#include <reg51.h>
void T0Delay(void);
void main(void)
  {
   while(1)		
    {
      P1=0x55;		
      T0Delay();	
      P1=0xAA;		
      T0Delay();
    }
  }
void T0Delay()
  {	
    TMOD=0x01;		
    TL0=0x00;		
    TH0=0x35;		
    TR0=1;			
    while(TF0==0);	
    TR0=0;			
    TF0=0;			
  }