code: private void open() throws ModbusIOException {
          if (commPort != null && !commPort.isOpen()) {
              setTimeout(timeout);
              try {
                  commPort.open();
              }
              catch (IOException e) {
                  throw new ModbusIOException(String.format("Cannot open port %s - %s", commPort.getDescriptivePortName(), e.getMessage()));
              }
          }
      }
docs: Opens the port if it isn't already open
  
  @throws ModbusIOException If a problem with the port