Check the version of NMEA that the Garmin is using. You should be able to chose between 2.0 and 1.5. If you look at the "Words" that the Garmin uses, they have better communications with the older level (1.5) than the newer level (2.0) You also need to look at the "Words" that the ICOM 502 can read.
By switching the NMEA on my Garmin to 1.5, I was able to get my GPS 128 to talk to my NEXUS network and my ICOM 502.
05-05-2005 12:13 PM
Icom Garmon NEMA communication
I have having trouble with my NEMA communication between my Garmin 172C GPS/Plotter and ICOM M502A VHF. I have the GPS set to communicate on both port 1 & 2 at NEMA in/out. However, when I turn on the position feature on my VHF, I have the message "NO POS DATA". The two units are connected via a red rca plug. Any help would be greatly appreciated.