system enters again Standby mode causing LED3 to stop toggling.

Next, the user can wake-up the system by applying a high level to the wake-up pin PWR_WAKEUP_PIN2. A rising edge on WKUP pin will wake-up the system from Standby. Alternatively, an external RESET of the board will lead to a system wake-up as well.

After wake-up from Standby mode, program execution restarts in the same way as after a RESET and LED3 restarts toggling.

LED3 is used to monitor the system state as follows:

Notes

  1. Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds) based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower) than the peripheral interrupt. Otherwise the caller ISR process will be blocked. To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.

  2. The application needs to ensure that the SysTick time base is always set to 1 millisecond to have correct HAL operation.

Keywords

Power, PWR, Standby mode, Interrupt, EXTI, Wakeup, Low Power, External reset

Directory contents

Hardware and Software environment

@par How to use it ?

In order to make the program work, you must do the following :