Using gpio.sh invert SDCS option in RUT955 it is possible to invert DCD pin state.
Maybe you have RUT955 to test the feature?
Or can you specify, whether you need same feature in TRB142, which can invert DCD pin once there's traffic to serial interface when Over IP mode is used?
In this mobile application you use, can you see when DCD signal changes? Or you can only see that DCD signal changes when devices wokes up?
How did you trace the signal and drivers? What tools you used?
Best regards, Aliaksandr!