This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
Since the standard Commodore-64 9-pin DIN port is male, it looks like your Koala Pad (with a female plug) is, indeed, intended to work on a C-64, VIC-20, etc. machine. As to whether or not the C-64 Koala Pad can be used on an Apple II, it looks like, probably, it can, if you can find or build an adaptor. This is, really, a guess. It is based upon the capabilities of the C-64 Game port, time constant capacitor values used in the C-64, and the probability that Koala Pad's makers would not wish to make major design changes between Apple and C-64 models. Although C-64 joysticks are of the simple "switcher" type which connect to Game port switch inputs, the C-64 Game port also includes X and Y analog "paddle" inputs. These are at pin 9 (X) and pin 5 (Y). The C-64 manual does not ever seem to specify an optimal max R value for the pots connected to these inputs; but, the capacitor part of the expected R/ C circuit is 1000 pF in each case and the caps go to ground just as they do in the Apple II. In short, the C-64 "paddle" inputs look very much like the Apple II joystick inputs. A try at an adaptor would look something like the following ... To C-64 Koala Pad To Apple II Game Port (9-pin male DIN) (9-pin male DIN) 1 ? 2 ? 2nd Button -> 1 3 ? 4 ? 5 <- PDL1 (Y) -> 8 6 <- main button -> 7 7 <- +5V line -> 2 8 <- GND -> 3 9 <- PDL0 (X) -> 5 The above assumes that the C-64 Koala Pad will use C-64's "Fire Button" input for its main button. The second button would, then, connect to one of the four joystick switch inputs. (Actually, since all of the switch inputs, including the Fire Button, are just inputs to a port IC, any two may be the ones used to handle Koala Pad's buttons.) It should be possible to detect the button lines on the Koala Pad connector using an Ohm meter (on R x 100 range) with one lead connected to the GND pin (pin 8) and using the other lead to check pins 1, 2, 3, 4, and 6. A button lead similar to one on an Apple II should show up as a 500-700 Ohm resistance. Again, we are dealing with guesses. If you decide to try making a converter, be sure to post what you discover. Good luck! By: Mark Wade