Tablet PCs, like many new notebooks (and a few desktops), are "legacy-free" devices; they have USB ports, but they don't have conventional serial or parallel ports. Eliminating serial ports is necessary for the support of "surprise undock" and full-function standby and resume; however, it causes a problem when you need to connect a legacy serial device, such as an older PDA synchronization cable or Global Positioning System (GPS) receiver.
One workaround is to purchase USB-to-serial adapter cables, which are available from a variety of vendors. I purchased a Prolific PDA USB Adapter cable at my local CompUSA for about $29. The cable has a USB connector on one end and a female DB-9 serial connector on the other. The adapter cable came with a CD-ROM that contained a serial port driver.
When I installed the Prolific driver on Motion Computing's M1200 Tablet PC, the driver defaulted to the COM5 port, which wasn't compatible with the software I wanted to use with my GPS. And the adapter's documentation wasn't clear about how to reconfigure the port. After some Web research, I discovered the following procedure.
Go to the Control Panel System applet and open Device Manager. On the Hardware tab, select Ports and right-click Prolific USB-to-Serial Comm Port (COM5). Select Properties from the resulting pop-up menu, go to the Port Settings tab, and click Advanced. At the bottom of the "Advanced Settings for COM5" dialog box is a list selector, with which you can select the COM port number to use. I switched to COM2, and everything is working fine. The procedure might vary for other vendors' adapter cables but will probably be similar.