Garmin GTR 200 questions

Good day RV friends
I have two questions regarding the Garmin GTR200 radio:
1 : Can someone please explain to me in layman's terms what is the purpose of the Discrete function is. I am takiling about DISC 1 (pin 2) and DISC 2 ( pin 22)
And
2 : What is the difference in the AUX AUDIO IN HI ( pin 32) and AUX AUDIO IN LO ( pin 31) Heck, what is HI and LO?
Regards
Arie

Discrete 1 and 2 provide you the option of making those buttons do what ever you want ( within reason). The hi / lo that garmin uses is their version with hi being the signal wire and lo being the negative or ground side on the signal. The GTR 200 is a stereo radio so you have also left and right in addition to a " ground "or lo wire connection. Great radio

Arie,

The GTR discrete inputs are active low inputs. This means that the logic for the input is true when the pin is connected to ground (or less than 375 Ohms to be precise). You can trigger a function by tying that pin to ground through a momentary switch. The functions of the discrete inputs are given in Table 3-7 of the GTR 200 installation manual. In summary, you can perform COM flip-flop, COM Monitor, Intercom PTT or cycle through user frequencies.

Thanks,
Levi

I used the discrete inputs on both the GTR-200 and the GMA-240/5, as shown below on my Tosten CS-8 stick legend image, when I wired my control column harness.

I left tails for the unused, second, discrete inputs in case I later decide I wanted to use them for something.