Change Comm Port Number

How do you remove the "in use" status in a comm port number when the device that uses the comm port number is not connected?

I have used several products (from different manufacturers) of USB to Serial converters. I will call the different brands of converters device A, device B, etc.. and USB A, USB B, etc.. to identify the different USB ports for simplicity.

Here are the steps and results to better illustrate:

           DEVICE       USB Port        Assigned Comm Port Number
1.            A                  A                                  1
2.            A                  B                                  2
3.            A                  C                                  3
4.            B                  A                                  4
5.            B                  B                                  5

As we can see, each device occupies a comm port number for each USB port it is connected to (even when it is the same device connected to a different USB port).

Now, the problem is, I have an application which only accepts ports 1-16. I have already used several brands of USB-Serial converters that the ports 1-20 are already occupied. Now, when I connect a new USB-Serial converter, the comm port number assigned is already 20+. I tried to manually change the comm port number through the device manager, but all the lower numbers are already in use. The devices that occupies the lower numbers are not in the device manager since they are not connected (they are already not working).

Is there a way to "release" the comm port numbers from the converts which are not connected?

Let me know if anything isn't clear.

P.S. Same problem on both WinXP and Win7.

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See if this will work for you.
USBDeview   (free)

List, edit, delete the USB list in Windows.
ThomasianAuthor Commented:
It got worse!

The application uninstalls the driver but doesn't free the comm port number. Now, when I plugged in the device, it reinstalls the driver and assigns a new comm port number. Previously, I still have 1 device at Comm2, but now I can't even access that anymore.
wow. That's a new one.   : (

Last post here:

"XP has a bug associated with assigning com port addresses to USB
devices. Every time the device is connected, it is assigned a
higher com port number. In the advanced section of the com port
setup in device manager when the device is connected, you can
just reassign the port number for the device to a lower port
number that you know is not in use, and ignore the windows
warning. I've done this with my USB/serial port adapter and XP
seems to remember the assigned com port after that. Check the
link below for some info.  "

Here's a .PDF with another method:

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ThomasianAuthor Commented:
I tried the suggestion of ignoring the warning when setting the comm port number to "in use" numbers, and it works! Will I experience problems when doing this without first uninstalling the driver of the previous device? Or if I mistakenly assigned it to a comm port which will still be used in the future?

I also tried the other suggestion of adding the system variable and using the command prompt to show hidden devices. There is a show hidden devices option in the device manager. When checked, some additional devices are shown in the device manager (e.g. Non-Plug and Play Drivers), but no unplugged comm port was shown. Any idea why it doesn't work on my computers? I tried it on both Win7 and WinXP.
>> Any idea why it doesn't work on my computers?

Not really. I don't run XP and don't use that many USB devices, to have "in depth" experience with this issue.
You shouldn't have a problem about drivers not uninstalled, but you might get a "conflict error" if the port is already being used. Depends on what the devices think about sharing.
ThomasianAuthor Commented:
Thanks for your help!
Thank you much.   : )
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