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.

In the associated software, the system clock is set to 48 MHz, an EXTI line is connected to the User push-button thrum PC.13 and configured to generate an interrupt on falling edge. The SysTick is programmed to generate an interrupt each 1 ms and in the SysTick interrupt handler, LED4 is toggled in order to indicate whether the MCU is in Standby or Run mode.

When a falling edge is detected on the EXTI line, an interrupt is generated and the system wake 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 PC.13, 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 LED4 to stop toggling.

Next, the user can wake-up the system in pressing the User push-button which is connected to the wake-up pin PWR_WAKEUP_PIN2. A falling 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 LED4 restarts toggling.

LED4 is used to monitor the system state as follows:

Notes

  1. To measure the current consumption in Standby mode, remove JP6 jumper and connect an amperemeter to JP6 to measure IDD current.

  2. 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.

  3. 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

How to use it ?

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