No telemetry out of Uart on Matek F405-SE AP4.1.7

Hi, I’m trying to setup ArduPlane 4.1.7 on Matek F405-SE with Taranis X9DP and R-XSR receiver. Everything is working, including GPS, RC, but I can’t get telemetry working.
I’m using the Inverted S.Port pad on the R-XSR that should mean I don’t need inversion hardware.
I’m connecting to Uart TX1 on the F405-SE.
I’ve set SERIAL1_PROTCOL = 10, SERIAL1_OPTIONS = 4 and 7 (tried them both). BAUD = 57.

Using an oscilloscope I can see the UART TX1 line toggling for half the time, but this is coming from the X-XSR, not from the F405-SE. When I probe the TX1 line without R-XSR connected, there is constant 3.3V but no toggling.
I tried on TX4 as well, 3.3V without toggling.
I can see TX3 (GPS) toggling.

Is there something else I need to do to get the UARTs to output Telemetry?


After a lot of experimenting I’ve gotten it to work.
When I flashed the R-XSR receiver with the latest ACCESS FW, it seems its S.Port pin changed to using F.Port. The Ardupilot serial protocol for S.Port is 10, but for F.Port I needed to use Serial1_Protocol = 23.

Both S.Port and F.Port are half-duplex (so I’ve read online) so I do need to configure Serial1_Options = 4. The advantage of this is that I don’t need to use a separate SBUS signal to carry the RC, as F.Port does both RC and telemetry over the one wire.

This now correctly sends telemetry back to my Taranix X9D+ which is evident in the Yaapu script correctly showing all the values, however in OpenTx when I search for new sensors it only finds GPS, and none of the others. I suspect this is a problem with OpenTx.