#include <REGX51.H>
#define uchar unsigned char
sbit P20=P2^1;      
sbit P21=P2^0;
sbit KS=P2^5;      //启动按键
sbit KP=P2^6;      //暂停按键
sbit KC=P2^7;      //复位按键
int ge,shi;
uchar code tab[]={0x3f,0x06,0x5b,0x4f,0x66,
                  0x6d,0x7d,0x07,0x7f,0x6f};   
void delay_ms(unsigned int ms)        //延时
{
 uchar a;
 while(ms--)
 for(a=123;a>0;a--);
}

void display()        //显示
{
  P20=0;
  P0=tab[ge];
  delay_ms(1);
  P20=1;
  P21=0;
  P0=tab[shi];
  delay_ms(1);
  P21=1;
}

void T0_ISR() interrupt 1     //定时器T0中断
{
  uchar time;                 
  TH0=(65536-50000)/256;     //定时初值
  TL0=(65536-50000)%256;
  time++;
  if(time==20)                 //0.05s*20=1s
  {
    time=0;
    ge++;
  }
}

void main()                   //主函数
{  
  TMOD=0x01;               //定时器T0方式1
  TH0=(65536-50000)/256;
  TL0=(65536-50000)%256;
  EA=1;                      //总开关
  ET0=1;                  //允许T0溢出中断
  
  while(1)                  //死循环
  {
     display();
     while(!KS)
     {
       display();
       if(KS)
       TR0=1;
     }
     while(!KP)
     {
       display();
       if(KP)
       TR0=0;
     }
     while(!KC)
     {
       display();
       if(KC)
       TR0=0;
       shi=0;
       ge=0;
     }
     if(ge==10)
     {
       ge=0;
       shi++;
     }
     if(shi==10)
     {
       shi=0;
     }
  }
}