Found this page that has a list of some 10 different protocols for sending digital signals from joysticks to a gameport:
https://dosdays.co.uk/topics/joysticks.php
Other than the sidewinder and GriP protocols I have not managed to find any specs for the other protocols. I clearly think I remember from back in the day that using MIDI for extra buttons was a thing so it may be one of those other protocols did, or it could be that I am just wrong.
Found this page that has a list of some 10 different protocols for sending digital signals from joysticks to a gameport: https://dosdays.co.uk/topics/joysticks.php Other than the sidewinder and GriP protocols I have not managed to find any specs for the other protocols. I clearly think I remember from back in the day that using MIDI for extra buttons was a thing so it may be one of those other protocols did, or it could be that I am just wrong.