I use a Vogatek supergun for my JAMMA test rig which accepts Megadrive joypads as the inputs and is controller via the PICs onboard. The problem with this is that if there is no controller inserted into one or both of these ports then it activates random button presses causing all sorts of unwanted actions to happen. After a bit of research and searching the net I found a link from a guy who has made an update for these PICs.
I have not been able to get in touch with the guy that made this but it is excellent and I am putting it up on here for anyone that may find it useful. If the original author wants me to remove this then please let me know, or just let me know who you are anyway as a big thanks is in order to you.
Just erase the currently installed PICs and replace program the attached .HEX file to it.
With this mod the A button is required to be pressed before any other button will register, this stops the random button presses from happening.
Also, with a tiny 2 wire mod to the board you can coin up from the controller by pressing START and C. All information is included within the ZIP file.
All credit goes to Matt-MCJDesign for these files, I am merely hosting them.
Supergun Controller Mod