直接贴代码：

iic.h:

#ifndef _IIC_H
#define _IIC_H

//oˉêyéù?÷
void IIC_Start(void); 
void IIC_Stop(void);  
void IIC_Ack(bit ackbit); 
void IIC_SendByte(unsigned char byt); 
bit IIC_WaitAck(void);  
unsigned char IIC_RecByte(void); 
unsigned char ad_read(unsigned char add);
#endif

iic.c:

/*
  程序说明: IIC总线驱动程序
  软件环境: Keil uVision 4.10 
  硬件环境: CT107单片机综合实训平台 8051，12MHz
  日    期: 2011-8-9
*/

#include "stc15f2k60s2.h"
#include "intrins.h"

#define somenop {_nop_();_nop_();_nop_();_nop_();_nop_();}    


#define SlaveAddrW 0xA0
#define SlaveAddrR 0xA1

//总线引脚定义
sbit SDA = P2^1;  /* 数据线 */
sbit SCL = P2^0;  /* 时钟线 */


//总线启动条件
void IIC_Start(void)
{
	SDA = 1;
	SCL = 1;
	somenop;
	SDA = 0;
	somenop;
	SCL = 0;	
}

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

//应答位控制
void IIC_Ack(bit ackbit)
{
	if(ackbit) 
	{	
		SDA = 0;
	}
	else 
	{
		SDA = 1;
	}
	somenop;
	SCL = 1;
	somenop;
	SCL = 0;
	SDA = 1; 
	somenop;
}

//等待应答
bit IIC_WaitAck(void)
{
	SDA = 1;
	somenop;
	SCL = 1;
	somenop;
	if(SDA)    
	{   
		SCL = 0;
		IIC_Stop();
		return 0;
	}
	else  
	{ 
		SCL = 0;
		return 1;
	}
}

//通过I2C总线发送数据
void IIC_SendByte(unsigned char byt)
{
	unsigned char i;
	for(i=0;i<8;i++)
	{   
		if(byt&0x80) 
		{	
			SDA = 1;
		}
		else 
		{
			SDA = 0;
		}
		somenop;
		SCL = 1;
		byt <<= 1;
		somenop;
		SCL = 0;
	}
}

//从I2C总线上接收数据
unsigned char IIC_RecByte(void)
{
	unsigned char da;
	unsigned char i;
	
	for(i=0;i<8;i++)
	{   
		SCL = 1;
		somenop;
		da <<= 1;
		if(SDA) 
		da |= 0x01;
		SCL = 0;
		somenop;
	}
	return da;
}

unsigned char ad_read(unsigned char add)
{
	unsigned char temp;
	IIC_Start();
	IIC_SendByte(0x90);
	IIC_WaitAck();
	IIC_SendByte(add);
	IIC_WaitAck();
	IIC_Stop();
	
	IIC_Start();
	IIC_SendByte(0x91);
	IIC_WaitAck();
	temp=IIC_RecByte();
	IIC_Stop();
	
	return temp;
}

main.c:

#include "stc15f2k60s2.h"
#include "intrins.h"
#include <iic.h>
//----------------------------------------------------
#define uchar unsigned char 
#define uint unsigned int 
//----------------------------------------------------
uchar seg[]={
0xc0,0xf9,0xa4,0xb0,
0x99,0x92,0X82,0XF8,
0X80,0X90,0XFF};//数码管显示值
uchar dianya;
double zhiliang=0;
double jiaqian=0;
uchar flag=0;
uint dis;
uint tim;
uchar er=0,san=5,si=0;wu=0,liu=0,qi=0,ba=0;
//----------------------------------------------------	
void allinit();
void check();
void Timer0Init(void);
void key();
void display(uchar er,san,si,wu,liu,qi,ba);
void Delayms(uint ms);
//----------------------------------------------------	
void main()
{
	allinit();
	Timer0Init();
	while(1)
	{
		key();
		check();
		display(er,san,si,wu,liu,qi,ba);
	}
}	
void allinit()
{
	P2=0xa0;P0=0x00;
	P2=0x80;P0=0xff;
	
	P2=0xe0;P0=0xff;//段选
	P2=0xc0;P0=0xff;//位选
	
}
void check()
{
	dianya=ad_read(0x01);
	if(dianya<(255/2))
	{
		P2=0x80;P0=0xfe;

	}
	else
	{
		P2=0x80;P0=0xff;
	}
	if(flag==1)
	{
		P2=0xa0;P0=0x10;
		dis=(uint)(zhiliang*1000);
		wu=dis/1000;
		liu=dis/100%10;
		qi=dis/10%10;
		ba=dis%10;
	}
	else if(flag==2)
	{
		P2=0xa0;P0=0x00;
		dis=(uint)(jiaqian*100);
		wu=dis/1000;
		liu=dis/100%10;
		qi=dis/10%10;
		ba=dis%10;
	}
}
void key()
{
	if(P30==0)
	{
		Delayms(5);
		if(P30==0)
		{
			EA=1;
			ET0=1;
			flag=1;
		}
		while(!P30)
		{
			display(er,san,si,wu,liu,qi,ba);
		};
	}
	
	if(P31==0)
	{
		Delayms(5);
		if(P31==0)
		{	
			EA=0;
			ET0=0;
			flag=2;
		}
		while(!P31)
		{
			display(er,san,si,wu,liu,qi,ba);
		};
	}
}
void display(uchar er,san,si,wu,liu,qi,ba)
{	
	P2=0xe0;P0=0xff;
	P2=0xe0;P0=seg[er]-0x80;//段选
	P2=0xc0;P0=0x02;//位选
	Delayms(1);
		
	P2=0xe0;P0=0xff;
	P2=0xe0;P0=seg[san];//段选
	P2=0xc0;P0=0x04;//位选
	Delayms(1);
	
	P2=0xe0;P0=0xff;
	P2=0xe0;P0=seg[si];//段选
	P2=0xc0;P0=0x08;//位选
	Delayms(1);
	
	P2=0xe0;P0=seg[wu];//段选
	P2=0xc0;P0=0x10;//位选
	Delayms(1);
	
	P2=0xe0;P0=seg[liu]-0x80;//段选
	P2=0xc0;P0=0x20;//位选
	Delayms(1);
	
	P2=0xe0;P0=seg[qi];//段选
	P2=0xc0;P0=0x40;//位选
	Delayms(1);
	
	P2=0xe0;P0=seg[ba];//段选
	P2=0xc0;P0=0x80;//位选
	Delayms(1);

}
void Delayms(uint ms)		//@11.0592MHz
{
	unsigned char i, j,k;
	for(k=ms;k>0;k--)
	{
		_nop_();
		_nop_();
		_nop_();
		i = 11;
		j = 190;
		do
		{
			while (--j);
		} while (--i);
	}
}
void Timer0Init(void)		//1毫秒@11.0592MHz
{
	AUXR |= 0x80;		//定时器时钟1T模式
	TMOD &= 0xF0;		//设置定时器模式
	TL0 = 0xCD;		//设置定时初值
	TH0 = 0xD4;		//设置定时初值
	TF0 = 0;		//清除TF0标志
	TR0 = 1;		//定时器0开始计时
}
void timer0() interrupt 1
{
	tim++;
	if(tim%100==0)
	{
		zhiliang=zhiliang+0.001;
		jiaqian=jiaqian+0.005;
		if(tim==1000)
		{
			tim=0;
			if(zhiliang==99.99)
			{
				flag=2;
			}
		}
	}
}