RFD900+ (RDF868+), RFD TXMOD V2 - wiring, PPM, RTS/CTS pins, Mavlink questions


I’ve just wired up the RFD 868+ and TXMOD V2 with Pixhawk 2.1, all is working well so far but I got couple questions regarding this system.

  1. What are all those telemetry pins, why do I need 4 of them ? I mean there is: CTS (TX), RTS (RX), TX and RX + RCin on servo rail. Can somebody explain what is going on on all those pins and why do I need 4 ? Normally, I’d expect only transmitting and receiving pin for telemetry + RCin.

  2. Is there any other way to use PPM for RC control, than plugging in pin 15 to RCin port on servo rail ? Isn’t it possible to send RC control link PPM via telemetry port to control the aircraft straight from the Taranis ?

  3. Is there any other way for displaying telemetry data on Taranis X9D+ apart from Yaapu script ? It was possible with crossfire, but Taranis wont discover any sensors with RFD900.


Hi @BennetEown,

  1. These pins are the serial (UART) data lines that the RFD would use to pass telemetry messages between itself and your flight controller. The RTS (ready to send) and CTS (clear to send) lines (from memory) are used by the serial devices at higher data rates to indicate if they’re ready to ‘talk’.

As a side note to that, if you want to pass telemetry, you would need a cable to go from PixHawk Telem1 to the RFD (assuming, of course, that you don’t already have one).

  1. I think there’s a way to pass PPM in the MAVLINK traffic, but I don’t know if the TXMod would be able to inject it’s channel state into the MAVLINK traffic.

  2. I don’t know - I didn’t think that the YAAPU script would work if you don’t have a FrSky receiver on the aircraft. AFAIK, The Taranis ‘discover sensors’ option looks for FrSky S.Port devices.

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Yaapu will work with the TXModV2. It has some quirks and you will get false warnings but it will give you all the normal Yaapu telemetry data.