An example of microcontroller data communication: analog IIC communication

　　IIC stands for Inter-Integrated Circuit (IC bus). This type of bus was designed by Philips Semiconductor in the early 1980s. It is mainly used to connect integrated circuits (ICS). IIC is a multi-directional control bus, which means that multiple chips can be connected to the same bus structure, and each chip can be used as a control source for real-time data transmission. This method simplifies the signal transmission bus.

　　The I2C serial bus generally has two signal lines, one is the bidirectional data line SDA, and the other is the clock line SCL. All serial data SDA connected to the I2C bus device is connected to the bus SDA, and the clock line SCL of each device is connected to the bus SCL. IO simulation IIC communication is introduced using 51 microcontrollers and AT24C02.

　　Start and stop

 

　　Start condition: must be sent before all commands. While the clock line remains at a high level, the data line level jumps from high to low as the start signal of the IIC bus.

　　Stop condition: while the clock line remains at a high level, the data line level jumps from low to high as the stop signal of the IIC bus. A stop condition must be sent at the end of the operation.

　　void startbit()

　　{

　　clrSCL();

　　setSDA();

　　setSCL(); //When the clock is high

　　clrSDA(); //SDA falling edge

　　clrSCL();

　　}

　　void stopbit()

　　{

　　clrSCL();

　　clrSDA();

　　setSCL(); //When the clock is high

　　setSDA(); //SDA rising edge

　　clrSCL();

　　}

　　Response signal

 

　　After each successful data transmission, the slave device sends an acknowledge signal. When the ninth clock signal is generated, the device that generates the acknowledge signal pulls SDA down to low to notify that 8 bits of data have been received.

　　void respond()

　　{

　　unsigned char i = 0;

　　setSDA(); //Release bus

　　setSCL(); //Clock

　　while(SDA != 0)

　　{

　　i++;

　　if(i > 200) break;

　　}

　　clrSCL();

　　}

　　Read and write byte operations

 

　　The IIC bus protocol is defined as follows:

　　1. Data transmission is allowed only when the bus is not busy. [page]

　　2. During data transmission, when the clock line is high, the data line must be in a fixed state and no jumps are allowed. When the clock line is high, any level change of the data line will be regarded as the start or stop condition of the bus

　　void writeByte(unsigned char dat)

　　{

　　unsigned char i = 0;

　　for(i = 0;i < 8;i++)

　　{

　　clrSCL(); //Pull down the clock line and change the level of the SDA line

　　if(dat & 0x80) setSDA();

　　else clrSDA();

　　setSCL(); //After the SDA level is stable, pull up the clock line

　　dat <<= 1;

　　}

　　clrSCL();

　　}

　　unsigned char readByte()

　　{

　　unsigned char i = 0,tmp = 0;

　　for(i = 0;i < 8;i++)

　　{

　　clrSCL(); //Pull down the clock line

　　tmp <<= 1; //Prepare to read data

　　setSCL(); //Pull up the clock line

　　if(SDA) tmp |= 0x01;

　　}

　　clrSCL();

　　return tmp;

　　}

　　AT24C02 read and write operations

 

　　void writeAT24XX(unsigned char addr,unsigned char dat)

　　{

　　startbit(); //start signal

　　writeByte(0xa0); //device address

　　respond();

　　writeByte(addr); //device internal address

　　respond();

　　writeByte(dat); //data

　　respond();

　　stopbit(); //stop

　　}

 

　　unsigned char readAT24XX(unsigned char addr)

　　{

　　unsigned char dat;

　　startbit(); //start signal

　　writeByte(0xa0); //device address

　　respond();

　　writeByte(addr); //device internal address

　　respond();

　　startbit(); //start signal

　　writeByte(0xa1); //device address

　　respond();

　　dat = readByte(); //data

　　stopbit(); //stop

　　return dat;

　　}

　　The main function content and program running effect:

　　void main()

　　{

　　unsigned char dat;

　　initUart();

　　sendString("UART INIT OK!!! "); //Serial port communication initialization

　　sendString("write 0x05 --> addr 0x00 ");//write 5 to internal address 0

　　writeAT24XX(0x00,0x05); //write data

　　sendString("read dat <-- addr 0x00 "); //read and write data

　　dat = readAT24XX(0x00); //Read data

　　sendString("dat-->"); //Print

　　sendByte(dat + '0');

　　while(1);

　　}