#define TIMER0_COUNT 0xEE11 /* 10000h-((12,000,000/(12*200))*/
code seven_seg[16]={0XC0,0XF9,0XA4,0XB0,0X99,0X92,0X82,0XF8,0X80,
                   0X90,0X88,0X83,0XC6,0XA1,0X86,0X8E};
code scan[4]={0X0E,0X0D,0X0B,0X07};
unsigned char counter[4]={0,0,0,0};
unsigned char timer0_tick,k=0;
static void timer0_isr(void) interrupt TF0_VECTOR using 1
{
  TR0=0;
  TL0=(TIMER0_COUNT & 0x00FF);
  TH0=(TIMER0_COUNT >> 8);
  TR0=1;
  P1=seven_seg[counter[k]];
  P0=scan[k];
  k++;
  if(k==4) k=0;
  timer0_tick++;
  if (timer0_tick==200) timer0_tick=0;
}
static void timer0_initialize(void)
{
  EA=0;
  timer0_tick=0;
  TR0=0;
  TMOD &= 0XF0;
  TMOD |=0x01;
  TL0=(TIMER0_COUNT & 0x00FF);
  TH0=(TIMER0_COUNT >> 8);
  PT0=0;
  ET0=1;
  TR0=1;
  EA=1;
}
void main (void)  
{
  unsigned char c=0;
  char ch;
  timer0_initialize();
  do {
    ch=gotkey();
    for(c=3;c>0;c--)
        counter[c]=counter[c-1];
        counter[0]=ch;
    } while(1);
}