Why is my PIN configured as Input, but still acts as Output?

[Dali]

Hi all

I'm working on Nucleo-F410RB

I have a UV filter that sends back a 0V-5V digital signal that I'm trying to read on PIN D13 (PA5).

The issue if the following (I'm using a multimeter to read the voltage, and all components have a common ground):

• when the cable is not connected to the PIN
  • I read a voltage of 5V from the UV filter side
  • I read a voltage of 1.7V from the PIN D13 side
• when I connect them both
  • I read a voltage of 2V

Even though I can interpret the signal, the imposed voltage on the UV filter makes him go into default mode.

 

Here is the code I'm using

#define OTH2_GPIO GPIOA

#define OTH2_PIN GPIO_PIN_5

  /*Configure GPIO pin Output Level */

  HAL_GPIO_WritePin(GPIOB, GPIO_PIN_0|GPIO_PIN_3|GPIO_PIN_4|GPIO_PIN_6|GPIO_PIN_5|GPIO_PIN_10, GPIO_PIN_RESET);

  HAL_GPIO_WritePin(OTH1_GPIO, OTH1_PIN, GPIO_PIN_RESET);

  HAL_GPIO_WritePin(OTH2_GPIO, OTH2_PIN, GPIO_PIN_RESET);

  GPIO_InitStruct.Pin = OTH2_PIN;

  GPIO_InitStruct.Mode = GPIO_MODE_INPUT;

  GPIO_InitStruct.Pull = GPIO_NOPULL;

  HAL_GPIO_Init(OTH2_GPIO, &GPIO_InitStruct);

[gbm]

PA5 (Arduino D13) pin is connected to an LED ("user LED") - check the Nucleo schematic.

[S.Ma]

And remember that analog inputs on some STM32 are 3.3V tolerant only, so don't connect a 5V signal to it, unless you made sure reading the datasheet that this is safe to do so.