Yes the sentences are configurable, I suspect that may be the issue, I need to figure out what "list" I need and minimize what is being transmitted. It looks like CE is might be sending the whole library. I do have the 300X and yes the E-120 is going to the NMEA2 port (eventually)
The two common NMEA 0183 Autopilot sentences are APA and APB.
APA Autopilot Sentence "A"
$--APA,A,A,x.xx,L,N,A,A,xxx,M,c---c*hh
1) Status V = LORAN-C Blink or SNR warning A = general warning flag or other navigation systems when a reliable fix is not available
2) Status V = Loran-C Cycle Lock warning flag A = OK or not used
3) Cross Track Error Magnitude
4) Direction to steer, L or R
5) Cross Track Units (Nautic miles or kilometres)
6) Status A = Arrival Circle Entered
7) Status A = Perpendicular passed at waypoint
8) Bearing origin to destination
9) M = Magnetic, T = True
10) Destination Waypoint ID
11) checksum
APB Autopilot Sentence "B"
$--APB,A,A,x.x,a,N,A,A,x.x,a,c--c,x.x,a,x.x,a*hh
1) Status V = LORAN-C Blink or SNR warning A = general warning flag or other navigation systems when a reliable fix is not available
2) Status V = Loran-C Cycle Lock warning flag A = OK or not used
3) Cross Track Error Magnitude
4) Direction to steer, L or R
5) Cross Track Units, N = Nautical Miles
6) Status A = Arrival Circle Entered
7) Status A = Perpendicular passed at waypoint
8) Bearing origin to destination
9) M = Magnetic, T = True
10) Destination Waypoint ID
11) Bearing, present position to Destination
12) M = Magnetic, T = True
13) Heading to steer to destination waypoint
14) M = Magnetic, T = True
15) Checksum
Note: Some autopilots, Robertson in particular, misinterpret "bearing from origin to destination" as "bearing from present position to destination". This is likely due to the difference between the APB sentence and the APA sentence. for the APA sentence this would be the correct thing to do for the data in the same field. APA only differs from APB in this one field and APA leaves off the last two fields where this distinction is clearly spelled out. This will result in poor performance if the boat is sufficiently off-course that the two bearings are different.
Simplifying the data string out should definitely help in this situation, especially since it is a dedicated autopilot port.
Best of luck!