How to Find the Process Using a Serial Port on Windows

To find the process that is using a serial port on Windows, follow these steps:

Open the Device Manager by right-clicking on the Start button and selecting Device Manager.
Expand the Ports (COM & LPT) section.
Right-click on the serial port and select Properties.
Select the Port Settings tab.
Click on the Advanced button.
In the Advanced Settings window, select the COM Port Number dropdown and note the COM port number.
Open the Command Prompt by pressing the Windows key and typing cmd.
Type the command 'netstat -ano' and press Enter.
Look for the PID (Process ID) column and find the process that is using the COM port number noted earlier.
Note the PID number and open the Task Manager by pressing Ctrl+Shift+Esc.
Click on the Details tab.
Look for the process with the same PID number noted earlier.
Right-click on the process and select End Task to terminate the process.

Note: Make sure to only terminate processes that you are certain are not needed as terminating important processes can cause system instability.