Doom II

Codes are entered via the game\'s internal keyboard, which is accessible during gameplay while in first-person view, or while viewing one of the game\'s menus; It is not accessible while in Automap mode.
To access the keyboard, simultaneously depress, then release, all 4 Action buttons (the 4-button cluster on the right side of the face of the Zodiac), then depress the analog controller/joystick once.