//主函数
#include <reg52.h> //用52头文件编程
#include <iic.h> //iic头文件

sfr P4=0xc0;                           //定义P4管脚

sbit C1=P3^0;                          //矩阵按键相关
sbit C2=P3^1;
sbit C3=P3^2;
sbit C4=P3^3;
sbit R1=P3^4;
sbit R2=P3^5;
sbit R3=P4^2;
sbit R4=P4^4;

unsigned char s16=0;                    //按键s16输入按键
unsigned char s12=0;                    //按键s12密码修改按键
unsigned char s8=0;                     //按键s8清除按键
unsigned char a1;                       //修改密码时的参数
unsigned char a2;
unsigned char a3;
unsigned char a4;
unsigned char a5;
unsigned char a6;
unsigned char b1=0;                      //
unsigned char b2=0;                      //输入完成的标志
unsigned char b3=0;                      //密码输入正确的标志
unsigned char b4=0;                      //密码输入错误的标志
unsigned char b5=0;                      //输入密码达到6位时的标志
unsigned char b6=0;                      //密码输入正确时，修改密码的标志
unsigned char c1=8;                      //读取上次存储密码第一位
unsigned char c2=8;                      //读取上次存储密码第二位
unsigned char c3=8;                      //读取上次存储密码第三位
unsigned char c4=8;                      //读取上次存储密码第四位
unsigned char c5=8;                      //读取上次存储密码第五位
unsigned char c6=8;                      //读取上次存储密码第六位
unsigned char c7;                        //首次上电的密码存储相关
unsigned char moshi=0;                   //显示的模式
unsigned char count_1;                   //中断计数
unsigned long mima=888888;
unsigned long mima_1=21;                 //密码第一位
unsigned long mima_2=21;                 //密码第二位
unsigned long mima_3=21;                 //密码第三位
unsigned long mima_4=21;                 //密码第四位
unsigned long mima_5=21;                 //密码第五位
unsigned long mima_6=21;                 //密码第六位
unsigned long mima_7=0;                  //密码错误时显示 原数
unsigned char num;                       //按键代表的数
unsigned char i;                         //选择第几位密码输入
unsigned char dat;                       //AT24C02写入的数据
unsigned char smg_buff[8];               //数码管缓存
unsigned char code SMG_Duan[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,
                               0x88,0x80,0xc6,0xc0,0x86,0x8e,0xbf,0x7f,0x8c,0x86,0xc8,0xff};
//数码管段选0 1 2 3 4 5 6 7 8 9 a b c d e f - . P E N 关闭

void Read_mima();
															 
void Delay(unsigned int t)               //延时函数
{
	while(t--);
}
void Init_system()                       //系统初始化函数
{
  P2=(P2 & 0x1f)|0x80;                   //关闭LED灯
	P0=0xff;
	
	P2=(P2 & 0x1f)|0xa0;                   //关闭继电器和蜂鸣器
	P0=0x00;
	P2=0x00;
}
/

#include "reg52.h"
#include "intrins.h"

#define DELAY_TIME 5

#define SlaveAddrW 0xA0
#define SlaveAddrR 0xA1


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

void IIC_Delay(unsigned char i)
{
    do{_nop_();}
    while(i--);        
}
//总线启动条件
void IIC_Start(void)
{
    SDA = 1;
    SCL = 1;
    IIC_Delay(DELAY_TIME);
    SDA = 0;
    IIC_Delay(DELAY_TIME);
    SCL = 0;	
}

//总线停止条件
void IIC_Stop(void)
{
    SDA = 0;
    SCL = 1;
    IIC_Delay(DELAY_TIME);
    SDA = 1;
    IIC_Delay(DELAY_TIME);
}

//发送应答
void IIC_SendAck(bit ackbit)
{
    SCL = 0;
    SDA = ackbit;  					// 0应答 1非应答
    IIC_Delay(DELAY_TIME);
    SCL = 1;
    IIC_Delay(DELAY_TIME);
    SCL = 0; 
    SDA = 1;
    IIC_Delay(DELAY_TIME);
}

//等待应答
bit IIC_WaitAck(void)
{
    bit ackbit;
	
    SCL  = 1;
    IIC_Delay(DELAY_TIME);
    ackbit = SDA;
    SCL = 0;
    IIC_Delay(DELAY_TIME);
    return ackbit;
}

//通过iic发送数据
void IIC_SendByte(unsigned char byt)
{
    unsigned char i;

    for(i=0; i<8; i++)
    {
        SCL  = 0;
        IIC_Delay(DELAY_TIME);
        if(byt & 0x80) SDA  = 1;
        else SDA  = 0;
        IIC_Delay(DELAY_TIME);
        SCL = 1;
        byt <<= 1;
        IIC_Delay(DELAY_TIME);
    }
    SCL  = 0;  
}

//从iic上接收数据
unsigned char IIC_RecByte(void)
{
    unsigned char i, da;
    for(i=0; i<8; i++)
    {   
    	SCL = 1;
	IIC_Delay(DELAY_TIME);
	da <<= 1;
	if(SDA) da |= 1;
	SCL = 0;
	IIC_Delay(DELAY_TIME);
    }
    return da;    
}

#ifndef _IIC_H
#define _IIC_H


void IIC_Start(void); 
void IIC_Stop(void);  
bit IIC_WaitAck(void);  
void IIC_SendAck(bit ackbit); 
void IIC_SendByte(unsigned char byt); 
unsigned char IIC_RecByte(void); 

#endif

总结一下：我认为关键是首次写入的时候密码为888888，再次断电的时候仍让能用上次保存的密码而不是原始密码。因为AT24C02拥有掉电不丢失的特性，所以我认为不能每次从新上电都是原始密码888888。我的解决方法是在主函数里判断了AT24C02的第8个地址是否大于0，如果大于0那么就写入初始密码888888，新的开发版的第八个地址的数据基本上都是大于0的，如果没有初始化成功，需要修改两个地方。又不懂的地方欢迎留言。