How to change the COM port for a USB Serial adapter on Windows 7

Start by going to the Device Manager. Once there do the following:
Expand the Ports ‘(COM& LPT)’

You should be looking at something like this:

As you can see Windows has set the port to COM10. However many legacy applications expect the port to be between 1-4. Let’s change that:
Right click on the device and click on ‘Properties’.

Click on ‘Port Settings’. Then click on ‘Advanced…’.

Once you’re in ‘Advanced Settings for COM10’ on the bottom you can see the ‘COM Port Number: COM10’. Click on that to change it to the lowest possible number (between 1-4).

Then click ‘OK’ on all open Property Windows.
Now the device should look like this:

53 comments on “How to change the COM port for a USB Serial adapter on Windows 7”

  1. Philmore Sydney Reply

    Just what to say thanks. This website has been very useful in assisting me in getting my usb to serial adapter to work. On my computer however there are no serial ports but when I follow the steps as above to change the com port when the usb to serial is plugged in quite a few of the ports in the drop down list has the status ‘in use’ next to them. Can you tell me the reason for this?


      • laserman Reply

        I found a code that allows you to remove old associations to COM Ports. You can then plug your adapter in and then associate it with the COM Port you need.

        1. Start, All Programs, Accessories, Right-click “Command Prompt” in Accessories and choose “Run as Administrator”
        2. Enter “set devmgr_show_nonpresent_devices=1″ – without the quotes obviously
        3. Enter “start devmgmt.msc”
        4. In the box that opens, select “Show hidden devices” in the ‘view’ menu.

        Now if you expand the section on COM ports, all the COM ports that have ever
        been created will be displayed, the non present ones being in grey. You can
        uninstall away anything that you don’t want (right click, select uninstall).

        • Richard Z Reply

          THANK YOU! I’ve tried 3 devices and about 5 hours trying to download track data from a Garmin GPSMap 76 onto a windows 8 PC using a USB to Serial adaptor. Nothing worked, I was just about to give up when I found your guidance to clear out the old com ports. That did the trick, and the Plugable USB-Serial adaptor finally worked. You saved a PC from taking a short trip across the room in frustration!

  2. Canton Reply

    Thanks a lot for the helpful article. If you don’t mind though, I’d appreciate you’re help, as I’m a bit stuck. When I go to the “properties” dialog for my USB to Serial Port, there is no tab for “port settings.” The tab does appear in the properties dialog of other COM ports though, just not the USB to Serial port. I’ve tried updating the driver, to no avail.

    Any help would be much appreciated!

    • Bernie Thompson Bernie Thompson Reply

      Hi Canton – Can you say what brand of adapter (and if not Plugable, what chipset / driver), and what OS you’re on. Thanks!

  3. matt Reply

    There is no tab for port settings in windows 7 home. Do u know how to change port settings in windows 7 home?

    • Jeff Everett Jeff Everett Reply

      Hi Matt-

      Sorry to hear you’re not seeing the port settings tab, and the delay in getting back to you.

      Our screenshots for this article were done on Windows 7 Home, and the user interface is the exact same on Pro and Ultimate just for the record.

      We’re happy to help if you’re still stuck on this and want to provide a little more info: are you seeing the “Prolific USB-Serial Comm Port” device under device manager, or something else?

      Jeff Everett
      MCITP Enterprise Support Tech

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  5. ray Reply

    I also have the problem where the Prolific USB to serial is installed on com11 and the “advanced” button leads to anohter screen, but there is no provision for changing com port there. Might be IT department blocks that on company PC. I blame the device driver installation software -it SHOULD show defaults and ASK the user if they want to make changes before installing. No nothings can just push the button to install defaults, those of use who know what settings we need could then get it right.

  6. Brad Fluharty Reply

    I just received my Plugable USB to RS-232 DB9 Serial Adapter, and after downloading and installing the updated drivers and tweaking the Com port, was able to use my Icom PCR-1000 for the first time in 6 or 7 years. Receiver software still telling my that it cannot find the port, but it seems to be fully functional. Brad

  7. Steve Reply

    Is there any way to make sure that Windows 7 does NOT swap the port setting once they are set using the above method?

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  9. Ganesha.B.S Reply

    How can I open the port in windows 7 and send commands to that port also get acknowledgement?

  10. Gellan Reply

    thank you so much. I wanted to change the port number of my arduino, but couldn’t find a way to do so. this is the one and only method which worked for me. thanks again for sharing.

  11. Gerry Reply

    none of that worked for me . I am trying to down load a game & it keeps giving me errors when I try to change the port there is nothing there.

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  13. Ian Millard Reply

    Suppose You’re using a modern computer, and there is no device entry for Ports (COM & LPT) because the computer only has USB Ports.
    Then what?

    • Bernie Thompson Bernie Thompson Reply

      Thanks for asking. All modern OSes support virtual COM ports. That’s the mechanism the Bluetooth support in Windows and OS X is using.

  14. Sam Ford Reply

    Hi Bernie – I’m not sure if your postings on this topic has closed.

    I had an “Ham” HF radio connected to a desktop XP and a logging program via RS-232. As I changed bands on the radio, the log program would follow, recording time and date and the frequency of operation. Then, the PC was struck by lightning and I got another PC with new motherboard running Windows 7.

    I now have a radio that runs a USB cable that controls a Contest Logging program However when using an RS232 cable to control my normal logging for contacts, the program does not see the radio or the cable.

    I have tried changing the port numbers but the program still does not see the radio. The two existing ports are 1 and 3 both with Nuvoton Drivers. I tried deleting them but then can not create a new COM1. With the drivers back into the PC, I tried using COM3 for the Ham Logging program but there is still no ‘comms’ between the radio and PC.

    Please HELP !!

    • Jeanie Reply

      Hi Sam, Did you ever get this issue fixed? My father is having the same issue with a logging program and an Elecraft K3. Any help would be appreciated!

      • David Roberts David Roberts Reply

        HI Jeanie and Sam, Thank you for posting. Could you please let me know what device you are connecting to and what the program is that is communicating? It would probably be best to email me directly at Thanks!

      • Sam Ford Reply

        Hi Jeanie

        I’m a complete computer illiterate !! Still not sorted yet. I used to run Swisslog with my TS-2000S using a serial cable. A few months ago, I acquired a TS-590S after selling the TS-2000., I entered a small contest and had N1MM installed using a USB cable. The RS-232 port was used to control the Experk 1K-FA linear. During the contest, N1MM and the linear worked fine.

        After the contest, I tried running SwissLog but the program could not see the COM port. Reading user comments that N1MM and any logging program can not run together, I removed N1MM although they were on different COM ports Now, I keep getting a message that the Com port I am setting up for Swisslog is being used by another device although there are no other devices connected to the PC. I’ve tried changing the Start and Stop bits and tried various combinations and getting more frustrated !

        I trust that your dad will have better luck


  15. Ohnomagicsmoke Reply

    I’ve got a curly one, I’m running PLC’s and simulators through a USB serial converter however every time a new windows session is started some terminals forget their com numbers and I have to reassign them, with close to 100 work stations this is tiresome do you know what the underlying issue is?

    • David Roberts David Roberts Reply

      Thank you for posting your question. What software are you using on the workstations to connect to the PLC’s and simulators? I’m assuming the COM port itself isn’t changing, just the setting in the terminal software.

  16. Pauline Chang Reply

    I am trying to use two 485 Ports at the same time. It looks like when I open the second port, the first connection seems to be disconnected automatically. Is there any way to open/ use two ports at the same time?

  17. terrence m Reply

    Im getting error 10 device not started when connecting the serial to usb cable. Any advice ?.

  18. Mauricio A Reply

    I am trying to use two COM Ports at the same time. It looks like when I open the second port, the first connection seems to be disconnected automatically. Is there any way to use two ports at the same time?

  19. Ted Reply

    Hi! Thank you very much!
    Question: How can I add a port (com)?! I ‘ve got jut one port (for a printer) or can I change it in order to use it for another apparatus (a sat receiver)?
    Thanks.. Regards

  20. sarathpradeep Reply

    my pc -device manager not showing-any” PORT(COM&LPT)”
    how to get it back.what will be the reason for that.

    • David Roberts David Roberts Reply

      Thanks for posting! If this isn’t showing in Device Manager, it probably means that the driver for the adapter is not working properly or hasn’t been installed. If you have a Plugable USB – RS-232 adapter, please contact us at and we can help troubleshoot this. Thanks!

  21. Paul Aeberli Reply

    Hi, I am trying to connect a UT61B multimeter to my dell laptop win7 home via a usb to serial cable. They do not specify one.The meter comes with a female 9 pin connector which works fine when connected to an older WXP desktop unit with traditional com ports.. I borrowed a Prolific (green) cable to try it on the Dell laptop; loaded the software and can see the cable identified in the Device Manager; set the com port to 1 as required by the meter, but no data is transferred from the meter.
    The local computer shop says that the BIOS needs to be set up for the USB ports to be seen as COM ports, but the Dell BIOS has nothing that appears to affect this. I believe it’s a hardware problem, maybe a bad green cable. Any comments?

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