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Internal GPS Baud Rate

PostPosted: Mon Mar 07, 2016 1:53 pm
by N651RV
I have just added a GTN 650 to my system and there seems to be a Baud rate conflict between the GRT Internal GPS and the GTN 650 GPS when I try to switch between the 2 to drive the Tru-Trak autopilot. Current set up is as follows:
Sport SX c/w Synthetic vision and internal GPS and ARINC 429 Module and powered USB hub for Bluetooth using the GRT app.
GTN 650
Vizion 385 Autopilot.
I have a switch allowing the feed to the autopilot to be selectable between the GRT internal GPS and the GTN. The problem is the Baud rates, the autopilot needs to be set at 9600 to receive the GTN 650 feed but needs to be set at 4800 to receive the GRT signal. I have tried the autopilot at both Baud rates and it works with the respective feed.
Is there any way I can set the GRT to 9600 and feed the autopilot? I have tried setting serial port 3 to 9600 but the autopilot did not recognize the signal.
I don't want to change the autopilot setting every time I change GPS source.


Re: Internal GPS Baud Rate

PostPosted: Thu Mar 10, 2016 5:15 am
by jnewsum1
I think you should be using pin 34, Tx1 A/P Serial Output to drive the Vizion 385 from the GRT SX EFIS. The SX Installation Manual defines this RS232 serial output for transmitting the internal GPS data plus heading, altitude, etc. to an external autopilot like the Vizion 385.

On my Sport HS EFIS, I have pin 34 connected to a Vizion 385 via a switch that allows selecting either the Sport EFIS or a Garmin GNS430 RS-232 serial ouput to drive the Vizion AP. It works properly with either device selected. All three devices (Sport, GNS430 and the TruTrak) are configured for 9600 baud Tx output

For the internal GPS serial output, the Sport Installation manual indicates that serial port 3 (pin 32) should be configured for 9600 baud (page 4-29 in Revision E) for connecting to external devices. Its possible that this output can be used to drive the Vizion, but for sure pin 34 will work.

One thing I learned the hard way in my installation, is that the Sport EFIS only supports one ARINC 429 GPS input and the ARINC 429 GPS input must be GPS1. I don't think is defined in the Sport Documentation, at least I couldn't find it. GRT tech support did confirm this limitation.

Re: Internal GPS Baud Rate

PostPosted: Thu Mar 10, 2016 8:01 am
by GRT_Jeff
The internal GPS data on serial port 3 on the Sport is position data only and can't be changed. It does not contain any autopilot data. You need to set up one of the other ports as an Autopilot output if you want to drive the autopilot with a serial connection. Are you also using ARINC-429 to drive the Vizion? In that case, you don't need to switch the serial connection, only the ARINC-429 connection. We normally leave the TruTrak's serial input connected to the 650 when ARINC-429 is also connected.

Re: Internal GPS Baud Rate

PostPosted: Thu Mar 10, 2016 9:13 pm
by N651RV
Thanks Jeff and Jnewsom1,
I realize my mistake now, During the install of the GTN650 I rewired the autopilot feed from pin 34 to pin 36 (Serial 3 TX) without thinking. I had my mind set on the EFIS having 2 Autopilot outputs External from pin 34 and internal from pin 36. As soon as I read your post I realized what I had done. Looking back to my original wiring diagram from 2008 (sport WS) I had pin 34 as internal GPS output, somehow I overlooked this during the install of the GTN.

Problem solved,

Thanks again