Tom, you'd have to read thru all my posts to find those answers, lol, but to sum it up, the p70R lists all it's components and the Garmin GPSMAP 541, and nothing else. Not even an unknown! And when the GPSMAP 541 is shut off and/or disconnected, the Raymarine p70r has no position data or any thing else other than what it's components can provide. I just got off the phone with Garmin. First I spoke to a tech on the GPSMAP side. She indicated that if the 541 was being read, then so should be the 840. I understood from her that the protocol was no different. However, she said using a 5 way connector in the NMEA 2000 system would be a red flag. (Seatalkng does use 5 way connectors, along with T's). Since I plugged the 840 in to the wire I had the 541 on, still with no resolve, I have a hard time buying into a backbone issue. But I guess anything is possible. I then transferred to Garmin's Autopilot techs to talk to them, and this tech indicated that the 840 might have a different protocol that the 541. In speaking to either of them, it sounds like the only way to know anything for sure would be to hook a computer tester up to the NMEA 2000 system. ($$$ and no shops capable of doing that in my neighbrohood....) Thinking more about switching out the Raymarine system to the slightly more pricey Garmin GHP10 system, I now wonder if I could end up having problems with that and the 840 communicating. When you go to Garmins website and look for compatible equipment on the GHP 10, it does not show the 840, and the 840 shows their newest "Reactor" autopilot series. However the tech said the 840 and GHP10 were compatible. I already have the Raymarine stuff installed, and not even sure Hodges Marine would allow me a full refund to exchange for the more expensive Garmin. (I have a request into them to see.) From the start I thought the Garmin system had some better specs (mostly with the larger pump, shadow drive and the fact I already have Garmin electronics) however it was about $1000 more expensive. The Raymarine looked like a nice unit for the price, and many here had good experience with it. But with running into compatibility issues with the main Garmin MFD I wanted to use it with, and the software update issues, I'm thinking the extra cost of the Garmin would probably have alleviated all this additional frustration. (I note however, the Garmin A/P tech strongly suggested having their unit professionally installed. I'm sure that would add several hundred more dollars to the cost, and I think if one is mechanically capable, shouldn't have to pay the additional labor charges....) The only other suggestion I have been offered by Garmin with regards to their equipment communicating with Raymarine, is to possible change up the back bone. Ie, use T's only, rather than the 5 way connector. I just have a hard time thinking that would change anything, with everything else I have tried, and since the 541 is communicating with the Raymarine. I'm beginning to believe that the 840 does in fact use a different protocol than the 541, that the P70R does not recognize! Colby