I2C communication between 2 STM32 MCUs

[RSy.1]

Hello I am trying to learn I2C communication between 2 STM32F103C8 MCUs. MCU1 acts as the master and MCU2 acts as the slave. I am using CubeMX to configure the settings however I could not establish a link between the 2 MCUs. What I wanted to happen is that once I toggle a button connected to MCU1, the LED controlled by MCU2 should be enabled.

May I ask for your advice on the code below.

Master MCU1 code:
     
   //Enable Button_LED1 and transmit 0xFF data.  0x5A (0b01011010) Slave + Write (0)
        if(HAL_GPIO_ReadPin(BUTTON_LED1_GPIO_Port, BUTTON_LED1_Pin))
        {
            Buffer_I2C[0] = 0xFF;
            HAL_I2C_Master_Transmit(&hi2c1, 0x5A, Buffer_I2C, 1, 10);
        }
 
        //Disable Button_LED1 and transmit 0x00 data
        else
        {
            Buffer_I2C[0] = 0x00;
            HAL_I2C_Master_Transmit(&hi2c1, 0x5A, Buffer_I2C, 1, 10);
        } 
 
 
Slave MCU2 code:
 
  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed = 100000;
  hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1 = 0x5B;                                                      //Slave + Read (1)
  hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2 = 0;
  hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
  if (HAL_I2C_Init(&hi2c1) != HAL_OK)
 
    {           
        HAL_I2C_Slave_Receive(&hi2c1, Buffer_I2C, 1, 10);
        uint8_t data = Buffer_I2C[0];
        switch(data)
        {
            case 0xFF:
            HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_SET);
            break;
            
            case 0x00:
            HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_RESET);
            break;
            
            default:
            break;
        }
    }

:

[KnarfB]

The timeout for HAL_I2C_Slave_Receive is pretty short. Try with a longer timeout, even HAL_MAX_DELAY for a blocking read. And: check the return code.

[RSy.1]

Thank you for the hint. I tried changing the timeout longer to 50 but still it is not working. What is wrong with the return code?

[Msd.1]

Is this your actual code?

if yes in you slave code your if statement should be

if (HAL_I2C_Init(&hi2c1) == HAL_OK)

[RSy.1]

Sorry I forgot to tell that the If statement of the Slave is in the while(1) loop.

I did not change the line you mentioned as this was generated by CubeMX:

if (HAL_I2C_Init(&hi2c1) != HAL_OK)

Slave MCU2 code:
 
  hi2c1.Instance = I2C1;
  hi2c1.Init.ClockSpeed = 100000;
  hi2c1.Init.DutyCycle = I2C_DUTYCYCLE_2;
  hi2c1.Init.OwnAddress1 = 0x5B;                                                      //Slave + Read (1)
  hi2c1.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;
  hi2c1.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;
  hi2c1.Init.OwnAddress2 = 0;
  hi2c1.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;
  hi2c1.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;
  if (HAL_I2C_Init(&hi2c1) != HAL_OK)
 
 
  while(1)
    {           
        HAL_I2C_Slave_Receive(&hi2c1, Buffer_I2C, 1, 10);
        uint8_t data = Buffer_I2C[0];
        switch(data)
        {
            case 0xFF:
            HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_SET);
            break;
            
            case 0x00:
            HAL_GPIO_WritePin(LED2_GPIO_Port, LED2_Pin, GPIO_PIN_RESET);
            break;
            
            default:
            break;
        }
    }
}

[KnarfB]

You don't check it.

[RSy.1]

I tried changing that line as you suggested but still not working.

[TDK]

> as this was generated by CubeMX:

Are you sure you didn't delete a call to Error_Handler? The code you posted looks edited from what CubeMX generates.

> HAL_I2C_Slave_Receive(&hi2c1, Buffer_I2C, 1, 10);

You should be looking at the return value and only processing the byte if it was actually received, as opposed to a timeout happening.

[RSy.1]

No I did not edit anything else after I generated the code only the address of the slave. Thanks for the suggestions.

[RShan.3]

In master , you mentioned the slave address as 0x5A " HAL_I2C_Master_Transmit(&hi2c1, 0x5A, Buffer_I2C, 1, 10); "

In Slave , you mentioned the slave address as 0x5B " hi2c1.Init.OwnAddress1 = 0x5B; "

Actually, API will call 7-bit address and based on the Transmit & Receive functions, it will automatically append the R/nW bit. Yes, API "ll do it for you.

Just declare the " 7-bit address with right shift of 1 bit " throughout the program.