简单的I2C总线传输例子

说明：进行I2C传输，时候在读和写时1个字节需要start write/read stop

start在保持SCL为高，变化SDA为低

stop相反。

在write时，先置SCL为0，然后变化sda然后置SCL为1，另外一端感知到电压变化即存了1bit，连续传8位。

在read时，先设置为读操作，然后将SCL置为0，读取1个bit，然后将SCL置1，对方发送第2bit，如此连续8位。

#include <REG52.h>
#include <intrins.h>

#define uchar unsigned char
#define uint  unsigned int

sbit scl=P1^5;  //24c08 SCL
sbit sda=P3^6;  //24c08 SDA

uchar code table[10] = {0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f};
uchar sec;      //定义计数值，每过1秒，sec加1
uint write;        //写标志位
void flash(void)
{
    _nop_();
    _nop_();
}//延迟2us

void x24c02_init(void)
{
    scl = 1;
    flash();
    sda = 1;
    flash();
}

void start(void)
{
    scl = 1;
    flash();
    sda = 1;
    flash();
    sda = 0;
    flash();
    scl = 0;
    flash();
}

void stop()
{
    scl = 0;
    flash();
    sda = 0;
    flash();
    scl = 1;
    flash();
    sda = 1;
    flash();
}

void writex(uchar j)
{
    uchar i,temp;
    temp = j;
    for(i=0; i<8; i++)
    {
        scl = 0;
        flash();
        sda = (bit)(temp & 0x80);
        flash();
        scl = 1;
        flash();
        temp = temp << 1;
    }
    scl = 0;
    flash();
}

uchar readx(void)
{
    uchar i, j, k = 0;
    for(i=0; i<8; i++)
    {
        scl = 0;
        flash();
        if(sda == 1)
        {
            j = 1;
        }
        else j = 0;
        k = (k << 1) | j;
        scl = 1;
        flash();
    }
    return(k);
}

void ack(void)
{
    uchar i = 0;
    scl = 1;
    flash();
    while((sda == 1) && (i < 255))//保持scl高电平，等待如果高电平一直等，知道sda低电平或超时
    {
        i++;
    }
    scl = 0;
    flash();
}

uchar x24c02_read(uchar address)//先写从设备地址，然后写读写byte地址
{
    uchar i;
    start();
    writex(0xa0);
    ack();
    writex(address);
    ack();
    start();
    writex(0xa1);
    ack();
    i = readx();
    stop();
    return(i);
}

void x24c02_write(uchar address, uchar info)
{
    start();
    writex(0xa0);
    ack();
    writex(address);
    ack();
    writex(info);
    ack();
    stop();
}
void Delay_1ms(uint i)
{
    uchar x, j;
    for(j=0; j<i; j++)
    for(x=0; x<=148; x++)
    ;
}

void LED()                  //LED显示函数
{
    P2 = 6;
    P0 = table[sec / 10];
    Delay_1ms(5);
    P2 = 7;
    P0 = table[sec % 10];
    Delay_1ms(5);
}
void time0(void) interrupt 1 using 3  //定时中断服务函数
{
    static uchar Count = 0;
    TH0 = 0x4c; //对TH0 TL0赋值
    TL0 = 0x00; //重装计数初值
    Count++;
    if(Count == 20)  //计满20次（1秒）时
    {
        Count = 0;   //重新再计
        sec++;
        write = 1;   //1秒写一次24C08
        if(sec == 100) //定时100秒，在从零开始计时
        {
            sec = 0;
        }
    }
}

void Time0_Init(void)
{
    TMOD = 0x01;              //定时器工作在方式1
    ET0 = 1;
    EA = 1;
    TH0 = 0x4c;     //对TH0 TL0赋值
    TL0 = 0x00;     //使定时器0.05秒中断一次
    TR0 = 1;                           //开始计时
}

void Main(void)
{
    x24c02_init();            //初始化24C02
    sec = x24c02_read(2);    //读出保存的数据赋于sec
    Time0_Init();
    while(1)
    {
         LED();
        if(write == 1)                //判断计时器是否计时一秒
        {
            write =0;              //清零
            x24c02_write(2,sec);   //在24c08的地址2中写入数据sec
        }
    }
}