Finding a Serial Device's COM Port in Windows
When a serial port device - or a device whose driver creates a virtual serial port - is connected to your PC, Windows assigns it a COM port - a number between 1 and 255. This assignment is usually persistent between reboots of Windows, but some Windows Updates may change it; when that happens, update whichever application was configured to utilize the previous COM port number to specify the newly-assigned COM port number.
To determine a device's COM port,
- disconnect the device from your PC
in the Windows Control Panel, open the Device Manager; shortcut: press your keyboard's Windows and X keys, and select Device Manager from the popup window.
in the Device Manager, expand the Ports (COM & LPT) section
make a screen shot of the Device Manager window that shows all COM ports, and paste it into the Windows Paint application
close the Device Manager
- connect the device to your PC
open the Device Manager again, and expand the Ports (COM & LPT) section
compare the COM ports shown in the Device Manager with those shown in the screen shot created in step 4 above; the new COM port shown in the Device Manager is what's been assigned to your device