I’m using a RealSimGear GTN 650 with Reality XP GTN 650 in Prepar3D v4.

The RealSimGear Device Interface detects the hardware and shows button activity and commands such as:

GPS DIRECTTO BUTTON
GPS CURSOR BUTTON

So the hardware is being seen.

In Reality XP, Use Simulator GPS Commands is enabled.

If I assign the Direct-To function to a keyboard key in P3D, the Reality XP GTN responds correctly.

But when I press the Direct-To button on the RealSimGear hardware, Reality XP does not respond, even though the Device Interface shows the button press and command.

I also tested the RealSimGear hardware against a default P3D GPS, and the hardware button works there.

So the problem appears to be that the RealSimGear hardware commands are not controlling the Reality XP GTN, even though:

the hardware is detected
the Device Interface is seeing the button presses
and the same function works from a P3D keyboard assignment

Has anyone run into this with RealSimGear + Reality XP in P3D v4?

In case anyone else has this issue it was as simple as selecting the Com1 icon in the device interface rather than the Com2. I had configured the GPS to use Com1 and the interface needed to know that bit of information I guess.