public void unknownInstruction(int pc, int op) {
    switch (op) {
    case SLEEP:
      cycles += 100;
      break;
    case LOAD_FILE:
      if (acc == 0)
        monitor.info("**** LOAD FILE! ***** PC = " +
            Integer.toString(pc, 16) + " => " +
            Integer.toString(rindex, 16));
      else
        monitor.info("**** VERIFY!    ***** PC = " + pc + " => " + rindex);
      int len;
      int mptr = memory[0xbb] + (memory[0xbc] << 8);
      monitor.info("Filename len:" + (len = memory[0xb7]));
      String name = "";
      for (int i = 0; i < len; i++)
        name += (char) memory[mptr++];
      name += '\n';
      int sec = memory[0xb9];
      monitor.info("name = " + name);
      monitor.info("Sec Address: " +  sec);
      int loadAdr = -1;
      if (sec == 0)
        loadAdr = memory[0x2b] + (memory[0x2c] << 8);
      if (list != null) {
        if (list.readFile(name, loadAdr)) {
          acc = 0;
        }
      }
      pc--;
      break;
    }
  }