I agree with Beminetonight, I have never seen such a RS-485 signal, so it must be wrong.
The examples for RS-485 on the Opta use the normal Arduino RS485 library and normal sketches. Therefor I conclude that after running the initial code, the pins are set properly and nothing special has to be turned on.
Is the Opta open-source ?
Is there a schematic of the Opta ? I could not find it for this topic: Opta analog input accuracy