51单片机之I^2C总线

    I^2C总线的SDA与CLK都是线与关系.
为了避免混乱I^2C总线要通过总线仲裁决定总线由哪一台主机控制
I^2C总线的数据位的有效性:时钟信号为高电平期间
     数据线上的数据必须保持稳定,只有在时钟信号为低电平时,
   数据线上的数据才可以变化.
图片
I^2C总线的起始信号与终止信号,每一字节必须是8位长度
   发完还有一位应答位,所以一共会有9位.
    在编写程序时,只要严格按照时序图来,万事OK,下面是我写的一示例程序,功能是先向2402芯片写入一字节数据,然后再将其读出,显示到数码管

#include <reg52.h>
#define uint unsigned int
#define uchar unsigned char

sbit scl = P1^6;
sbit sda = P1^7;
uchar code table[]={0x7e,0x0c,0xb6,0x9e,0xcc,0xda,0xfa,0x0e,0xfe,0xde};
sbit sda0 = P1^0;
sbit clk = P1^1;
sbit dig1 = P1^2;
sbit dig2 = P1^3;
sbit dig3 = P1^4;
sbit dig4 = P1^ 5;
void delay(uint);
/** 初始化IIC,将i^2C总线的电平拉高 **/
void init()
{
	sda = 1;
	scl = 1;
	delay(1);
}
/** 向IIC写入一个字节 **/
void write_byte(uchar b)
{
	uchar i,temp;
	temp = b;
	scl = 0;
	for(i=0;i<8;i++)
    {
		temp <<= 1;
		sda = CY;
		delay(1);
		scl = 1;
		delay(1);
		scl = 0;
	}
	delay(1);
	scl = 0;
	sda = 1;
}
/** 从IIC读出一字节数据 **/
uchar read_byte()
{
	uchar i,temp;
	scl = 0;
	sda = 1;
	delay(1);
	for(i=0;i<8;i++)
	{
		delay(1);
		temp <<= 1;
		scl = 1;
		delay(1);
		temp |= sda;
		delay(1);
		scl = 0;
	}
	delay(1);
	scl = 0;
	sda = 1;
	return temp;
}
/** IIC的开始信号 **/
void start()
{
	sda = 1;
	delay(1);
	scl = 1;
	delay(1);
	sda = 0;
	delay(1);
	sda = 1;
	scl = 0;	
}
/** IIC的停止信号 **/
void stop()
{
	sda = 0;
	delay(1);
	scl = 1;
	delay(1);
	sda = 1;
	scl = 0;
	delay(1);
}
/** IIC的应答函数 **/
void response()
{
	uchar temp = 0;
	sda = 1;
	scl = 0;
	delay(1);
	while(sda && temp<250)
		temp ++;
	scl = 1;
	delay(1);
	scl = 0;
	delay(1);
	sda = 1;
}
//延迟函数
void delay(uint u)
{
	uint x,y;
	for(x=u;x>0;x--)
		for(y=110;y>0;y--);
}
/** 向数据码管写入一个字节数据 **/
void write(uchar u)
{
    uchar i;
	for(i=0;i<8;i++)
	{
		clk = 1;
		sda0 = u&0x80;
		clk = 0;
		u = u<<1;	
	}
}
/** 显示一个3位的整数 **/
void display(uchar num)
{
	uchar bai,shi,ge;
	bai = num/100;
	shi = num%100/10;
	ge = num%10;
	/* 显示个位 */
	dig4 = 0;
	write(table[ge]);
	delay(10);
	dig4 = 1;
	/* 显示十位 */
	dig3 = 0;
	write(table[shi]);
	delay(10);
	dig3 = 1;
	/* 显示百位 */
	dig2 = 0;
	write(table[bai]);
	delay(10);
	dig2 = 1;

}
/** 向2402芯片指定地址写入一字节数据 **/
void write2402(uchar add,uchar u)
{
	start();
	write_byte(0xa0);
	response();
	write_byte(add);
	response();
	write_byte(u);
	response();
	stop();
}
/** 从2402芯片指定地址读出一字节数据 **/
uchar read2402(uchar add)
{
	uchar result;
	start();
	write_byte(0xa0);
	response();
	write_byte(add);
	response();
	start();
	write_byte(0xa1);
	response();
	result = read_byte();
	stop();
	return result;
}
void main()
{
	uchar result;
	init();
	write2402(5,159);
	delay(20);
	result = read2402(5);
	while(1)
		display(result);
}

附上一份2402文档,以后可参考