#include <AT89X51.H>

unsigned char count;

void delay10ms(void)
{
  unsigned char i,j;
  for(i=20;i>0;i--)
  for(j=248;j>0;j--);
}

void main(void)
{
  while(1)
    {
      if(P1_0==0)
        {
          delay10ms();
          if(P1_0==0)
            {
              count++;
              P0=~count;
              while(P1_0==0);
            }
        }
    }
}