That pin is an input pin. I understand the signal is active high, so +5vdc is high, so you would put GND or the common for the signal to COM2 and the signal itself to pin 2 port 2. The inputs are very easy to use, these are just bidirectional optos that work from +5vdc to +24vdc. If the signal was active low, or from an open collector output, then you could feed +5vdc into COM2 and the signal itself (GND when active) to pin 2 port 2. If you have any questions, just reply to this message to open a ticket.