#include <reg51.h>
sbit SW    = P1^7;
sbit IND   = P1^0;
sbit WAVE  = P2^5;
void timer0(void) interrupt 1
  {
    WAVE = ~WAVE;	
  }
void main()
  {
    SW = 1;		
    TMOD = 0x02;
    TH0 = 0xA4;		
    IE = 0x82;		
    while(1)
      {
        IND = SW;	
      }
  }