I have a RayMarine C80 as my primary chartplotted which interfaces to a RayMarine SmartPilot S3 via SeaTalk. I used to have a Northstar 6100i as a backup chartplotter, which interfaced to the SmartPilot via NMEA 0183. The NorthStar died and I replaced it with a Garmin 740s.
The Garmin receives NMEA data from the SmartPilot on both NMEA ports without issue, but didn't control the autopilot. To see what sentences the Garmin was transmitting, I connected the xmit to the receive line (on the Garmin) and I see 0 sentences being transmitted. I tried it on both port and cross connecting the ports, but still nothing. It's like the Garmin isn't transmitting anything. The ports are configured to be NMEA Standard. I'm completely at a loss as to why I don't see any data being transmitted. Any ideas?
Of course we're on the Pacific side of Mexico trying to get ready to depart for El Salvador on Monday and Garmin tech support is closed until then.
-- Geoff
Garmin usually has a xmit speed setting. Did you try changing it?