Well, the article says

The interface (also used on the Amstrad CPCs) could use any standard Atari (CX-40) joysticks with a second button (on pin 7) which connected to a DE-9 connector. The interface used keyboard scancodes, making joysticks function as if the user was using the numberpad.

So, I guess it should work with any game that uses the standard arrow keys. There are plenty of those.

Jorpho wrote:

Well, the article says

The interface (also used on the Amstrad CPCs) could use any standard Atari (CX-40) joysticks with a second button (on pin 7) which connected to a DE-9 connector. The interface used keyboard scancodes, making joysticks function as if the user was using the numberpad.

So, I guess it should work with any game that uses the standard arrow keys. There are plenty of those.

What about the other buttons aside from the D-Pad? Seems like that would be highly variable. Old (80s) games tended to have their controls spread out all over the keyboard and were... frankly... a mess.

True enough. You could usually count on Ctrl, Alt, and Shift, though, since those tended to be the only keys whose pressing could be reliably detected simultaneously.

I know this is somewhat different, but didn't some of the CHAMP games support using an Atari joystick through a special serial adapter?

That used the parallel port, actually.

If they use scancodes, they should be easier to use with a "Redefine keys" option.

I tried about 20 games an non would accept the Competition Pro joystick. I also tried Champ games - though they only support digital joysticks through Parallel port and an adapter.
In some games you can rdefice keys. I tried this and then move the joystick, but no keys was registered. So i guess its not using scancodes.