本人小白一枚，在此记录STC89C51单片机与AT24C02通过IIC方式通讯。

用到的IIC非高速，采用5us延时；emm...主要细节在读取从机应答，以及发送完数据需要拉低时钟线SCL，拉高数据线SDA以允许AT24C02来产生应答信号。详细见注释

#ifndef IIC
#define IIC

#include "reg52.h"

void Delay5us();
void START();
void STOP();
void READ_ACK();
void SEND_ACK(bit i);
void SEND_DATA(unsigned char Data);
unsigned char READ_DATA();
void AT24C02_WRITE(unsigned char Addr,unsigned char Data);
unsigned char AT24C02_READ(unsigned char Addr);

#endif

#include "iic.h"

sbit SCL = P2^1;
sbit SDA = P2^0;

void Delay5us()		//@11.0592MHz
{
}

void START()      //起始信号
{
    SCL = 1;
	SDA = 1;
	Delay5us();
	SDA = 0;
	Delay5us();
}

void STOP()       //停止信号
{
	/*****/
	//避免停止信号前面的起始信号
    SCL = 0; 
	SDA = 0;
	/*****/
	SCL = 1;
	Delay5us();
	SDA = 1;
	Delay5us();
}

void READ_ACK()   //读从机应答
{
    SCL = 1;   //读取应答信号
	Delay5us();
	SCL = 0;   //允许从机释放数据线
}

void SEND_ACK(bit i) //主机发送应答
{
    SCL = 0;
	SDA = i;
	SCL = 1;
	Delay5us();
}

void SEND_DATA(unsigned char Data)  //发送8位数据
{
    unsigned char i;
	for(i=0;i<8;i++)
	{
	  SCL = 0;
		Delay5us();
		SDA = (Data<<i) & 0x80;
		SCL = 1;
		Delay5us();
	}
	SCL = 0;//拉低时钟线，允许从机应答拉低时钟线
	SDA = 1;//拉高数据线，等待从机应答
}

unsigned char READ_DATA()     //接收8位数据
{
    unsigned char i,Data;
	for(i=0;i<8;i++)
	{
	  SCL = 0;
		Delay5us();
		Data = SDA | (Data<<1);
		SCL = 1;
		Delay5us();
	}
	return Data;
}

void AT24C02_WRITE(unsigned char Addr,unsigned char Data)  //写入AT24C02
{
    START();
	SEND_DATA(0xa0);
	READ_ACK();
	SEND_DATA(Addr);
	READ_ACK();
	SEND_DATA(Data);
	READ_ACK();
	STOP();
}

unsigned char AT24C02_READ(unsigned char Addr)          //读出AT24C02
{
	unsigned char Data;
    START();
	SEND_DATA(0xa0);
	READ_ACK();
	SEND_DATA(Addr);
	READ_ACK();
	START();
	SEND_DATA(0xa1);
	READ_ACK();
	Data = READ_DATA();
	SEND_ACK(1);
	STOP();
	return Data;
}

 主函数：

#include "reg52.h"
#include "seg.h"
#include "iic.h"

void Delay100ms()		//@11.0592MHz
{
	unsigned char i, j;

	i = 180;
	j = 73;
	do
	{
		while (--j);
	} while (--i);
}

void main()
{
	unsigned char i;
	AT24C02_WRITE(2,66);
	Delay100ms();
	i = AT24C02_READ(2);
    while(1)
	{
	  SEG_(i);
	}
}

读取到的写入与写出时序如下：

写入时序：

读出时序：

其中发送数据函数中的：SDA = (Data<<i) & 0x80语句执行时间较长，在图中体现在写入数据时SCL为低。