FR22 assignment of buttons to mission editor entries
A to D is local air coordination channels (ie tower, approach, area etc) selected by the right rotary. The number is the same as the airfield reference number, so if the airfield has reference number 9013 then set 13 with the rotary to be able to contact the ATC. Since DCS only has one person to talk to (“ATC”) all these channels gets you to the same entity. Selecting ALLM on the rotary (”allmän” = general) switches the layer so E, F and G is selectable. IRL they where some type of ground control IIRC (I guess national?).
H is the emergency channel, similar to NATO GUARD I believe.
Special 1-3 is some type of extra channels, don’t know what they where used for IRL but it might have been communicating with ground forces or something.
Minus is the manual selector on the front panel.
The left rotary and buttons below are for contacting different flights, you can look up the number in the kneeboard.