void setup() {
  // put your setup code here, to run once:
  volatile char *dirf, *dirk, *out_dataf, *in_datak, x;
  volatile long counter, i;
  
  // directions
  dirf = 0x30; dirk = 0x107;
  out_dataf = 0x31; in_datak = 0x106;
  *dirf = 0x01; *dirk = 0x00;

  counter = 0;

  while (1) {
    x = *in_datak;
    if ((x & 0x01) == 0x01) {
      counter++;
      for (i = 0; i < 100000; i++); // unbounce mechanical button (switch)
    }
    if (counter % 2) {
      *out_dataf = 0x01;
    } else {
      *out_dataf = 0x02;
    }
  }

}

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

}