Upgrading from Garmin SL-40 to SL-30 question

I am considering changing out my Garmin SL-40 to a Garmin SL-30 for the benefit of an extra VOR/ILS in my RV-7. I know that with the SL-30 I will also have the ability of an extra bearing pointer on my 4500 screen. What wiring does it entail to make this happen?

Thanks in ADVANCE for your reply

Terry

Wire it to a serial port, two wires TXD and RXD