Hello Paul of MapWindow fame ;)
FYI: A refactored and more up to date version of GPS .NET is being merged with DotSpatial as DotSpatial.Positioning. The merged version isn't working right now but if you look in the repo folder DotSpatial\DotSpatial.Positioning\DotSpatial.Positioning.Compact
you will find the most up to date version refactored into the DotSpatial.Positioning namespace - apart from the refactor it still works pretty much the same.
In answer to your question: Garmin GPS by default generally use their own proprietry phase-interlock protocol. This protocol has been changed by Garmin so many times that Jon Pearson (GeoFrameworks) paused development
of support for the Garmin protocol some time ago. I have had some success in connecting to some early Garmin models (e.g. GPS Pilot, GPS Map series) but more recent models seem to have changed the comms protocol yet again :(
If you just want to use the Garmin GPS as a "normal" NMEA GPS you can do so with most Garmin models by going to the Setup screen and changing the Serial Data Format option to NMEA In/NMEA Out (see your
specific GPS manual for more detail). Operating in this mode your serial (RS232) connected Garmin should detect just fine regardless of baud rates and other config options.
Garmin USB is a different matter - the Garmin USB driver is proprietary for use with Garmin software see this article for a rant on the topic:
http://www.oreillynet.com/xml/blog/2004/10/garmin_gps_goes_more_proprieta.html they definitely haven’t been making a lot of friends with their current stance on interfacing and 3rd party software support.
If you really want to use your Garmin GPS via USB you can consider products like
http://gpsgate.com/products/gpsgate_client to interpret the proprietary data and supply NMEA data to your applications via a virtual comm port.
With the cost of excellent quality USB interfaced/powered GPS units plummeting the question is: Do you really want to use your Garmin at all? If your interfacing to a PC then you’re possibly running some kind
of software that makes the Garmin map display etc. redundant though this is a bit of an assumption….