Difference between telemetry ports

I just got a new Iris + along with a fpv camera, MinimOSD, and transmitter/receiver. If I plug the OSD into the Telem 1 port, it works fine. If I plug it into the Telem 2 port, i get "waiting for Mavlink heartbeat"
What is the difference between the two ports and can i change them to both out put the same stuff, since need Telem 1 plugged in to my 3DR radio.

port 1 is for on screen display and port 2 til telemetery.
according to this page.