The most common joystick type in home computers have been Atari-style digital joysticks. Those joysticks are named after Atari, because this joystick type was first introduced in Atari 2600 videogame and then adopted to the home computers introduced on ever since (VIC 20, Commodore 64, Amiga, MSX-computers and even Sinclair Spectrum joystick adapters used this joystick type).
The joystick itself consisted of five switches which are arranged such that four of them correspond to the joystick direction (UP, DOWN, LEFT, RIGHT) and one was for the fire button. The joystick connector was 9 pin D-shell connector. Normally all of those switches are open, but when the joystick is moved from the center position, one or two position switches are closed (according to what direction the stick is turned). The fire button worked so that it closes when the button is pressed. All of the swiches are connected between ground and corresponding signal pin of the joystick connector.
Comment by James : A set of paddles can be connected to the 2600 for games like pong etc
it is a rotary pot like a volume control. 2 paddles are on every connector.
each one has a single button as well, connected to 2 of the joystick direction lines.
Many faqs on the 2600 are incorrect because they dont have the following pins:
5. B Potentiometer Input
9. A Potentiometer Input
The paddles are the Atari CX30 paddle controller
Atari 400, 800, 1200XL, 600XL, 800XL, 65XE, 130XE and 800XE have the same connector and can use both single button joystick and the paddles.
Light pens use pin 6.