You have to do this with an Event.
https://v-control.com/wiki/doku.php/device_editor#events
The Ack string of the Event should be
</System>
(in Hex, maybe followed by a 0D0A), because the message is only complete if it is terminated by that.
Then you can Parse the ioResult (which contains the received message), fetch your data and fill device variables with that.
