com port assignment windows 10

How to Enable COM Port in Windows 10: Step-by-Step Guide

Enabling COM Port in Windows 10 might sound technical, but it’s actually pretty straightforward. By following some simple steps, you can make sure your computer recognizes and uses COM ports effectively. Whether you’re setting up a new piece of hardware, troubleshooting a connection, or tweaking settings for an application, enabling COM ports is a critical skill to have.

How to Enable COM Port in Windows 10

In the following steps, we’ll go through the process of enabling a COM port on a Windows 10 machine. This will involve accessing the Device Manager, modifying port settings, and ensuring your system recognizes the port.

Step 1: Open the Device Manager

First, right-click on the Start button and select "Device Manager" from the context menu.

Device Manager is your go-to tool for managing hardware and drivers on your computer. It displays all the connected devices and allows you to configure them.

Step 2: Expand the Ports Section

Once in Device Manager, find the "Ports (COM & LPT)" section and click the small arrow next to it.

This section shows you all the available COM ports. If you don’t see it, it means no COM ports are currently recognized by your system.

Step 3: Right-click on a COM Port

Right-click on any of the listed COM ports and select "Properties" from the dropdown menu.

The Properties window gives you detailed information about the selected port and allows you to adjust its settings.

Step 4: Navigate to Port Settings

In the Properties window, go to the "Port Settings" tab and click on "Advanced".

Here you can change various settings related to the COM port, such as baud rate, data bits, and more.

Step 5: Change the COM Port Number

In the Advanced Settings, you can change the COM Port number if needed. Click "OK" to save the changes.

Changing the port number can help resolve conflicts with other devices and ensure smooth operation.

Step 6: Confirm and Close

After making your changes, click "OK" to close the Properties window and then close Device Manager.

Your changes will be saved, and the COM port should now be enabled and ready for use.

After completing these steps, your COM port will be enabled, and your computer should recognize it without any issues. This means you can now connect external devices that use COM ports and configure them as needed.

Tips for Enabling COM Port in Windows 10

• Check for Updates: Make sure your Windows 10 system is up-to-date to avoid compatibility issues with COM ports.
• Use the Correct Drivers: Ensure you have the right drivers installed for your hardware that uses COM ports.
• Troubleshooting: If the port doesn’t show up, try restarting your computer or checking the hardware connections.
• Port Conflicts: If you experience conflicts, try changing the COM port number in the Advanced settings.
• Backup Settings: Keep a record of your port settings before making changes, so you can revert if needed.

Frequently Asked Questions

What is a com port.

A COM port, or communication port, is a serial port that allows for communication between the computer and external devices.

Why don’t I see any COM ports in Device Manager?

If no COM ports are visible, it could be due to a lack of relevant drivers or that no COM port hardware is currently connected.

Can I use multiple COM ports at once?

Yes, you can use multiple COM ports simultaneously, but ensure there are no conflicts in port numbers.

How do I know which COM port my device is using?

You can check the COM port assignment in Device Manager under the "Ports (COM & LPT)" section.

What do I do if my COM port isn’t working?

Check the device’s drivers, ensure no port conflicts, and verify that the hardware is properly connected and functioning.

Step-by-Step Summary

• Right-click Start button, select "Device Manager".
• Expand "Ports (COM & LPT)" section.
• Right-click on a COM port, select "Properties".
• Go to "Port Settings" tab, click "Advanced".
• Change COM Port number, click "OK".
• Confirm changes and close Device Manager.

Enabling a COM port in Windows 10 is easier than it seems. By following the steps outlined in this guide, you can quickly get your COM port up and running. This process involves accessing the Device Manager, tweaking settings, and ensuring the port is recognized by your system.

So, why wait? Get started right away and make the most of your hardware! For further reading, you can explore more about device management in Windows 10 or delve into troubleshooting common COM port issues. Now that you know how to enable COM port in Windows 10, you’re well-equipped to handle any related challenges that come your way.

Matt Jacobs has been working as an IT consultant for small businesses since receiving his Master’s degree in 2003. While he still does some consulting work, his primary focus now is on creating technology support content for SupportYourTech.com.

His work can be found on many websites and focuses on topics such as Microsoft Office, Apple devices, Android devices, Photoshop, and more.

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How to change the COM port for a USB Serial adapter on Windows 7, 8, 8.1, and 10

Originally authored by: Bernie Thompson, July 4, 2011

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:

COM port in Windows 10 & 11: fix any COM port-related issues in 2 easy ways

In this article, we are going to discuss two ways to resolve the problem of the lack of COM ports on computers running the Windows 10 and/or 11 operating system . Windows 10 and/or 11 COM port issues plague many users whose computers have been designed without the inclusion of any serial interfaces. The absence of physical COM ports can hinder a user’s ability to make use of computing peripherals that transmit their data serially.

The way to resolve this issue is through the use of Windows virtual serial ports. It can be very frustrating to query your Device Manager with the expectation of finding COM ports only to find that they are not present. We are going to show you two different methods you can use to add COM ports to Windows 10 and Windows 11 . One is a procedure that employs the native functionality built into the operating system and the other uses third-party software.

The Problem: Windows 10 COM ports not showing in device manager

Finding virtual COM port in Windows 10 causes issues for some users. Individuals navigate to their Device Manager, anticipating that they’ll find virtual COM port drivers previously loaded on their machine.

However, when they open their Device Manager, they’re perplexed and frustrated once they realize these COM ports aren’t listed.

The reason being, said serial port option may not be available because of the Windows 10 update installation.

The update could impact virtual serial port drivers ability to load specific devices by default. This creates a major problem for those using such (seemingly) incompatible devices.

There are several solutions. One option is to find com port Windows 10 by following the steps below:

Step 1: Open the Device Manager.

Step 2: From the menu bar, click View.

Step 3: Choose “Show hidden devices”.

Step 4: From the list of hidden devices, find the Ports (COM & LPT).

Step 5: Expand the same menu (“+”) to check for the missing COM ports.

If you can't find com ports this way, the next step is investigating how it can be done with Electronic Team’s Virtual Serial Port Driver for Windows 10 virtual serial ports.

To ensure the easiest solution possible, see our step-by-step procedure below. A process that can help users eliminate problems with their COM ports on Windows 10 in as few as three clicks.

Keep reading to learn how easy and convenient it is to use this Windows 10 virtual COM port driver.

Add COM port Windows 10 with Virtual COM Port Driver

When the COM and LPT ports do not appear in your Windows 10 Device Manager your ability to perform your work is negatively impacted. There is a way to resolve this annoying problem in a manner that will prevent it from recurring. The solution is to install the aforementioned Virtual COM Port Driver from Electronic Team . This application allows the creation of an unlimited number of virtual serial port pairs. The virtual COM port pairs employ a virtual null-modem connection to enable communication with each other.

• Virtual COM Port Driver

Virtual Serial Port Driver

Users engaged in the practice of developing and testing serial applications and hardware will benefit from the configuration options that are possible through the use of Virtual Serial Port Driver. One example is the ability to allow two applications to share data via virtual serial ports. Connecting the apps with a pair of virtual COM ports lets the data written by one program be immediately made available to the other program. This can save significant time and effort when debugging and testing serial apps and devices.

Step-by-step guide to add virtual COM port Windows 10:

Create virtual COM ports in Windows 10 with USB Serial Converters

Most often, virtual COM ports in Windows 10 install automatically when a user connects a converter to a computer with internet access. Unfortunately, there are Serial Converter device drivers that won’t automatically install on certain operating systems.

This is not a major issue, as users can simply install the drivers utilizing the disk that comes with their specific Serial Converter.

Follow the instructions below to install Serial Converter device drivers from a disk:

• After inserting the CD into the disk drive, connect the USB Serial Converter to an open USB port.
• The “ Found New Hardware Wizard ” should run automatically, and will guide users through the remaining installation.
• Once prompted to connect with Windows Updates (which will ask to search for available drivers), choose the “ No, not at this time ” option.
• Follow all instructions to complete driver installation using the provided CD.
• ○ Under “Ports (COM & LPT)”, the device will be labeled as “ USB Serial Port (COMx) ”

• If drivers haven’t been installed correctly, a yellow exclamation icon is displayed under the “Ports (COM & LPT)” or “USB Serial Bus Controllers” menu.
• To fix any issues with installation: right-click the yellow exclamation icon, click “ Update Driver ”, and then search for the necessary driver (located on the disk provided with the USB Serial Converter).

How to change COM port settings in Windows 10

Some software applications are designed to only operate with designated serial ports. If you need to work with this kind of program, you may need to know how to find port numbers in Windows 10 so you can modify them if necessary.

In many cases when working with older devices or applications, you will be called upon to change COM port numbers to successfully operate the programs and peripherals. Some legacy equipment is only capable of working with specifically named serial ports.

The following procedure allows Windows users to change the COM port number for any attached device.

Just follow these simple steps on a Windows 10 machine to change the default COM port number.

• The Advanced Settings window is where you perform the number reassignment. You select an available port number from the list presented in the lower-left of the window. In our example, we are updating the device’s number from COM 3 to COM 5.
• Save the settings by clicking the OK button. This will close the open windows. The new number may not be assigned until the device is removed and reconnected to the computer.

Tip: Here is what you can try if COM ports are not showing in Device Manager:

• Open Control Panel.
• Search for “device” using the box in the top-right corner and select Device Manager from the results.

How to assign a COM port to a USB device Windows 10?

There are multiple scenarios in which you may need to assign a COM port to a USB device on your Windows 10 computer. Some devices need to have a COM port identifier that falls within a certain range, say between COM1 and COM4. Windows may have assigned a different identifier to the port which you will be required to modify. It’s a relatively simple procedure to perform.

Here is how to assign a COM port to a USB device Windows 10:

• Open the Windows Device Manager.
• Click on the Ports (COM & LPT) to expand the selection. You will see the ports currently in use along with their designated port identifier.

• Click on Port Settings and then click the Advanced button .
• Locate the COM Port Number at the lower left of the Advanced Settings window.
• Click the Com Port Number to change the currently assigned port identifier. Select the COM port identifier that you wish to assign to the USB device attached to the port.
• Click OK on all open Property windows.

Following these steps will enable you to change the COM port identifier for USB devices attached to your Windows 10 machine.

How to Reset com ports Windows 10

COM port (Communication port) is the title given to the port serial interface that’s located in a common (IBM compatible) computer.

There are occasions when computers offer users one or two physical COM ports (RS-232), but today's models usually lack these physical COM ports. It should be known that COM ports don’t always refer to physical ports. Virtual ports are available as well. These ports are developed when a USB-to-UART adapter is used—most often utilized by FTDI and Croduino.

See below for multiple examples of such devices (AKA cell phones, USB modems, RFID readers, card readers, etc.)

In each instance where Windows registers a new device (one which possesses a new ID), Windows connects that device to an empty port, from COM 1 port if you didn’t have any connections before, then (COM2, COM3, COM4, ​​etc.—from 1 to 255).

Additionally, every port is exclusively assigned to a single device, remaining occupied (Windows displays the COM port as “in use”) even when the device isn’t connected anymore.

For a majority of the time, this isn’t an issue unless users attempt to run certain legacy software (software that struggles to function with COM-ports higher than 9.)

One example is when an app functions effectively with COM1 to 9, but fails if no unoccupied COM ports below COM10 are available.

Another problem can occur when certain devices require far too many COM ports to function.

Specific adapters could reserve up to 30 (or more) COM ports. This situation means users are forced to delete COM ports being used in Windows—or switch a currently occupied COM port to a different device.

The tutorial below will explain how to clear currently occupied COM ports, as well as how to disable the numbering of new ports.

• Step 1: Hit Win+R (write regedit then click Enter).
• Step 2: Search through folders: HKEY_LOCAL_MACHINE\SYSTEM\CurrentConstrolSet\Control\COM Name Arbiter .

Note: This opens a window displaying port addresses.

• Step 4: Enter all zeros to reset.

What is USB serial port driver FTDI

Virtual COM port (VCP) drivers make USB devices appear as additional COM ports that the PC can access. USB devices can be accessed by application software similarly to how it would access standard COM ports.

Future Technology Devices International Limited’s software is offered “as is”. Any and all described (or implied) warranties (including, but not limited to, implied warranties of merchantability and fitness for a particular purpose) are disclaimed.

In no event shall Future Technology Devices International Limited be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused, and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.

FTDI drivers can be used only in conjunction with products based on FTDI parts.

Frequently Asked Questions

How to find device manager on windows 10.

• Using Windows Search The easiest way is to use the default Windows search bar located next to the Start Menu on the toolbar. Simply start typing “Device Manager” into the search field and it will be located for you with an easy “Open” link to access it.
• Open the Control Panel on your computer.
• Locate the “View By” option in the top right of the “Control Panel” screen.
• Select “Large icons” or “Small icons” according to your preference.
• “Device Manager” will be listed - all icons are ordered alphabetically in ascending order.
• From the WinX menu There are two ways to access the WinX menu. Either right-click on the “Start” menu or you can press Windows + X keys on the keyboard at the same time. Device Manager will be listed as an option in the menu that appears.
• devmgmt.msc
• mmc devmgmt.msc
• control hdwwiz.cpl
• From the Computer Management Console You can access the Device Manager from the Computer Management Console. Device Manager will be listed in the left panel under System Tools.

How to find COM port number on Windows 10?

• If the details of your COM ports are not visible in the Device Manager, open Device Manager and click on “Action” from the menu bar.
• Select the “Add legacy hardware” option, then click Next.
• Choose the “Install the hardware that I manually select from a list (Advanced)” option, and click Next.
• When complete, the “Ports (COM & LPT)” group will be listed in the Device Manager. Expand the group to view your device. The port along with the port number ie. Communications Port (COM4) will be displayed accordingly.

How to install a serial port driver?

• Download Virtual Serial Port Driver
• Double click to launch the application. If you see a User Account Control message, click “Yes” to allow the application to be installed.
• Follow the steps in the installation wizard. Read and accept the License Agreement, and click Next to continue.

Can't open the serial(com) port, What to do?

• Number 1: Connection to com1 Windows 10, com3 wouldn’t open. This issue sometimes occurs if users lack the required drivers. Solve this problem by updating the serial port driver, then verify the issue was resolved.
• Number 2: Putty can’t open Windows 10 serial port. This can happen because of certain Windows services. Resolve this issue by disabling these services.
• Number 3: Access to the serial interface com1 cannot be opened – This problem may occur due to problems with the serial interface. Resolve the problem by temporarily disabling the serial port
• Number 4: Com ports can’t open win error code 5, 123, 32. These are very common issues that often occur with a serial port Resolve most of these problems with one of our solutions

• COM Port on Windows 10

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Configuration of COM ports

• 2 contributors

A COM port is a type of serial port that complies with the following additional requirements:

You access the COM port through an instance of the COM port device interface class. The GUID for this class is GUID_DEVINTERFACE_COMPORT, which is defined in Ntddser.h.

You operate the COM port by using the 16550 UART-compatible interface that is defined in Ntddser.h.

To ensure compatibility with most applications that access COM ports, you should assign a symbolic link name that uses the standard naming convention COM<n> , where <n> is the COM port number (for example, COM1). If you use a COM<n> name, you must obtain the COM port number <n> from the COM port database . COM port numbers should only be used with COM<n> names.

By default, the combined operation of the class installer for the Ports device setup class and the Serial function driver configure a device as a COM port.

For information about how the Ports class installer and Serial function driver create a COM port device interface for a COM port, see External naming of COM ports .

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How To Add COM Ports Missing In Device Manager

COM ports are common components of Device Manager. Windows users can see them easily by opening the Device Manager. However, problems may occur, causing the COM ports lost from Device Manager. If you are encountering this, please read the methods mentioned below to try to fix the problem yourself.

Windows 10 COM Ports Device Manager

COM stands for Communication port and it is actually the original name of the serial port interface. The COM can be used to refer both physical ports and emulated ports, which are created via the Bluetooth or USB-to-serial adapters. Well, the COM ports missing in Device Manager problem happens now and then.

How to Access Windows 10 Device Manager Ports

• Right click on This PC icon on the desktop.
• Choose Manage from the context menu.
• Select Device Manager under System Tools. (You can also press Start + X directly to select Device Manager .)
• Choose View from the menu bar.
• Choose Show hidden devices from the submenu.
• Locate Ports (COM & LPT) from the list in the right pane.
• Expand it to find Communications Port (COM) .

MiniTool Software could help you recover data from hard disk, USB flash drive, and other external storage. If you find the USB ports not showing in Device Manager Windows 10, please read this to know how to fix USB not recognized issue.

Various solutions are provided for you to fix the USB flash drive not recognized error and recover data from the inaccessible flash drive.

How to Assign a COM Port to USB Windows 10 Device Manager

Sometimes, you may need to assign a COM port to a USB device connected to your Windows 10 computer. Here’s how to do:

• Open Windows Device Manager.
• Click to expand Ports (COM & LPT) .
• Right click on the target USB device.
• Select Properties .
• Shift to Port Settings .
• Click Advanced .
• Select a proper COM port identifier from the drop-down menu of COM Port Number .
• Click OK to confirm.

COM Ports Missing in Device Manager

However, there are many peoples said they can’t find ports in Device Manager and they desperately need a solution to it.

COM Ports Not Showing in Device Manager: Ture Cases

One: Com Port is Missing / Ports Option Not Available In Device Manager.

My com port is missing. And the ports option is not available in Device Manager. I’m able to perfectly connect and use my phone/modem with the computer. I had gone through several discussions about same topic here in answers.microsoft.com to no avail. How do I enable it, or can you provide a link where I can download this com driver for windows 10? Thanks. – posted by etwdensegen sprechen in Microsoft Forum

Two: No Ports shown in Device Manager (even hidden) Win 7 Pro 64 bit.

I can’t get an external modem to work (even though it shows in devices and printers window. I can’t get a USB-serial port converter to work either. It would be helpful if I had info from the device manager window but nothing show up, even though I have turned on the show hidden devices. Any ideas? Thanks. – asked Paul Saacke in Microsoft Forum

Three: COM PORT is disappeared in Device Manager.

When I opened device manager at that time I found that, portable devices COM port option disappeared from device manager. What should I have to do to resolve this issue? – said SAY014 in HP Forum

So how to fix the problem and find back your Windows 10 COM ports? Please keep reading!

How Do I Add a COM Port to Device Manager

Some users complained that their Widows 10 COM ports disappeared from Device Manager after they have upgraded their Windows platforms. Whatever the cause, the users’ primary concern is how to restore missing COM ports. That’s what I’m going to talk in this section.

[SOLVED] Files Disappear From PC? Try These Useful Solutions!

Method 1: Show hidden devices.

As I have mentioned at the beginning of this article, users can’t see the COM ports directly. Instead, they need to open Device Manager -> select View tab -> choose Show hidden devices . After that, they’ll see the Ports (COM & LPT) option and they only need to expand it to fins COM ports.

Method 2: add COM ports manually.

• Open Device Manager on your Windows 10 computer.
• Click on the Action option from menu bar.
• Choose Add legacy hardware from the submenu to open the Add Hardware window.
• Click on the Next button to move on.
• Check Install the hardware that I manually select from a list (Advanced) and press Next .
• Select Ports (COM & LPT) from the given list and press the Next  button.
• Choose Standard port types option or the manufacturer for the ports; then, click Next .
• Click on the Finish button to complete.

Method 3: update the motherboard drivers.

If the motherboard drivers are too outdated, they will also lead to COM ports missing in Device Manager. Therefore, you are advised to update your motherboard drivers manually and see whether it works.

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Change COM Port Number programmatically

In Device Manager, I can right click on a serial device, navigate to the Port Settings tab, click Advanced, and change the COM Port Number via a drop-down menu.

I need to automate this step across a large number of PCs. Is there a way to script this process, or to do it programmatically?

• serial-port

• Are they all the same version of Windows? –  End Antisemitic Hate Commented Dec 11, 2014 at 6:46
• They are not - could be WinXP, Win7, or Win8. Having said that, I'll happily accept a solution that only works on one (better than nothing!) –  Matthew King Commented Dec 11, 2014 at 6:51
• Hmmm....curious what is the specific application for this process? –  mdpc Commented Dec 11, 2014 at 7:22

This question is probably best asked on stack overflow . That said, take a look at ComDBReleasePort and ComDBClaimPort in the COM Port Database . However, changing COM port assignments programmaticly is not exactly considered a best practice. For example, what happens if two more more concurrent applications are fighting to get the same COM assignment?

Windows dynamically assigns COM port numbers for a good reason. Ideally, your application should be written so that it searches for the specific COM port it needs. This can be done via polling or by using the Windows Management Interface (WMI) .

If you're referencing some application that someone else wrote, and you're just stuck with someone else's program design (or lack thereof), then you may want to consider adding a batch script to modify the registry key under HKLM\Hardware\DEVICEMAP\SERIALCOMM at startup, since the new value(s) are not likely to hold between re-boots.

I don't know how how well this last option would work, but if you're a serious PowerShell or Python user, you could theoretically use either scripting language to directly access the APIs mentioned at the beginning of my response for a one-time COM port re-assignment.

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How to Free (Reset) COM Port in Use in Windows

When you connect a new COM, USB, or Bluetooth device to your computer, Windows assigns the first available free COM port number from 1 to 256 to the device (COM1, COM2, COM3, etc). Even after the device is disconnected, the assigned COM port number is not released and remains reserved for the device (Windows shows it as “in use”). Some legacy apps can only use low COM port numbers from 1 to 9. In order for such an application and device to work properly, you should change the assigned COM port number or completely release the reserved COM ports used by other app.

Note . Virtual COM ports are still widely used in Windows, although modern computers almost never have physical serial COM ports on the motherboard. For example, virtual COM ports are currently used by USB (USB-to-UART, USB-to-COM, USB modem, card/RFID reader) and Bluetooth adapters.

How to Change the COM Port Number in Windows

The administrator can manually change the assigned COM port number for the device using the Device Manager.

• Open the Device Manager (press Win + R and run devmgmt.msc )
• Expand Ports (COM & LPT) ;

These steps won’t help if Windows says you that the COM port you need is already in use. In this case, try to manually reset the used COM port and then reassign it to a new device.

Reset COM Port in Use on Windows

If the device is not currently connected to the computer, you can reset its assigned COM port number.

• Expand the Ports (COM & LPT) section. Disconnected devices have the reserved COM port number in their names and greyed out icons;

• DO NOT check the option “Delete the driver software for this device”;
• Repeat these steps until all grayed-out COM ports are removed;
• Now you can assign a free COM port number to the device you want as described above.

How to Find Which Process is Using the Serial (COM) Port

COM ports are used by devices in Windows in exclusive mode. A COM port cannot be released or deleted if it is being used by another running process. In this case, use the Process Explorer to find out which Windows app is using the COM port.

• Go to the Device Manager , expand Ports (COM & LPT) , right-click on the COM port you want to check, and select Properties ;
• Go to the Details tab, select Service from the Property dropdown list ;

• Download the Process Explorer utility from Microsoft;

• Paste the COM port handle you copied from Device Manager into the Handle or DLL substring search box ( serial in this case) and click Search;

• Then you can reassign the COM port number to another device.

Clear COM Ports Using the COM Name Arbiter

The free third-party tool COM Name Arbiter can be used to release unused COM ports and change assigned port numbers. Download the COM Name Arbiter Tool from the official website and run as an Administrator.

The tool shows list of COM ports with checkmark next to the currently busy ports of connected devices. Press the Remove non-present devices to clear all assigned COM port number reservations.

You can also clear the COM port manually, by unchecking a specific device from the list.

Another handy tool for viewing COM port configuration is COM Port Info . This tool allows you:

• View assigned COM port numbers;
• Safely remove hardware;
• Change and swap COM port numbers;
• Reset USB Ports.

Removing Unused COM Ports via CMD

The built-in PnPUtil tools can be used to list and remove assigned COM port numbers from the command prompt.

List COM port devices:

In this example, the COM3 port is assigned to a MediaTek USB Port device. This device is currently Disconnected .

Copy and paste the Instance ID into the following command to remove this COM device reservation:

Reset COM Ports Reservation via the Registry Editor

The following low-level method of removing all COM port reservations in Windows requires direct modification of the system registry. Windows stores COM port assignments in the registry value of the ComDB parameter under the reg key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter . You can make direct changes to the registry to reset COM port reservations.

Caution . Create a system restore point before making these registry changes.

• Disconnect any peripheral devices from the computer;
• Open the Registry Editor (regedit.exe);
• Go to the reg key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter ;

• Restart your computer. When it boots back, connect all the COM devices in the proper order.

Now you know how to delete COM ports and reassign them to a different device.

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Brian Jackson started this blog in 2011. Brian has a huge passion for WordPress and technology for over a decade. Brian enjoys blogging, movies, and hiking.

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How to Change COM Port on USB Modem

One pesky problem with Windows 10, as well as the earlier versions of the Microsoft Windows operating system, is that the COM port assignments for devices that use them, often change.  In this post, we show how to change COM port number on USB modem back to what it was before. Or, you can do this to changed assigned port number at will to any unused port you desire.

A USB modem for example, may start off being assigned to COM3 when you plug it in right out of the box.  But that assignment can (and often does) change to COM4 or some other COM port, any time the modem is unplugged and reconnected, the computer restarts, a new version of a device driver is installed, a different USB port is used, certain Windows updates are installed, and a myriad of other possible port reassignment triggers.

Of course, when the modem COM port changes, any program that relies on the modem listening on the original COM port, no longer functions correctly.  The solution is to change the modem COM port back to the one it was originally using, and the procedure below demonstrates how to do this.

How to Change COM Port on USB Modem, Windows 10

1. plug usb modem into working usb port on windows 10 computer.

You won’t be able to change its COM port settings if it’s not connected to your machine when you try.

2 . Bring up  Device Manager   Window

You can find Device Manager in Control Panel, or enter the word -Device- into Cortana’s search box.  This brings up a link to -Device Manager- (usually the first one) in the results list.  Tap that link, and you’ll see a screen similar to the shot in the next picture.

3 . Find the Modems Device Group Item to Continue with How to Change COM Port on USB Modem

The purple arrow points at the Modems group in the last picture.

Then, tap / click the downward pointing arrow immediately to the left of that entry.  This expands the Modems device group, as shown in the next picture, revealing any modems currently connected to and operating correctly on your computer.  In this demo, we only have one USB modem connected, as listed.

4. Double Click the Entry for the Modem to Change

In our demo here, we’re changing the COM port for the Agere Systems USB 2.0 Soft Modem.  So, we double click the entry for that modem, and this brought up the Windows 10 device configuration screen for this modem, as shown next.

5. Then, Click / Tap the  Advanced   Tab

The purple arrow points at the Advanced tab in the last picture.  The configuration window then redraws itself to show the advanced configuration options for this particular modem, as shown in the next picture.

6. Tap / click the  Advanced Port Settings   Button to Continue with How to Change COM Port on USB Modem

The purple arrow in the last picture points at the  Advanced Port Settings   button.  Doing so brings up the -Advanced Settings for COMx- window, as shown next.  The actual COM port number that is currently assigned to the modem replaces the x in COMx here.  In our demo here, this window is for COM4.  Thus, we see that our modem is currently assigned to COM4, although we wish to assign it to COM3.

7. Expand the  COM Port Number   Pop-up Combo Box

Do that by tapping / clicking the downward pointing arrow immediately to the right of the port number.  We’ve drawn a purple arrow in the previous picture, pointing at this expander button in the previous picture.  When you expand the list, you get a complete list of available COM ports that this modem may use, as shown in the next picture.

8. Tap / Click the Desired New Port number in the List

You may have to scroll up or down in the list to find the port you want.  In our demo, we’re assigning our modem to COM3.  So we tap COM3 in the list, as shown in the previous picture, pointed at by the purple arrow.  This then collapses the expanded port list back down to a single entry in the -COM Port Number- field, showing the new port number we chose.  We’ve changed our modem to COM3, as shown in the next picture.

9. Tap / Click the OK button on the  Advanced Settings for COMx   Window to Continue with How to Change COM Port on USB Modem

Doing so closes that window, and reveals once again the device configuration window for our modem, as shown next.

10. Press the OK Button on the Device Configuration Screen

This applies the new COM port assignment to the modem, and closes that window, once again revealing the Windows 10 Device Manager window, as shown in the next picture.

11. Exit the  Device Manger Window

Exit either via its file->Exit menu item as shown in the previous picture, or by tapping / clicking its -Close- button, found in the top right corner of the window (the X button).  Your COM port reassignment for the modem is now complete.

With the COM port successfully changed, we recommend that you close and restart any program(s) that use the modem, and, if necessary, change the COM port settings in said program(s) to match the port number we just set up.

12. Done with How to Change COM Port on USB Modem !

Related posts to how to change com port on usb modem .

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Other Posts About Windows 

• Disabling Windows 10 Upgrade Notifications in Earlier Windows Versions
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References for How to Change COM Port on USB Modem

• Change the Modem COM Port, from Verizon Wireless
• How to change the COM port for a USB Serial adapter on Windows 7, 8, 8.1, and 10,  from Pluggable.com

Revision History

• 2019-05-30: Added links and tags.
• 2019-04-27: Added tags.
• 2018-04-18: Revised post title and content for better keyword targeting.
• 2017-12-04: Originally published.

Last Updated on 10 months by Tom Hesley

Windows 10 Top Contributors: neilpzz  -  Ramesh Srinivasan  ✅

October 14, 2024

Windows 10 Top Contributors:

neilpzz  -  Ramesh Srinivasan  ✅

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Knowledge Article

Com port number assignment in windows, question how are com port number assigned by windows answer windows will assign a com port number that is the next free com port in the list. for example, if you attach a jul 9, 2021 knowledge, information, nothing here yet.

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How to change asynchronous serial COM port assignments in Windows Device Manager

Sealevel recommends using the installed COM numbers if at all possible to avoid system conflicts. If you previously installed a USB or PCMCIA serial interface, it will have resources assigned by the operating system. If the device is not currently connected to your computer, these COM assignments will not be apparent and forcing new COM port assignments will create a conflict when the devices are reconnected at a later time.

One scenario where you would have to change the COM port assignments is when your legacy application only works at COM1 through COM4 and the Sealevel serial device you installed comes in at COM5 or higher. Another scenario might occur when you install a multiport serial card and the COM port numbers are not assigned consecutively and you want them to appear consecutive.

In Windows 7, Vista, XP or 2000 operating systems, you can change the COM number assignment using Windows Device Manager.  To change the COM port assignments in Device Manager, follow these basic steps:

1) Click the Start button.

2) Right-click on My Computer.

3) In the fly-out menu, click Manage.

4) In the Computer Management Window, click on Device Manager.

5) In the right-hand pane, expand the Ports (COM & LPT) listing by clicking the “+” symbol.

6) Right-click on the COM number you want to change and select Properties from the fly-out menu.

7) In the Communications Port Properties window, click the Port Settings tab and then click the Advanced button.

8) In the Advanced Settings window, you can select the new COM port number from the drop box (be careful not to select a COM number already in use).

9) Click the OK button to confirm your changes. If Windows detects a conflict, choose another COM port number.

10) Click the OK button to close the Communications Port Properties window.

11) When Device Manager refreshes the hardware list, the COM assignment will reflect your changes. To get Device Manager to refresh the window on Windows XP, you may need to click ‘Action’ in the menu and then click ‘Scan for hardware changes’ in the sub-menu (Note: If ‘Scan for hardware changes’ isn’t listed in the sub-menu, click on the computer name in the right pane and then repeat this step).

Contact our technical support department if you are still experiencing problems with serial COM port assignments.

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