GRT Avionics

I have Sport Ex, Aera 796 and Garmin GTR 200 ….
Both Sport Ex and Aera can output standby frequency selection and am planning to connect both Sport Ex serial out and Aera serial out to the same GTR 200 serial in and use both devices to select standby frequency on the radio … do you foresee any issues using this sort of multiplexing ?

Thanks

Generally speaking connecting two ‘outs’ to one ‘in’ is asking for trouble. What happens if both ‘outs’ send signals to the ‘in’ at the same time?

It's worse than that. Even when one is not sending it will still interfere and fight with the other trying to send data. Normal RS232 is always driving the output trying to force the wire to a specific voltage and that includes when idle. The only way to connect two outputs is to have a switch to select one (or build something complicated if you're into electronics).

So I am curious how does the autopilot work since it is multiplexing serial ports to/from the EFIS … does it use some other protocols than RS232 ?

I was planning to control the problem of sending commands at the same time by simply using either Aera or Efis one at a time , depending on what was more convenient but I was not sure if there would be an issue in terms of actual physical connection ( voltage ) … but if it can’t be done , then it can’t be done

Thanks

You may take the OUTPUT of the GRT **servos** and send that to multiple places (e.g. EFIS's).

The INPUT to those servos needs to come from just ***ONE*** EFIS.

I have a switch that selects which EFIS **controls** the autopilot servos. All of my EFIS's get to listen.

Now, there have even been cases where a non-controlling/just listening EFIS has gotten confused. I think this might be a random/intermittent bug based on info that might be shared over the InterDisplayLink. (Jeff correct me if I am wrong on that.)

When you have two servos (roll and pitch) their outputs are connected together. The servos have a simple serial transmitter that's compatible with most modern RS232 receivers at 9600 baud. I think the main thing is the negative voltage is weaker. It allows one of them to drive the wire while the other is idle. The EFIS controls when they talk so they don't try to talk at the same time.