void setup() {
  volatile char *dir_f,*dir_b,*dir_a,*dir_d,*in_f,*out_b,*out_a,*out_d;
  volatile long i,j;  
  dir_f=(char*)0x30; dir_b=(char*)0x24;
  dir_a=(char*)0x21; dir_d=(char*)0x2a;
  in_f=(char*)0x2f; out_b=(char*)0x25;
  out_a=(char*)0x22; out_d=(char*)0x2b; 
  while(1){
    for(i=0;i<4;i++){
      *out_b = 1<<i;
      if(*in_f != 0){
        *out_d=*out_b;
        *out_a=*in_f;
        for(j=0;j<200000;j++);
      }
    }
  }
}
void loop() {
}