void setup() {
  volatile char *dirf, *dirk, *outf, *ink, x, i;
  volatile long j;
  char previous_state = 0;
  char current_state;

  outf = (char*)0x31; 
  ink = (char*)0x106;
  *dirf = 0xff; 
  *dirk = 0x00;
  i = 0x00;

  while (1) {
    x = *ink;
    current_state = x & 0x01; 
    if (current_state == 1 && previous_state == 0) {
      i++;
      if (i > 9) i = 0;
      for (j = 0; j < 100000; j++);
    }

    previous_state = current_state;

    if ((x & 0x02) == 0x02) {
      i--;
      if (i < 0) i = 9;
      for (j = 0; j < 100000; j++);
    }
    switch (i) {
      case 0: *outf = 0x3f; break;
      case 1: *outf = 0x06; break;
      case 2: *outf = 0x5b; break;
      case 3: *outf = 0x4f; break;
      case 4: *outf = 0x66; break;
      case 5: *outf = 0x6d; break;
      case 6: *outf = 0x7d; break;
      case 7: *outf = 0x07; break;
      case 8: *outf = 0x7f; break;
      case 9: *outf = 0x6f; break;
    }
  }
}

void loop() {

}