FYI:
http://www.gpsfaqs.org/faqs/garmin/xseries/g60csx/cabling.html

There are three ports on the back of the unit. The USB-A to USB-B, the four pin Garmin and a very small one for an additional antenna. Pictures...
http://www.letsgomobile.org/en/review/0058/garmin-gpsmap-60csx/page2/
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