COM ports for GPS Mapping

A COM port is a computer serial port that’s used to connect a mouse, modem, or other device, like a GPS receiver. (COM stands for communication, and the ports are called serial ports because they receive data serially, one character at a time.) COM ports typically have a small oval, D-shaped connector (with nine pins) and are located on the back of your computer. (If you have other devices plugged into your serial ports, you’ll need to unplug them so your GPS receiver cable has a port to plug in to. You can plug the other devices back in when you’re through transferring data with your GPS receiver.) Your PC might have one or two physical serial ports that you can plug devices into, but Windows allows you to assign a COM port number to each device. These numbers usually range from 1 to 4 but might go as high as 256 if a USB adapter is used, (which I talk about in the upcoming section, “USB ports”). In most cases, you won’t need to use Windows to reassign any of the port numbers. Just know that you have numbered COM ports and that you need to assign one to your GPS receiver, which I talk about next. To get more detailed information about COM ports and Windows, including how to change settings with Windows Device Manager, head to the Microsoft support Web site at http://support.microsoft.com and search the Knowledge Base for com port. Or pick up a copy of PCs For Dummies, 9th Edition (Wiley) by Dan Gookin, which has an excellent chapter that clearly explains everything you need to know about the subject. The program you’re using to interface with the GPS receiver is where you need to specify which COM port number the receiver is connected to. Programs typically use a drop-down list box that shows all the COM ports; just select one from there. (Some programs have an autoselect feature that tries to establish communications on all available COM ports until the port with the GPS receiver is found.)