PA9 is high voltage level when configured as input pull-down mode

[liliangbao]

Hello, everyone.

    I use STM32L496 on my board, and use PA9 as a GPIO for input, without any external resister.

    Software program is based on HAL. I have a sample demo like this:

    int main(void)
    {
        HAL_Init();
        BSP_Init();

        while(1)
        {
            delay_ms(1000);
        }
    }

    While, in the BSP_Init(), like this:

    void BSP_Init(void)
    {
        GPIO_InitTypeDef GPIO_InitStruct = {0};

        __HAL_RCC_GPIOA_CLK_ENABLE();

        GPIO_InitStruct.Pin       = GPIO_PIN_9 | GPIO_PIN_10 | GPIO_PIN_11
        GPIO_InitStruct.Mode   = GPIO_MODE_INPUT;
        GPIO_InitStruct.Pull      = GPIO_NOPULL;     // or GPIO_PULLDOWN
        GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
        HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    }

    But, on the board, I measured PA9 has a high voltage level, but PA10 and PA11 is low. If do not call BSP_Init(), PA9 is high level,too. If a change GPIO_InitStruct.Pull to GPIO_PULLDOWN, the result is same as above. I checked the register, three pin has the same configure. And no other place configure these pin.

    Is there same mistake about my use? It's been bothering me for a long time. Does anyone provide any help, Thanks very much!

[SofLit]

Hello, 

In your schematics there is the signal called "U1 TX2". What kind of signal is this: input or output? The voltage you are measuring could be sourced by this signal.

Could you please share the schematics?

[Michal Dudka · Accepted solution]

A) Show us all relevant schematic (U1 TX2)
B) Check PCB trace from shortcut to VCC
C) Explain how exactly did you measured "high level" on pin without pullup/down. It is little bit tricky to measure floating input !

[liliangbao]

Thank you for reply.  "U1 TX2" is input, and it connect nothing. I will check carefully.

[liliangbao]

Thank you for reply.  I will check carefully according to your recommendation.