Microcontroller: IIC bus communication

1. IIC bus communication

1 Introduction:

 IIC stands for Inter-Integrated Circuit (Integrated Circuit Bus). The I2C bus is a serial bus introduced by PHLIPS. The I2C bus has only two bidirectional signal lines. One is the data line SDA and the other is the clock line SCL .

 Each device connected to the I2C bus has a unique address . The data transfer between the host and other devices can be sent by the host to other devices, then the host is the transmitter. A device that receives data on the bus is a receiver.

2. Commonly used serial expansion buses are:

(1), I2C (Inter IC BUS) bus
(2), single bus (1-WIRE BUS)
(3), SPI (Serial Peripheral Interface) bus, etc.

3. IIC bus circuit connection

 The I2C bus is connected to the positive power supply through a pull-up resistor. When the bus is idle, both lines are high.

        

4. IIC bus communication protocol

(1) Start and end signals

 During the period when the SCL line is at a high level, the change of the SDA line from a high level to a low level indicates the start signal;

 During the period when the SCL line is at a high level, the change of the SDA line from a low level to a high level indicates a termination signal.

(2) Answer and non-response

 The IIC bus protocol stipulates that after each byte of data is transmitted, there must be a response signal to determine whether the data transmission is received by the other party. The response signal is generated by the receiving device . During the period when SCL is at a high level, the receiving device pulls SDA low to a low level, indicating that the data transmission is correct and a response is generated.

(3) Data transmission

Data Bit Validity Regulations

 When the I2C bus is transmitting data , the data on the data line must remain stable during the period when the clock signal is at a high level. Changes are allowed .

5. Basic functions of IIC communication

(1) Start and stop signal

 

i2c_Start()

 {

    SDA = 1;   //SCL为高电平时，SDA 出现一个下跳沿表示I2C总线启动
    SCL = 1;
    i2c_Delay();
    SDA = 0;
    i2c_Delay();

    SCL = 0;  // 启动后将SCL点平拉低
    i2c_Delay();
 }

(2) Termination signal

void i2c_Stop()
{
    SDA = 0;  //当SC高电平时，SDA出现一个上升沿表示I2C总线停止
    SCL = 1;
    i2c_Delay();
    SDA = 1;
    i2c_Delay(); 
}

(3) Send data

void i2c_SendByte(unsigned char Byte)
{
    unsigned char i = 0;   
    for (i = 0; i < 8; i++)  
    {
        if(Byte & 0x80)    //IIC规定下发送高位数据
        {
             SDA = 1;  
        }
        else   
             SDA = 0;  
        SCL = 1;          //在SCL为高电平期间写入数据
        i2c_Delay();   
        SCL = 0;  
        Byte <<= 1;
        if (i == 7)
            SDA = 1;      //在发送完数据后将SDA拉高
        i2c_Delay();
    }
}

(4) Receive data

unsigned char i2c_ReadByte()
{
    unsigned char i = 0;
    unsigned char value = 0;
    for (i = 0; i < 8; i++)
    {
         value <<= 1;      //先读取高位
         SCL = 1;          //SCL 为高电平时读取数据
         i2c_Delay(); 
         if(SDA)
         {
             value++;
         }
         SCL = 0;
         i2c_Delay();
    }
    return value;
}

(5) Send a response signal

void char i2c_Ack()
{
    SDA = 0;      //SCL为高电平时间SDA拉低表示应答
    i2c_Delay();
    SCL = 1;
    i2c_Delay();
    SCL = 0;
    i2c_Delay();
    SDA = 1;
    i2c_Delay();
}

(6) Send a non-response signal

void i2c_NAck()
{
    SDA = 1;    //SCL高电平期间SDA拉高表示非应答
    i2c_Delay();
    SCL  = 1;
    i2c_Delay();
    SCL = 0;
    i2c_Delay();
}

(7) Waiting for a response

unsigned  char i2c_WaitAck()
{
    unsigned char ret;
    SDA = 1;      
    i2c_Delay();
    SCL = 1;       //把SCL拉高读取SDA的点平高低，低电平表示应答

    i2c_Delay();
    if(SDA == 1)
    {
        ret = 1;
    }
    else
        ret = 0;
    SCL = 0;
    i2c_Delay();
    return ret;
}

(8) Check the IIC device bus

unsigned char i2c_CheckDevice(unsigned char _Address)
{
    unsigned char UcAck;
    if (SDA == 1 &&  SCL == 1)
    {
        i2c_Start();
        i2c_SendByte(_Address|I2C_WR); //发送地址
        ucAck = i2c_WaitAck();         //等待接收应答    
        i2c_Stop();                    //停止信号
        return ucAck;                  
    }
    return 1;
}