There are four pins on the back of the Garmin. Clock, data, power, and ground.
The ground, clock, and data go to the RS-232 plug. You don't HAVE to have
external power, but since you are making up the cable anyway, why not just bring
out the power and an extra ground wire? That way you can run it from a Rat
Shack 12v power supply if you want.

Can you use the internal batteries? You bet. However, getting in the middle of
an upload and having the batteries go flat isn't going to please you.

Jim




"Roger Long" om
shared these priceless pearls of wisdom:

-Jim,
-
-Thanks for your kind offer. I assumed when I posted that the PC interface
-would include a little dongle with buffers, converters, and whatnot. I didn
-'t realize it's just a cable. I've homebrewed innumerable computer cables
-so I should be able to manage this.
-
-Thanks for the pfranc lead.
-
-I'm a bit confused though about their instructions and the business about
-the computer port not being able to power the Garmin. For just a database
-upgrade, can I let the batteries run the GPS and just ignore the power
-issue? Should I just make up the cable with just the data wires?
-
-I'll probably figure this out when I study the pfranc site some more but any
-clarification would be appreciated.

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com