Retrocomputing Asked by colmde on August 25, 2021
The game Creatures 2 on the Commodore 64 had an unusual cheat to get infinite lives which unlike most things on the Internet that are said to “really work” really worked!
What you had to do was lick your finger and then rub it on the joystick port. IIRC A picture of a mouse (I believe he was a character from another game) would appear which would flap his arms as you rubbed the port, and eventually he’d turn grey to indicate the cheat was active.
I know it sounds weirdly perverted, but it actually did the trick!
My question is, how?
Originally intended for use with paddle input devices (and, like everything else on the C64, since exploited to the limit), the C64 has A/D converters readable from code exposed on the joystick ports. It also has power rails exposed. Combine that with the lowered resistance of a moist finger and it is absolutely possible to read changing resistance values off the A/D converter when touching the port; I remember doing this gimmick for a demo back in the day.
Correct answer by Retrograde on August 25, 2021
IIRC the official way to enable this cheat was to wiggle the joystick left and right, which moved the creatures arms. You had to do this at an extremely rapid rate and at such time the cheat would activate.
We had a disassembled joystick and discovered that if you just held down the left and right microswitches at the same time the cheat would activate instantly. I suspect the wiggle detection code was written in such a way that this was interpreted as the required fast wiggle.
Coming back to the original question and as alluded to in one of the other answers, it's possible that the wet finger shorted pins on the port in a similar way to having both left and right directions activated, and thus enabled the cheat.
Answered by wlf on August 25, 2021
Assuming it really does work and we are not hunting an urban legend:
Every game needs some sort of cheat mode during development and testing in order to be able to test and verify later levels of the game that would otherwise take considerable time to reach.
It could very well be that the cheat mode is activated by detections from the joystick ports of conditions not achievable with a normal joystick (like, for example, opposite directions triggered). This would, in game development, normally have been triggered by specific port adapters (a "dongle") that connect those "impossible" joystick lines by wires or switches, or even active components.
Depending on the impedance of the C64 joystick inputs, a wet finger directly on the port pins might be able to close the very same connections and activate the cheat mode.
Answered by tofro on August 25, 2021
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