void setup() {
  // put your setup code here, to run once:
  volatile long i,j;
  
  volatile char *dirf,*dirk,*dira,x;
  volatile char *outf,*ink,*outa;

  dirf = 0x30;  dirk = 0x107;  dira = 0x21;
  outf = 0x31;  ink = 0x106;   outa = 0x22;
  *dirf = 0x0F; *dirk = 0x00;  *dira = 0x0F;
  *outa = 0x05; 

  while(1)
  {
    for(i=0;i<4;i++){
      *outf = 1 << i;
      *outa = *ink; //read
      if(*ink != 0)
      for(j=0;j<500000;j++);
    }
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}