I'm working on some new instrument interconnections and found some interesting reference material to pass along, FYI:

http://www.cruisersforum.com/forums/f13/nmea-0183-and-rs-422-vs-rs-232-a-12967.html#post858371

http://www.actisense.com/Downloads/TechTalk/NMEA%200183/The%20NMEA%200183%20Information%20Sheet.pdf

I also bought an inexpensive Converter to bring NMEA data to the CP which requires RS422. http://www.amazon.com/RS232-To-RS422-Converter-Adapter/dp/B003MMS92O/ref=sr_1_1?ie=UTF8&qid=1326548615&sr=8-1 will let you know how it works when the weather warms up. BTW my project is to deliver heading info from the Raymarine heading sensor which is Seatalk, through a seatalk conversion to RS232 NMEA0183, to RS422 to the Lowrance HDS7 Which requires a heading sensor to enable radar overlay on charts.