Computer mouse: Difference between revisions

Revision as of 18:26, 17 September 2024

Revision as of 09:58, 12 October 2024

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In the 1970s, the [[Xerox Alto]] mouse, and in the 1980s the Xerox [[optical mouse]], used a [[rotary encoder#Incremental rotary encoder|quadrature-encoded]] X and Y interface. This two-bit encoding per dimension had the property that only one bit of the two would change at a time, like a [[Gray code]] or [[Johnson counter]], so that the transitions would not be misinterpreted when asynchronously sampled.<ref name="Lyon_1981" />

The earliest mass-market mice, such as on the [[Apple mouse#Models|original Macintosh]], [[Amiga]], and [[Atari ST]] mice used a [[D-subminiature]] 9-pin connector to send the quadrature-encoded X and Y axis signals directly, plus one pin per mouse button. The mouse was a simple optomechanical device, and the decoding circuitry was all in the main computer.

The [[DE-9 connector]]s were designed to be electrically compatible with the [[joystick#Electronic games|joysticks]] popular on numerous 8-bit systems, such as the [[Commodore 64]] and the [[Atari 2600]]. Although the ports could be used for both purposes, the signals must be interpreted differently. As a result, plugging a mouse into a joystick port causes the "joystick" to continuously move in some direction, even if the mouse stays still, whereas plugging a joystick into a mouse port causes the "mouse" to only be able to move a single pixel in each direction.