STM32 is set as I2C slave

Hardware platform: STM32F401 

Editor: keil 5.18 

Operating system: win7

1. I2C Protocol 

When transmitting data, the SDA line must remain stable during the high level period of the clock. The high or low level state of SDA can only change when the clock signal of the SCL line is low.

Start and Stop Conditions 

　　When the SCL line is high, the SDA line switches from high to low, which indicates the start condition; 

　　When the SCL line is high, the SDA line switches from low to high, which indicates a stop condition.

Addressing mode (7/10-bit address mode)

　　The first 7 bits of the first byte form the slave address, and the least significant bit (LSB) is the 8th bit, which determines the direction of the transmission of the 7-bit address format of the ordinary and repeated start conditions. The least significant bit of the first byte is "0", indicating that the host will write information to the selected slave; "1" indicates that the host will read information from the slave. When an address is sent, each device in the system compares the first 7 bits with its own address after the start condition. If the same, the device will determine that it is addressed by the master. Whether it is a slave receiver or a slave transmitter is determined by the R/W bit.

2. I2C Slave Mode 

1. Set the i2c slave address

I2C_HandleTypeDef I2cHandle;

I2cHandle.Instance = I2C1;

I2cHandle.Init.AddressingMode = I2C_ADDRESSINGMODE_7BIT;

I2cHandle.Init.ClockSpeed ​​= 400000;

I2cHandle.Init.DualAddressMode = I2C_DUALADDRESS_DISABLE;

I2cHandle.Init.DutyCycle = I2C_DUTYCYCLE_16_9;

I2cHandle.Init.GeneralCallMode = I2C_GENERALCALL_DISABLE;

I2cHandle.Init.NoStretchMode = I2C_NOSTRETCH_DISABLE;

I2cHandle.Init.OwnAddress1 = I2C_ADDRESS;

I2cHandle.Init.OwnAddress2 = 0xFE;   

As mentioned above, I2C has two address modes. Here, I2C_ADDRESSINGMODE_7BIT sets I2C to slave address mode 7. OwnAddress1 is the I2C address of this device, that is, the slave address we set ourselves. OwnAddress2 does not need to be set.

2. I2C pin and interrupt initialization

void HAL_I2C_MspInit(I2C_HandleTypeDef *hi2c)

{  

    GPIO_InitTypeDef GPIO_InitStruct;

    /* Enable GPIO TX/RX clock */

    I2Cx_SCL_GPIO_CLK_ENABLE();

    I2Cx_SDA_GPIO_CLK_ENABLE();

    /* Enable I2C1 clock */

    I2Cx_CLK_ENABLE(); 

    /* Configure peripheral GPIO */  

    /* I2C TX GPIO pin configuration */

    GPIO_InitStruct.Pin = I2Cx_SCL_PIN;

    GPIO_InitStruct.Mode = GPIO_MODE_AF_OD;

    GPIO_InitStruct.Pull = GPIO_PULLUP;

    GPIO_InitStruct.Speed ​​= GPIO_SPEED_FAST;

    GPIO_InitStruct.Alternate = I2Cx_SCL_AF;

    HAL_GPIO_Init(I2Cx_SCL_GPIO_PORT, &GPIO_InitStruct);

    /* I2C RX GPIO pin configuration */

    GPIO_InitStruct.Pin = I2Cx_SDA_PIN;

    GPIO_InitStruct.Alternate = I2Cx_SDA_AF;

    HAL_GPIO_Init(I2Cx_SDA_GPIO_PORT, &GPIO_InitStruct);

    /* Configure the NVIC for I2C */   

    /* NVIC for I2C1 */

    HAL_NVIC_SetPriority(I2Cx_ER_IRQn, 0, 2);

    HAL_NVIC_EnableIRQ(I2Cx_ER_IRQn);

    HAL_NVIC_SetPriority(I2Cx_EV_IRQn, 0, 1);

    HAL_NVIC_EnableIRQ(I2Cx_EV_IRQn);

}

3. From sending

uint8_t aTxBuffer[] = "....hello world....";

while (1)

{ 

    if(HAL_I2C_Slave_Transmit_IT(&I2cHandle, (uint8_t*)aTxBuffer, TXBUFFERSIZE+1)!= HAL_OK)

    {

        /* Transfer error in transmission process */

        Error_Handler();    

    }

    HAL_Delay(100);

    while (HAL_I2C_GetState(&I2cHandle) != HAL_I2C_STATE_READY)

    {

        Error_Handler();    

    }

}

That’s it.