USB to Serial Adaptor - COM Port Numbers

Today’s laptop computers rarely have an RS232 serial port built-in. Most users in the racing industry will need the use of a serial port if they plan to utilize new systems employing a programmable microprocessor. The solution, as most of you already know, is to install a USB to Serial adaptor. Most of these do the job quite well, but can be frustrating to use at times. The majority of the problems I see a user experiencing has to do with not knowing or being able to determine the COM port number assigned to the USB adaptor.

This document gives examples of how to determine the adaptor’s COM number.

To use this document, you must have previously installed the USB adaptor and all drivers or software supplied with the adaptor. With the USB to Serial adaptor plugged into an available serial port, proceed with the following steps.

For Windows XP users: (Vista users - Skip to Vista)

1: Left click on the Window's Start Button at the bottom-left of the screen
2: Use the RIGHT mouse button to click on "My Computer"
If your system does not have the "My Computer" icon, skip to Control Panel method

3: In the Popup menu, Left click on "Properties"

 

If your system has the "My Computer" icon, skip to step 4

 

Alternative Control Panel Method
If your system does not display “My Computer” item in the Start Menu list, you may also gain access to the “System Properties” window by double clicking the “System” icon from the control panel.

1: Left click on the Window's Start Button at the bottom-left of the screen
2: Left click on “Control Panel”

3: In the “Control Panel” window, double left click on the “System” icon. This will open the "System Properties" window.

 

 

For either method used, the “System Properties” window should now be opened.

In the "System Properties" window:  

4: Near the top of the "System Properties" window, left click on the "Hardware Tab"
5: Double left click on the “Device Manager” button.

 

This will open the “Device Manager” Window.

XP users should Skip to Device Manager Section

For Windows Vista users:

1: Left click on the Window's Start Button at the bottom-left of the screen
2: Use the RIGHT mouse button to click on "Computer"
3: In the Popup menu, Left click on "Properties"

 

3: In the “System” window, left click on the “Device Manager” link.

 

This will open the "System Properties" window.

For XP and Vista:

The "System Properties" window is now open. This is a structured list of your system hardware.
This list includes all ports available to your system’s hardware or software.

If there are any available ports, one of the primary list items will be titled “Ports” and may contain more descriptive text after similar to “Ports (COM & LPT).”

Left click on the “+” icon to the left of the item title will expand the list to reveal all available ports. The port item in the list contains a port description followed by a port number.

Your USB adaptor port should be obvious from the description, it should include the manufacturer’s name and/or some form of the words USB adaptor.

The example above list a USB to Serial adaptor made by Keyspan which has been assign with COM5. This system also shows a built in port, COM1.