Single chip stopwatch program accurate to one thousandth of a second (with simulation)

This stopwatch program is a program included in the 51hei microcontroller development CD. It can be accurate to one thousandth of a second. The attachment contains simulation files and hex files. Download address: http://www.51hei.com/bbs/dpj-19342-1.html  

#include
#include
#define uint unsigned int
#define uchar unsigned char
sbit duxa=P2^6;
sbit wexa=P2^7;
sbit k1=P1^2;
sbit k2=P1^ 3;
sbit k3=P1^4;
uchar temp,qian,bai,shi,ge;
uint num,a,shu;
uchar code table[]={
0x3f,0x06,0x5b,0x4f,
0x66,0x6d,0x7d,0x07,
0x7f,0x6f,0x77,0x7c,
0x39,0x5e,0x79,0x71};
void init();
void delay(uint z);
void display(uchar num,uchar qian,uchar bai,uchar shi,uchar ge);
void main()
{   
    init();
    while(1)
    {
        display(num,qian,bai,shi,ge);
        if(k1==0)  
        {
            delay(1);
            TR0=0;
            delay(1 );
        }
        if(k2==0)
        {
            delay(1);
            TR0=1;
            delay(1);
        }
        if(k3==0)
        {
          delay(1);
          a=0;
          num=0;
          TR0=1 ;
          delay(1);
        
         }
            
    }
}
void init()
{
    num=0;
    temp=0xf0;
    TMOD=0x01;
    TH0=(65536-1000)/256;
    TL0=(65536-1000)%256;
    EA=1;
    ET0=1;
    TR0=1;
    bai=0;
    shi=0;
    ge=0;
    a=0;
    k1=1;
    k2=1;
    k3=1;
}
void delay(uint z)
{
    uint x,y;
    for(x=z;x>0;x--)
        for(y=110;y>0;y--);
}
void timer0() interrupt 1
{
    TH0=(65536-1000)/256 ;
    TL0=(65536-1000)%256;
    a++;
    
    if(a==9999)
        {
            a=0;
            num++;
            if(num==10)
                num=0;
            
        }  
    shu=a;
    qian=shu/1000;
    bai =shu%1000/100;
    shi=shu%100/10;
    ge=shu%10;
}

void display(uchar num,uchar qian,uchar bai,uchar shi,uchar ge)
{
        wexa=1;
        P0=0xfe;
        wexa=0;
        P0=0;
        duxa=1;
        P0=table[num];
        duxa=0;
        P0=0xff;
        delay(1);

        
        wexa=1;
        P0=0xfd;
        wexa=0;
        P0=0;
        duxa=1;
        P0=table[qian];
        duxa=0;
        P0=0xff;
        delay(1);

        wexa=1;
        P0=0xfb;
        wexa=0;
        P0=0;
        duxa=1;
        P0=table[bai];
        duxa=0;
        P0=0xff;
        delay(1);
       

        wexa=1;
        P0=0xf7;
        wexa=0;
        P0=0;
        duxa=1;
        P0=table[shi];
        duxa=0;
        P0=0xff;
        delay(1);

        wexa=1;
        P0=0xef;
        wexa=0;
        P0=0;
        duxa=1;
        P0=table[ge];
        duxa=0;
        P0=0xff;
        delay(1);
}