Editing Computer mouse (section)

=== PS/2 interface and protocol ===
{{Further|PS/2 port|l1=PS/2 connector}}
[[File:ps-2-ports.jpg|thumb|Color-coded PS/2 connection ports; purple for keyboard and green for mouse]]

With the arrival of the [[IBM Personal System/2|IBM PS/2]] personal-computer series in 1987, IBM introduced the [[eponym]]ous [[PS/2 port]] for mice and keyboards, which other manufacturers rapidly adopted. The most visible change was the use of a round 6-pin [[mini-DIN connector|mini-DIN]], in lieu of the former 5-pin MIDI style full sized [[DIN 41524]] connector. In default mode (called ''stream mode'') a PS/2 mouse communicates motion, and the state of each button, by means of 3-byte packets.<ref>{{cite web |author-first=Adam |author-last=Chapweske |url=http://www.computer-engineering.org/ps2mouse/ |title=Computer Engineering Tips – PS/2 Mouse Interface |publisher=Computer-engineering.org |date=2003-04-01 |access-date=2013-03-10 |url-status=dead |archive-date=2008-09-16  |archive-url=https://web.archive.org/web/20080916065845/http://www.computer-engineering.org/ps2mouse/}}</ref> For any motion, button press or button release event, a PS/2 mouse sends, over a bi-directional serial port, a sequence of three bytes, with the following format:

{|class="wikitable"
|- align=center
!||Bit 7||Bit 6||Bit 5||Bit 4||Bit 3||Bit 2||Bit 1||Bit 0
|- align=center
!Byte 1
|YV||XV||YS||XS||1||MB||RB||LB
|- style="text-align:center;"
!Byte 2
|colspan="8"|X movement
|- style="text-align:center;"
!Byte 3
|colspan="8"|Y movement
|}

Here, XS and YS represent the sign bits of the movement vectors, XV and YV indicate an overflow in the respective vector component, and LB, MB and RB indicate the status of the left, middle and right [[mouse button]]s (1 = pressed). PS/2 mice also understand several commands for reset and self-test, switching between different operating modes, and changing the resolution of the reported motion vectors.<ref name="Paul_2002"/>

A [[IntelliMouse|Microsoft IntelliMouse]] relies on an extension of the PS/2 protocol: the ImPS/2 or IMPS/2 protocol (the abbreviation combines the concepts of "IntelliMouse" and "PS/2"). It initially operates in standard PS/2 format, for [[backward compatibility]]. After the host sends a special command sequence, it switches to an extended format in which a fourth byte carries information about wheel movements. The IntelliMouse Explorer works analogously, with the difference that its 4-byte packets also allow for two additional buttons (for a total of five).<ref>[http://www.microsoft.com/whdc/device/input/mcompat.mspx Retrieved 31 December 2006] {{webarchive|url=https://web.archive.org/web/20080408164755/http://www.microsoft.com/whdc/device/input/mcompat.mspx|date=2008-04-08}}</ref>

Mouse vendors also use other extended formats, often without providing public documentation.<ref name="Paul_2002"/> The Typhoon mouse uses 6-byte packets which can appear as a sequence of two standard 3-byte packets, such that an ordinary PS/2 [[device driver|driver]] can handle them.<ref>{{cite web |title=Keyboard scancodes: The PS/2 Mouse|url=http://www.win.tue.nl/~aeb/linux/kbd/scancodes-13.html |publisher=Win.tue.nl |access-date=2017-12-08}}</ref> For 3D (or 6-degree-of-freedom) input, vendors have made many extensions both to the hardware and to software. In the late 1990s, Logitech created ultrasound based tracking which gave 3D input to a few millimeters accuracy, which worked well as an input device but failed as a profitable product. In 2008, Motion4U introduced its "OptiBurst" system using IR tracking for use as a Maya (graphics software) plugin.

[[File:Usb head Cable.jpg|thumb|right|150px|A USB connector soon superseded the [[PS/2]] keyboard and computer mouse connectors shown above.]]