1188 - RESETTING YOUR COMPUTER'S COM PORT ASSIGNMENT

Matthew L. Bisque — Tue, 23 Aug 2005 20:00:41 GMT

Software Bisque Knowledge Base Article - 1188

RESETTING COM PORT NUMBER ASSIGNMENTS UNDER WINDOWS

ISSUE

How can I reset the COM port assignments on my Windows computer?

RESOLUTION

Each time a USB device is plugged into a USB port, Windows "rediscovers" the device. This can lead to having many different COM port assignments, and cause hardware compatibility issues. Resetting the COM database may resolve these issues. Below is a procedure that I and others have used successfully in the past.

After repeated installations of various USB-serial converters, the assigned com ports continue to increase with the operating system reserving a COM number for every USB device that was ever installed. Even though it is possible to reassign a com number in the Device Manager, some vestige of the old assignments remain and may be polled as part of COM interaction with the application and the operating system.

CAUTION: This procedure requires editing the registry. See:

http://www.bisque.com/support/sbkb2/1059.asp

before proceeding.

Uninstall any USB-serial converter drivers or other com port add-in PC cards or PCI cards in the Device Manager. Do this by right clicking on the device in the Ports branch of Device Manager. If you have any kind of multiport serial adapters, uninstall those as well. After they are uninstalled, unplug the USB-serial converter(s)
Click Start | Run, type RegEdit and then click OK.
Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter key.
Highlight COM Name Arbiter.
Select File | Export.
Pick a suitable name and location to save this file. Note where you put it. In case of problems, you can restore exactly where you were with this branch by running RegEdit and clicking File | Import to import this file.
Right-click on the ComDB entry on the right side of the window, and then click Modify.
On the Edit Binary Data window, highlight all the values and delete them (set them to 0) by hitting the delete key on the keyboard. Do not delete the ComDB key, just clear the value data (set it to zero) and then click OK.

Click File | Exit to exit the Registry Editor and restart the computer.
All of your native COM ports will be discovered automatically.
Any serial-USB converters will need to be reinstalled but they should start with the first COM number after your native COM ports.

APPLIES TO

Windows XP and Windows 2000 operating systems.

KEYWORDS

SBKB, Paramount, ME, connect, failure, erratic, slew, delay, timeout, serial port

Last Reviewed: 03/30/2005