Technically this is a keyboard.Since MAME does use keys for many of the game controls and many of the classic arcade games had only buttons or digital sticks the easiest way to make it work was to drop in a keyboard controller. The stick and buttons generate the proper keys that are set as default in MAME, i.e. the stick produces the arrow keys and the first button is Ctrl for fire.
Internally the switches are wired to the keyboard matrix in the proper positions.
This unit was done with our (now discontinued) KeyWarrior24-8-MOD, which has a fixed key layout, so the switches had to go where the key codes are. I plan to redo it with our brand new KeyWarrior28-MOD which is fully programmable. This will allow me to arrange the keys so there is no way for phantom keys, even without the use of diodes.