How does the Mac recognize different F-keys on different keyboards?

[JTK Awesome]

Apple's keyboards of course have the special-function "F" keys. As MacOS evolves, so do Apple's keyboards. Especially the F3 and F4 keys (anyone remember Dashboard?!?).

However MacOS will still work with 3rd-party keyboards with older F-key layouts. For example current Keychron keyboards still bring up Launch Pad and Mission Control with F4 and F3.

OTOH sometimes changes to the Mac will break compatibility with the F-keys on 3rd-party Mac keyboards. Under Ventura, my Unicomp Spacesaver M / macOS continued to bring up LP/MC on my Intel Mini (even with the "outdated" F3/F4 keys), but no longer when I upgraded to an M2 Pro Mini.

Do the Macs "read" something off the keyboard? Does MacOS? How do some 3rd-party keyboards retain full F-key functionality, even when it becomes outdated, while others start to lost it?

PS: My keyboard journey has come full circle and I'm back to Apple's own MKB (now with Touch ID). I've been wondering about the above along the way.

 

[kitsunesoba]

My understanding is that for some keys there are multiple keycodes that do the same thing, and different keyboards send different keycodes for the same keys. Apparent changes in behavior result from the OS changing how it interprets one keycode but not the others.

It might also be possible for differences in USB HID implementations and how they interact with the host to cause this kind of behavior, which could explain getting one result with an Intel mac and a different one with an ARM one but I'm less certain of that.

 

[f54da]

USB HID vendor and product id, coupled with a non-standard descriptor. See https://gist.github.com/fauxpark/010dcf5d6377c3a71ac98ce37414c6c4