void setup() {
  // put your setup code here, to run once:
  volatile char *ddrf,*outf;
  volatile long i,j;
  ddrf=0x30;outf=0x31;
  *ddrf=0xff;
  while(1){
    for(j=7;j>3;j--){
      *outf=1<<j;
      for(i=0;i<400000;i++);
      
    }
  }
}