关于用单片机内部时钟实现时钟计数

用软件实现时钟计数，下载到开发板上，数码管上数字一闪一闪的，刚开始学，不知为什么？求助。程序如下：

 #include<reg52.h>
 #define uchar unsigned char
 #define uint unsigned char
 uchar code led_7seg[]={0x28,0x7e,0xa2,0x62,0x74,0x61,0x21,0x7a,0x20,0x60};
 uchar hour=23,minute=59,second=50,n=0;
 uint count=0;

 void init_timer0(void)    //timer0每2MS中断一次
 {
    TMOD=0x01;
    TH0=(65536-1000)/256;
    TL1=(65536-1000)%256;
    ET0=1;
    TR0=1;
    EA=1;   
 }
 void d1_10ms(void)
 {
    uchar i;
    for(i=200;i>0;i--){}
 }
 uchar kbscan(void)
 {
    uchar sccode,recode;
    P1=0xf0;
    if((P1&0xf0)!=0xf0)
    {
      d1_10ms();
      if((P1&0xf0)!=0xf0)
      {
        sccode=0xfe;
        while((sccode&0x10)!=0)
        {
            P1=sccode;
            if((P1&0xf0)!=0xf0)
            {
                recode=(P1&0xf0)|0xf0;
                return((~sccode)+(~recode));
            }
            else
            sccode=(sccode<<1)|0x01;
        }
      } 
    }
    return(0);
 }
 void timer0_int(void) interrupt 1 using 1
 {
    TH0=(65536-1000)/256;
    TL0=(65536-1000)%256;
    count++;
    switch(n&&0x07)
    {
     case 0:{P0=led_7seg[hour/10];P2=0xfe;}break;
     case 1:{P0=led_7seg[hour%10];P2=0xfd;}break;
     //case 2:{P0=led_7seg[10];P2=0xfb;}break;
     case 3:{P0=led_7seg[minute/10];P2=0xf7;}break;
     case 4:{P0=led_7seg[minute%10];P2=0xef;}break;
     //case 5:{P0=led_7seg[10];P2=0xdf;}break;
     case 6:{P0=led_7seg[second/10];P2=0xbf;}break;
     case 7:{P0=led_7seg[second%10];P2=0x7f;}break; 
     default:break;  
    }
    if(count==500) //1MS时间到调整显示时间
    {
        count=0;
        second++;
            if(second==60)
                {
                second=0;
                minute++;
                }
            if(minute==60)
                {
                 minute=0;
                 hour++;
                 if(hour==24)
                 {
                    hour=0;
                 }  
                }
    }

 }
 void main(void)
 {
    uchar key;
    init_timer0();
    while(1)
    {
     key=kbscan();
     switch(key)
     {
        case 0x11:{if(hour<23)hour++;else hour=0;}break;
        case 0x21:{if(minute<59)minute++;else minute=0;}break;
        default:break;
     }  
    }
 }