#include <reg51.h>
void MSDelay(unsigned int);
void main(void)
  {
    while(1)      		
      {
        P0=0x55;  		
        P1=0x55;
        P2=0x55;
        MSDelay(250); 	
        P0 = 0xAA;   	
        P1 = 0xAA;
        P2 = 0xAA;
        MSDelay(250);  	
      }
  }
void MSDelay(unsigned int itime)
  {
  unsigned int i, j;
  for(i=0;i<itime;i++)
    for(j=0;j<1275;j++);
 }