[stm32u585] Voltage drops on GPIO when wakes up from standby

[lll]

hello

Description:

I'm currently working with the STM32U585 and encountered an issue related to GPIO behavior after waking up from standby mode.

Before entering standby, I configure certain GPIO pull-up:(No external pull-down resistors on the affected pins)

HAL_PWREx_EnableGPIOPullUp(PWR_GPIO_D, PWR_GPIO_BIT_14);
HAL_PWREx_EnablePullUpPullDownConfig();

However, after the MCU wakes up from standby (via wakeup pin), I observe a brief voltage drop on those previously GPIOs, about 300ms. This drop occurs before the firmware reinitializes the GPIO configuration:

i added a delay(implemented with i--)before calling the HAL_Init() function, and the voltage drop became less pronounced:

Questions:

1. Is this behavior expected due to the standby mode reset mechanism?

2. Is there a recommended way to retain GPIO output levels across standby wakeup?

3. Could this be related to the IO pull settings or the boot configuration?

4. Are there any hardware-level workarounds to avoid this voltage dip?

5. Why does delay have such an impact

[lll]

It seems that the pull-up did not take effect

[Saket_Om]

Hello @lll 

Is the pin PD14 is disconnected from other device when measuring the voltage level?

[lll]

Yes, PD14 is disconnected from other device, and I tested two IO ports both exhibited the same phenomenon

[TDK]

Doesn't make a whole lot of sense to me.

If you set the pulldown resistor instead of pullup, what happens?

Is PD14 being initialized as output? Initialize it as input instead, with a pullup. What happens?

 

300ms is an eternity. Why does it take so long to re-initialize the pin?