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