代码中有详细的注释：

#include<reg52.h> 


sbit WEI=P2^7;
sbit DUAN=P2^6;
sbit L1=P3^4;

unsigned char code dofly_DuanMa[11]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x40};// 显示段码值0~9
unsigned char code dofly_WeiMa[]={0xfe,0xfd,0xfb,0xf7,0xef,0xdf,0xbf,0x7f};//分别对应相应的数码管点亮,即位码

void delay(int t)
{
   while(t--);
}
  
//第一个参数i代表控制第几个数码管，n代表要显示的数字
void Screen(int i,int n)
{

     P0=0;
     DUAN=1;
	 DUAN=0;
     
     P0=dofly_WeiMa[i];
     WEI=1;
	 WEI=0;
    
     P0=dofly_DuanMa[n]; 
     DUAN=1;  
     DUAN=0;

}



int sec;
int num;
int i;
int flag;



int main()
{
    flag=1;
    i=0;
    num=0;
	sec=0;
  	WEI=0;
  	DUAN=0;

   //开中断	 
 	EX0=1;         
 	IT0=1;         
  	EX1=1;         
 	IT1=1;         
  
    //定时器初始化
    TMOD |= 0x01;	  		     
    EA=1;           
    ET0=1;          
    TR0=1;
   

   L1=0;


 
   while(1)
   {
         
     
     if(num>=10)
	 Screen(3,num/10);

	 Screen(4,num%10);
     delay(10);
     Screen(5,10);

	 Screen(6,sec/10);
     Screen(7,sec%10);
		
	}
   
      return 0;
}

void Timer_0() interrupt 1 using 1
{
   
   
   TH0=(65536-10000)/256;
   TL0=(65535-10000)%256;
   if(flag==1)
   {
     i++;

	    sec++;
		if(sec==100) //0.1ms
		sec=0;

     if(i==101)//1s
     {
        i=0;
	    num++;
	    if(num==15)
	    num=0;
     }
   }
}

void ACTION1() interrupt 0 
{
    flag=!flag;

}


void ACTION2() interrupt 2 
{
   
	  if(flag==0)
	  {
	    Screen(7,0);
	    num=0;
		sec=0;
	  }
}

</reg52.h>