Home > windows > setting ports (com & LPT) remove in use or unistall unused port

setting ports (com & LPT) remove in use or unistall unused port


If you’ve got software that uses a pull down menu to assign a COM port in Windows XP, it may require that the device in question be in a low range, like COM1 – COM4, or COM1 – COM8. I’ve noticed that as I have connected various serial devices to my computer (usually devices that use USB-serial drivers), Windows reserves that port for any time I may re-connect that device in the future. After a while, it’s common to notice that new COM port numbers that are automatically assigned start to creep up into the double digits. You can reassign a COM port to a lower number, but to do that, the port has to be available. If you find that all the lower ports are reported to be ‘in use’, then it may not be possible to do that, which may make it impossible to use the software that has a limit on the COM port number range. In general, to move a COM device to a different COM port number, here are the steps:

1. Right-click on the “My Computer” icon on the Desktop and select Properties.

2. In the window that opens, click on the Hardware Tab and then click on the Device Manager button.

3. From the menu at the top of the window, select View – Show Hidden Devices.

4. Expand the node marked Ports (COM & LPT) and examine the current COM port assignments. One should be listed as the device you want to change.

5. Double-click on the port you want to change. This brings up the Properties dialog.

6. Select the Port Settings Tab and then click on the Advanced button. This brings up the Advanced Settings dialog.

7. Set the COM Port Number to the desired setting. If the port that you want to select is marked as “In Use”, you must free that port – as explained here:

How to remove COM ports that are ‘in use’, but not currently connected to anything:

To release COM ports that Windows XP has reserved from previous installations of COM port drivers that are no longer connected follow the steps below. It’s important to follow the steps exactly, i.e., don’t start the device manager using a method like the one mentioned above, you must launch the device manager from a DOS prompt as shown in Step 3 below for this to work properly.

1. Click Start, point to All Programs, point to Accessories, and then click Command Prompt.

2. At a command prompt, type the following command , and then press ENTER:

set devmgr_show_nonpresent_devices=1

3. Type the following command at command prompt to start the Device Manager, and then press ENTER:

start devmgmt.msc

4. Click View > Show hidden devices. This will display devices that are not connected to your computer but Windows XP still reserves space for them.

5. Go to Ports (COM & LPT) and expand that section.

6. Remove all devices in the list of ports that are grayed out but have a specific COM port number assigned to them. (You can do this by right clicking on the grayed out device and choosing Uninstall and then OK in the dialog box that appears).

7. When you are finished troubleshooting, close the Device Manager.

8. Type exit in the Command Prompt

Categories: windows
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