Why I2C pins are always low in STM32F0?

[MSalv.1]

Hello, I have a SMT32F042, i'm trying to use I2C. I used STM32 CubeMX to generale a new blank project with only i2c (see attached). I2C on non standard pins. The problem is that they always stay low, it does not transfer anything.

This is what I captured with the logic analyzer, after starting the debug, it goes low.

I attach the code, but it is really standard: https://pastebin.com/ijX9RLEG

I tried also to configure everything as output pin with external pull up (9,5k) and open drain... it works, so my pull up resistor are working.

I really don't know what to check next. THe same come with nucleo works perfectly.

Thank you,

UPDATE 1:

I tried with i2c1 normal pins (PF0 and PF1), and it worked. For my configuration (PB14+PB13) the result is still the same. I ended up that maybe is a but in stm32cube with setting alternate function. Anybody can see something strange?

In addition with main.c code, I am posting here the hal_msp.c code involved:

/**
* @brief I2C MSP Initialization
* This function configures the hardware resources used in this example
* @param hi2c: I2C handle pointer
* @retval None
*/
void HAL_I2C_MspInit(I2C_HandleTypeDef* hi2c)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  if(hi2c->Instance==I2C1)
  {
  /* USER CODE BEGIN I2C1_MspInit 0 */
 
  /* USER CODE END I2C1_MspInit 0 */
  
    __HAL_RCC_GPIOB_CLK_ENABLE();
    /**I2C1 GPIO Configuration    
    PB13     ------> I2C1_SCL
    PB14     ------> I2C1_SDA 
    */
    GPIO_InitStruct.Pin = GPIO_PIN_13|GPIO_PIN_14;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
    GPIO_InitStruct.Pull = GPIO_PULLUP;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;
    HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
 
    /* Peripheral clock enable */
    __HAL_RCC_I2C1_CLK_ENABLE();
  /* USER CODE BEGIN I2C1_MspInit 1 */
 
  /* USER CODE END I2C1_MspInit 1 */
  }
 
}

[lbthomsen]

I2C pins are generally - as you point out yourself - configured as open drain, so they don't normally pull the pin high actively. It _is_ possible to use the internal pull up resistor, but those are in the 50 k range, which would be considered a "weak pull up". It will "probably" work if the transmission lines are short, but in general I2C should be pulled high more aggressively (10k or even lower).

[KnarfB]

If you have configured a pin as I2C, the HAL_GPIO_WritePin functions do not have an effect anymore. The pin is either GPIO or alternate function (like I2C) or else.

hth

KnarfB

[MM..1]

Check is interrupt for I2C peripheral enabled and ofcourse all pin Vdd and Vss is OK.

[MSalv.1]

Hello, sorry, I was not clear. In another try and another code, I tried to reconfigure everything as GPIO and I tried WritePin to assure that the pin was not broken and the external pull up was working correctly. And it was working as expected, so I excluded the pullup damage/pin damage/connection issues.

[MSalv.1]

Hello, thank you for your answer. I have a 9,5k pullup resistor. I tried (in a parallet attempt) configuring the pins as GPIO (open drain), and it correctly worked, so I have excluded the pullup damage/pin damage/connection issues.

[MSalv.1]

I am starting to try in blocking mode, using HAL_I2C_Master_Transmit, but HAL_I2C_Master_Transmit_IT does nothing as well. Vdd and Vss are connected correctly

[MSalv.1]

FOUND! As expected, was a stm32cubemx bug. It did everything for setting up the i2c but did not enable the alternate function registry.

It started working with:

GPIO_InitStruct.Alternate = ((uint8_t)0x05U);

inside hal_msc.c.

[OTedd.1]

I had the same problem on the Nucleo F767Zi board using STM32CubeIDE:

Version: 1.12.0

Build: 14980_20230301_1550 (UTC)

when trying to get the I2C lines to work.

Adding these lines (manually) worked:

#define 	GPIO_AF4_I2C1   ((uint8_t)0x04) /* I2C1 Alternate Function mapping */
#define 	GPIO_AF4_I2C2   ((uint8_t)0x04) /* I2C2 Alternate Function mapping */
#define 	GPIO_AF4_I2C3   ((uint8_t)0x04) /* I2C3 Alternate Function mapping */
  /*Configure I2C1_SDA_Pin pin : I2C1_SDA_Pin */
  GPIO_InitStruct.Pin = I2C1_SDA_Pin;
  GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
  GPIO_InitStruct.Pull = GPIO_PULLUP;
  GPIO_InitStruct.Alternate = GPIO_AF4_I2C1;
  HAL_GPIO_Init(I2C1_SDA_GPIO_Port, &GPIO_InitStruct);
 
  /*Configure I2C1_SCL_Pin pin : I2C1_SCL_Pin */
	GPIO_InitStruct.Pin = I2C1_SCL_Pin;
	GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;
	GPIO_InitStruct.Pull = GPIO_PULLUP;
	GPIO_InitStruct.Alternate = GPIO_AF4_I2C1;
	HAL_GPIO_Init(I2C1_SCL_GPIO_Port, &GPIO_InitStruct);
/* USER CODE END MX_GPIO_Init_2 */