Editing Computer mouse (section)

=== Serial interface and protocol ===
[[File:Mouse quadrature encoding Lyon 1980.png|thumb|Signals XA and XB in [[quadrature phase|quadrature]] convey X-direction motion, while YA and YB convey Y-dimension motion; here the pointer (cursor) is shown drawing a small curve.]]

Because the IBM PC did not have a [[quadrature decoder]] built in, early PC mice used the [[RS-232C]] serial port to communicate encoded mouse movements, as well as provide power to the mouse's circuits. The [[Mouse Systems Corporation]] (MSC) version used a five-byte protocol and supported three buttons. The Microsoft version used a three-byte protocol and supported two buttons. Due to the incompatibility between the two protocols, some manufacturers sold serial mice with a mode switch: "PC" for MSC mode, "MS" for Microsoft mode.<ref name="Paul_2002">{{cite web |title=Re: [fd-dev] ANNOUNCE: CuteMouse 2.0 alpha 1 |author-first=Matthias R. |author-last=Paul |work=freedos-dev |date=2002-04-06 |url=https://marc.info/?l=freedos-dev&m=101807226917577 |access-date=2020-02-07 |url-status=live |archive-url=https://web.archive.org/web/20200207130948/https://marc.info/?l=freedos-dev&m=101807226917577&w=2 |archive-date=2020-02-07}}</ref><ref name="Isaja_2003">{{cite web |title=FreeDOS-32&nbsp;– Serial Mouse driver |author-first=Salvatore |author-last=Isaja |date=2003-09-03 |url=http://freedos-32.sourceforge.net/showdoc.php?page=sermouse |url-status=dead |archive-url=https://web.archive.org/web/20090302000300/http://freedos-32.sourceforge.net/showdoc.php?page=sermouse |archive-date=2009-03-02}}</ref>