public function deviceClose()
    {
        if ($this->_dState !== SERIAL_DEVICE_OPENED) {
            return true;
        }

        if (fclose($this->_dHandle)) {
            $this->_dHandle = null;
            $this->_dState = SERIAL_DEVICE_SET;

            return true;
        }

        trigger_error("Unable to close the device", E_USER_ERROR);

        return false;
    }