Currently, I am programming a SimConnect based software to control my DIY A320 FCU. I built this peace of hardware some years ago for the FSX based AEROSOFT Airbus A320/A321. The software was designed as an in-process gauge (DLL).
Targeting MSFS 2020 now, I decided to re-design my software and set it up as an out-of-process EXE. The software works, I am able to control most of the FCU (did not implement AP1, AP2 and VS yet).
But there is one thing which I cannot figure out: the interaction of AUTOPILOT ALTITUDE LOCK VAR and AUTOPILOT ALTITUDE SLOT INDEX in SimConnect on the one hand and the behaviour of the A320FCU in MSFS on the other hand.
As far as I figured out, AUTOPILOT ALTITUDE LOCK VAR seems to represent what is used by the FMS, not what is shown in the display, i.e. when the altitude knob of the FCU is tuned in MSFS, the display value changes immediately but AUTOPILOT ALTITUDE LOCK VAR does NOT change until the altitude knob is pushed or pulled.
So far I have not been able to find a variable which represents the displayed value. In the case mentioned above, such a variable should represent the displayed value and NOT the value the FMS is using for flight.
Without such a variable, I can only set AUTOPILOT ALTITUDE LOCK VAR from my FCU hardware which means that the plane will use that value immediately. Therefore, I cannot tune e.g. the go around altitude into the ALT window of the FCU without pressing/pulling the ALT knob, therefore still folowing the current altitude until the moment I will press/pull the knob.
I know that there are many things in MSFS which are not available via SimConnect variables (and events). But I did not know about the “… SLOT INDEX” variables, too, until some knowing member of this community gave me a hint. Sadly, SimConnect documentation is still uncomplete.
Greetings from Germany,
PS: Are there any variables which reflect the status of LOC and APPR buttons?