A game system is not much fun without a gamepad so I prototyped up a quick one. I am now pretty close to being able to implement a game. Each button has its own little debounce circuit. The output of the buttons are tied high through a resistor, and are shorted when the switch closes. There is also a 0.1uF capacitor across each button. I am hoping the buttons work well enough as is without having to debounce in software.

I did an initial test of modifying my interrupt routine to test if the 'UP' button is depressed and if so to illuminate the LED. It worked!