how keep GPIO Output in StandByMode under minus 12 degrees Celsius with STM32F091VCT7

[DPark.2]

set GPIO Output as pull down on STM32CubeMX.

HAL_GPIO_Write( Module_PWR_CTR_Port1, Module_PWR_CTR_Pin, RESET );
HAL_GPIO_Write( Module_PWR_CTR_Port2, Module_PWR_CTR_Pin, RESET );
HAL_GPIO_Write( Module_PWR_CTR_Port3, Module_PWR_CTR_Pin, RESET );
 
__HAL_PWR_CLEAR_FLAG(PWR_FLAG_WU);
HAL_PWR_EnterSTANDBYMode();

when Room temperature, even in STANDBYMode keep GPIO Output Low, but operation in minus 12 degrees Celsius, gpio output level was 1.2V ~ 1.8V. and if come back to room temperature, gpio output level was 0.2V.

I am asking if I am setting something wrong, or if it is difficult to maintain the output in StandByMode.

[berendi · Accepted solution]

The description of standby mode in the reference manual states that the contents of hardware registers are not preserved except RTC and IWDG.

Use stop mode instead, or external pulldown resistors.

[DPark.2]

In the end, as you said, I added an external pull-down resistor to the power control pin.

In general, I know that a pull-up resistor is configured for response speed in communication, but is it a stupid idea to attach it to a UART pin at BaudRate 115200 speed to reduce current consumption?