Tip: Garmin 296 Setup for COM ports

[hevansrv7a]

Background: I have the GRT EFIS and the TT autopilot. I wanted to send GPS data to the TT through the EFIS for full functionality. I also wanted to have a direct path from GPS to TT in case the EFIS quit in the clag. The power-data cable from Garmin has two COM outputs, #1 and #2. I have a selector switch next to the TT for which source to use.

I used both COM wires. Then I tried to configure them (see pp 115 in the manual). I discovered you cannot configure them both the same. Garmin tech support confirmed this today. The work around is to use Aviation In/NMEA out on one and NMEA in/NMEA out on the other. Watch out for the Baud rates. Notwithstanding what it says in the book, you cannot set them. Aviation in/NMEA out will set itself to 9600 and NMEA in/NMEA out will set itself to 4800.

Also, if you haven't already done the wiring, just use one and split the wire. Garmin says you can support as many as three devices from a single COM port.

Anyone know if this problem exists in the 396 and/or 496?

[Brantel]

I think you can connect both devices to the same port since all they are doing is "listening" to the serial stream.

As long as you do not connect so many devices that the input impedance becomes so low that you drag down the output of the 296 it should work fine.

Sorry I just read your second to last sentence where Garmin told you the same thing I just mentioned above.

[Pirkka]

Originally Posted by Brantel

As long as you do not connect so many devices that the input impedance becomes so low that you drag down the output of the 296 it should work fine.

In that case some sort of buffer or repeater could be considered. In ideal situation there is no problem, but if design of devices is poor you may encounter problems easily. So what out what to connect there and verify if necessary. Doing repeater of your own for such a slow speeds shouldn't be too hard either.