Hi Lilow,
Masso input work only with a positive voltage referenced to the Masso -ve of the power supply. It needs to turn on an optocouler LED and any voltage from 4 to 24 volts will do
The input needs to change to High for the Up, Down and ARC to be acknowledged. I imagine if you are looking at the Proma Setup you see the THC switching ground. This is because of the recomendation in the Proma Manual .
COM terminal is a common input terminal connected to the ARC, UP and DOWN relay contacts inside the device, according to the diagram located on the cover (above picture).
Suggested route is to GND at driver/pc end. Do not jumper this connection to the 7-35V negative.
www.masso.com.au
To do this the input is taken high by pull up resistors and as the Proma turns on the Masso inputs change to Low. The 3 THC inputs should be inverted to reverse their state, though now I look at the page I see they are shown as not inverted which is incorrect. Because the inputs are held high normally they should be inverted to change them back to Low in the normal state.
It will depend on your THC how you will connect it.
I hope this helps
Cheers
Peter