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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallWindows 11 does not have a separate Settings page for adding COM ports. A COM port normally appears when Windows detects a built-in serial interface, USB-to-serial adapter, Bluetooth serial device, or virtual serial-port driver.
If the hardware is already connected but the port is disabled or missing, use Device Manager. If no physical or virtual serial hardware exists, Device Manager cannot create a working COM port by itself—you must connect an adapter or install software that provides a virtual port.
What you need before adding a COM port
For a physical port, connect the serial device first. This might be a USB-to-RS-232 adapter, USB-to-TTL adapter, industrial controller, or another peripheral that uses a serial connection.
Use a driver intended for your exact adapter and Windows 11 where possible. Many adapters use chips from FTDI, Prolific, Silicon Labs, or WCH, and the wrong driver can produce a yellow warning icon or prevent the port from appearing at all.
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How to add or enable a COM port in Windows 11
- Connect the serial device or USB-to-serial adapter to the computer.
- Select Start, type Device Manager, and open Device Manager.
- Expand Ports (COM & LPT).
- Look for an entry such as USB-SERIAL CH340 (COM3), USB Serial Port (COM4), or Communications Port (COM1).
- If the entry is disabled, right-click it, select Enable device, and follow the wizard.
- If the adapter is connected but no new entry appears, select Action → Scan for hardware changes.
The number in parentheses—for example, COM4—is the port name applications use. Enabling the device does not change that number.
If Ports (COM & LPT) is missing
Device Manager may hide the category when Windows has not detected any serial hardware. Try these checks:
- In Device Manager, select View → Show hidden devices. This can reveal an adapter previously installed but not currently connected.
- Unplug the USB adapter, wait a few seconds, and connect it to another USB port.
- Return to Device Manager and select Action → Scan for hardware changes.
- Check Other devices or Universal Serial Bus controllers for an unidentified device with a yellow warning icon.
- Install the driver supplied by the adapter manufacturer, then restart Windows if requested.
A greyed-out entry under Ports (COM & LPT) usually represents an installed device that is not connected now. It does not prove that the physical port is currently available.
Install a missing COM-port driver
If Device Manager lists the adapter but does not assign it a COM number, open its properties and read the error shown under Device status:
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- Double-click the device, or right-click it and select Properties.
- Read the message in the Device status box on the General tab.
- For Code 28, right-click the device, select Uninstall device, then choose Action → Scan for hardware changes. Install the manufacturer’s driver if Windows asks for one.
- For Code 31, use the device’s context menu and select Update driver. If Windows cannot find a suitable driver, download the Windows driver from the hardware manufacturer.
- For Code 32, uninstall the device and select Action → Scan for hardware changes to reinstall it.
Do not rely only on a generic driver when the adapter manufacturer supplies a specific one. Some inexpensive adapters use incompatible or counterfeit chipsets, and installing a driver for a similar-looking adapter may make the problem worse.
Common Device Manager errors affecting COM ports
| Code | Meaning | What to do |
|---|---|---|
| 22 | The device was disabled. | Select the device, then choose Action → Enable device. |
| 28 | The driver is not installed. | Uninstall the device, scan for hardware changes, and install the manufacturer’s driver. |
| 29 | Firmware did not provide the required resources. | Enable the relevant serial hardware in the computer’s BIOS or UEFI, following the manufacturer’s instructions. |
| 31 | Windows cannot load the required driver. | Try Update driver, then install the manufacturer’s driver if necessary. |
| 41 | Windows loaded the driver but cannot find the hardware. | Reconnect the device, reinstall its driver, and scan for hardware changes. |
| 42 | Windows detected a duplicate device. | Restart Windows, then reconnect the adapter. |
| 43 | The device reported a problem and Windows stopped it. | Check the manufacturer’s diagnostics and reinstall the driver. |
| 45 | The previously installed device is not connected. | Reconnect the USB-to-serial adapter or other serial hardware. |
To restart, select Start → Power → Restart. A restart can be necessary after removing a driver or when Windows reports that a driver is still in use.
How to change the COM port number
Adding or enabling a port does not renumber it. If an application requires a particular number, open the port’s properties and look for the port-number setting under the device’s advanced port settings. The exact labels and available numbers depend on the driver.
Do not change the number while another application is using the port. Close terminal programs, flashing tools, and device-management software first. Also avoid assigning a number already used by another active device.
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If the adapter is used by a program that remembers the old number, either select the new COM number inside that program or return the adapter to its previous number.
Can Windows create a COM port without hardware?
Not through Device Manager alone. Device Manager can enable, disable, remove, reinstall, and rescan devices that Windows knows about. It does not create a functional serial interface from nothing.
For a virtual COM port, install a trusted application or driver that specifically provides one. Virtual-port software is commonly used by development tools, modem emulators, Bluetooth integrations, and industrial-control software. Follow that product’s installation instructions rather than manually creating an arbitrary Device Manager entry.
What the old hidden-device command means
Older guides often recommend this Command Prompt command:
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set devmgr_show_nonpresent_devices=1That is not the normal Windows 11 method for showing disconnected devices. In Windows 11, open Device Manager and select View → Show hidden devices.
Quick verification from a terminal
After the port appears in Device Manager, you can list detected serial devices from PowerShell:
Get-CimInstance Win32_SerialPort | Select-Object DeviceID, Name, StatusA result such as COM4 confirms that Windows has registered the port. This does not prove that the connected equipment is communicating correctly; baud rate, parity, stop bits, wiring, and the application’s port settings must also match.
FAQ
Where are COM ports in Windows 11?
Open Start, search for Device Manager, open it, and expand Ports (COM & LPT). Windows 11 does not provide a separate COM-port switch in the Settings app.
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Why is my COM port not showing?
Reconnect the adapter, try another USB port, select View → Show hidden devices, and then select Action → Scan for hardware changes. If the device appears under Other devices with a warning icon, install its manufacturer-provided driver.
How do I enable a disabled COM port?
In Device Manager, expand Ports (COM & LPT), select the disabled device, choose Action → Enable device, and complete the wizard.
Does enabling a COM port change COM3 to another number?
No. Enabling the device restores it to operation but does not change its assigned COM number.
Can I add a COM port if I do not have a serial device?
Device Manager cannot create a working COM port without hardware or a virtual COM-port driver. Connect a serial adapter or install trusted software that specifically provides a virtual serial interface.
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Is set devmgr_show_nonpresent_devices=1 required in Windows 11?
No. Use Device Manager’s View → Show hidden devices option to display installed devices that are not currently connected.
The Bottom Line
To add a COM port in Windows 11, connect the serial hardware, open Device Manager, and check Ports (COM & LPT). Enable the device if it is disabled, use Action → Scan for hardware changes if it is missing, and install the correct manufacturer driver for any error code. If no hardware exists, you need a virtual COM-port driver—not a Settings switch.
Microsoft’s Device Manager error-code guidance covers these enable, rescan, driver, and troubleshooting steps.
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