Spitfire (Fairchild Channel F)
This game has hidden developer credits.
Spitfire is an air combat game just like the plane levels in Atari's Combat, notable as having one of the oldest Easter Eggs in gaming. It doesn't work on a standard cartridge, unfortunately, though it works properly on a multicart.
At the "G?" game selection prompt that appears when the game is booted, normally, one presses 2 on the Channel F's front panel to start a one-player game, and 1 to start a two-player game (yes, it's backwards). 3 and 4 do nothing... or so it seems. In fact, pressing 3 initiates an invisible routine that checks for a passcode. After doing so, the player can then use the Channel F itself to enter the passcode 343242124133231432142314322132342334111223324443. Yes, that's 48 button presses, which must be spaced apart enough for the Channel F's primitive CPU to register them. The screen will flicker for each successful input. If the wrong button is pressed, the game will briefly blank the screen for a second, and then return to the "G?" prompt; the player must press 3 to start the passcode routine and try again.
If the code is successfully input, the following developer credit appears on the screen for a split-second, just long enough to be read:
In total, all of the code related to the routine, including the graphics for the credit and the passcode itself, takes up 226 out of the game's 2,048 bytes, or 11.04% of the ROM, with just 140 bytes of empty space left on the cartridge.