This is the reply I received from Garmin when I presented them with the same problem.
Thank you for contacting GARMIN International.
I would be happy to help you with this. If you do not have a serial connection on your computer, you will need to get either a USB to serial converter cable or a PCMCIA card with a serial connection option. The application of a USB to serial converter is a very delicate issue. The USB to Serial converter that Garmin is currently offering has been tested on
multiple brands of computers as well as on multiple operating systems. The
capability of any USB to serial converter from any manufacturer to work on any given machine has about an 80% success rate. We do not recommend the Garmin cable over any other brand as the success rate is the same.
My supervisor has personally done extensive testing on our USB to Serial converter, as well as converters manufactured by KeySpan and Belkin. The success rate is approx 80% across the board. The deciding factor seems to be the configuration of the specific machine. He can take 5 identical computers, same manufacturer, same operating system, utilized for the same purposes, so the same software has been installed/removed. These are as close to five identical machines as he can get. Then since each computer has had a slightly different life, they have different configurations when it comes to the Windows Operating systems. He can then take the three different converters from the three different manufacturer's. In testing varying levels of compatibility then occurs using each converter on each individual machine.
The serial to USB converter is a delicate conversion to perform due to the creation of the Virtual Com Port. The way that Windows then handles this virtual com port including any other hardware conflicts is up to Windows. Our customer's experience has paralleled our experience with USB to Serial interfaces. Factors in the users PC seem to be the limiting factor for
compatibility with one or any of the USB to serial converters. For this
reason, we always recommend contacting your pc manufacturer to find which one they might recommend for use with their particular systems.
If you have attempted one type of USB to serial converter, and it is not working for your application. I would recommend returning it to the place of purchase for a refund. Then I would recommend exploring the USB to Serial converters produced by other vendors to see if one by another manufacturer will be compatible with your application.
The PCMCIA option has a better success rate, however it is not a 100% solution either. The only 100% solution is to have a direct serial connection.
At this point in time Garmin is the only GPS manufacturer that I am aware of to offer a USB to serial conversion. In the GPS industry serial communication with the units is still the standard as a large portion of our customer base depend on a NMEA protocol to interface with other devices. NMEA data will not stream through a direct USB interface.
With Best Regards,
Senior Product Support Specialist
[This message has been edited by Jimmi640 (edited 20 July 2004).]