Microsoft KB Archive/323511

= The Add Hardware Wizard Detects Turned-Off COM Ports in Windows XP =

Article ID: 323511

Article Last Modified on 5/29/2007

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APPLIES TO


 * Microsoft Windows XP Professional
 * Microsoft Windows XP Home Edition

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This article was previously published under Q323511



For a Microsoft Windows 2000 version of this article, see 312291.



SYMPTOMS
If you turn off (disable) a COM port in Device Manager and then run the automatic detection feature for the first time by using the Add Hardware Wizard, the COM port that you turned off is detected as new hardware. This problem occurs if your computer uses Advanced Configuration and Power Interface (ACPI).



CAUSE
Because of the various types of COM port implementations on existing computers, Windows has to enumerate COM ports in various ways for compatibility reasons. Windows must check the COM port devices for duplicates to avoid conflicts with other devices.

If you turn off an ACPI COM port in Device Manager, Windows cannot detect the resource conflict; the COM port is regarded as new hardware when the you run the Add Hardware Wizard.



WORKAROUND
This problem typically does not occur until you restart the computer. To work around this problem, do not click Install Communication Port when the COM port is detected by the Add Hardware Wizard. If you install the port, an additional incorrect COM port is added in Device Manager.

To clear the incorrect COM ports in Device Manager, delete all the inactive COM ports in Device Manager. The next time that you start your computer, the COM ports are detected correctly.

Keywords: kbenv kbprb KB323511

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