WA8LMF Home Page | Main Ham Radio Page | Main APRS Page | Updated 02 November 07

Disabling False Identification Of A Serial-Connected GPS Receiver As A Mouse

Many GPS users have experienced the nuisance of having a GPS receiver falsely identified as a mouse on Windows PCs. This occurs if an active GPS device (already outputting data) is already connected to a serial port while Windows is booting. The result is an uncontrollable mouse cursor randomly jumping around the screen. Normally, the only way to stop this is to unplug the GPS serial connection, and then reconnect it.

This problem is caused by Windows "Plug-N-Pray's" imperfect attempts to totally eliminate any need for users to understand the hardware being installed on PCs. Plug-And-Play doesn't just detect the parallel, serial and USB ports on a computer; it goes beyond the port to attempt to identify the printers, modems, mice and other devices plugged into these various ports.

SOMETHING in the NMEA data steam causes Plug-And-Play to falsely conclude that a "Microsoft BallPoint Mouse" (an early clamp-on trackball for laptops) is connected to the serial port.  Windows then proceeds to stupidly forward the entire NMEA GPS data stream into Windows' mouse handling routines, which make the mouse cursor go insane.  When this happens, unplug the offending GPS device and check the Windows Device Manager. You will see an entry under "Mice and other pointing devices" for "Microsoft Ballpoint Mouse on COMn". Just delete this device and then reconnect the GPS.

You can PERMANENTLY stop this behavior with a little-known freeware utility from Microsoft called "ComDisable". This patch program, which you run just once, stops Windows from probing serial ports at boot to identify the attached devices. It DOES NOT prevent the detection of serial ports (either real ones or virtual ones created by USB-to-serial "dongles") themselves.

This utility can be downloaded from the Microsoft webstite at:


A mirrored copy of this utility is also located here on this website at:


Scroll down the page of misc downloadable items and look for  ComDisable.msi ..

This is an installable program in a Windows .MSI installer package that requires that the Microsoft Installer application already be installed on your system. (This will probably already be present on most Windows 2000, XP or Vista systems with recent updates. If it isn't, go to Microsoft's web site and download the freeware "Microsoft Installer".)  

Once, installed, the ComDisable program itself is a single-file command-line utility run from a "Command Prompt" (a.k.a "DOS Box") in Windows.  It only needs to be run once to permanently disable COM port probing.












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