Oooh, I just figured out how any arbitrary button on the display can execute any arbitrary button or m-code function in mach3, through 1 simple brain, 1 simple script, 1 Modbus register, and 1 invisible dro and 1 invisible led. It looks feasible to handle LEDs and DROs on the display in a similar fashion.
That means you could just put a button, dro, or led on the display, and it will work without having to do anything in mach, except add your own m-code script files for custom functions.
If I can just make the display customizable, that will be something...
As it is, each function has a separate screen control hard-wired to a brain and Modbus address in mach3, which is very cumbersome to configure all those functions individually on the display and in mach3, and each one adds to the Modbus payload.
One thing I haven't figured out yet is how to execute g-code or view g-code on the display, that's something I'd like to have.