RFD900x SBUS / PPM support added

Hi Everyone,

Thought to give an update on the RFD900x series modems, that we have added SBUS support from version 3.09 onwards. It also supports translation to/from PPM on both the ground and in the air side modem, so should make configuration options quite flexible!

Keen to hear feedback on the experiences with how it works for you.

Seppo @RFDesign


Hello Seppo,
Could you send me some instruction please?

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Hi Seppo @RFDesign
This update v3.09 is in beta.
Is it safe to use the beta version for a ready to fly vehicle (OR just for beta testing purpose)

For the ground based modems, either RCIN or SBUSIN should be checked.
For air based modems wither RCOUT or SBUSOUT should be checked.
They can be mixed between RC(ppm), or SBUS in the air and ground, the modem will translate both ways.

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RFD900x-3.09 has been released for a while we have not had any issues to date, PPM is very stable, has been in use for almost a year, but, it would be good to have feedback for SBUS, that has been in use for 2-3 months.

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I have tested this in my RTF Hexacopter without any issues.
Have done number of flights until now.


Hi Matt,

If there are any conflicting ppm/sbus settings, that could be precluding the parameters from being set.
Would you be able to do a factory reset, (Restore defaults button), or AT&F, AT&W, ATZ on the modems and try to re-set the PPM/SBUS settings?

If there are still issues, would you be able to downgrade the firmware to an older version, V2.53-4 or so and re-upgrade to 3.09. This will also force a parameter table reset internally.


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Hi Seppo,

I too am having the same experience as Matt; I tried both a firmware downgrade to V2.53 and restoring defaults but am still unable to get SBUS passthrough working.

I am sending 16 channel SBUS from an FrSky X8R receiver to the RFD900x.

For clarity, should I be using Pin #15 or Pin #12 for the SBUS in and out?


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Hi @Matt_C, those directions work perfectly, thanks.

@Seppo, would it be possible to add a feature for SBUS failsafe options? At the moment it seems like the default is to output ~820us on all 16 SBUS channels in the event of loss of radio link, but for our application it would be much better to simply not send any pulses at all. Would it be possible to add that option to a future release?


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@Matt_C Thank you for detailed help. SBUS is working now.

Currently I have 3 problems:

  1. Configuration utility is not working
  2. Using AT commands I can’t configure R0 (0 TARGET_RSSI) and R1 (HYSTERESIS_RSSI). It doesn’t allow to enter big numbers like 150 or 255. Default values are very small. Is meaning of values the same?
  3. I can’t set encryption key using AT&E=5AEEF103125C0AA233678909160111CA


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I can’t figure out how to set Sbus Failsafe.
Anyone please help!!

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HI @Seppo

To enable SBUS PASSTHROUGH can pin 15 of RFD be connected to SBUS of X8R directly ?
I mean no need to add logic shifter Or pull up or anything else, just a straightforward direct connexion ?


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Hi Matt,
Thanks for you answer, it’s clear !

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@Matt_C , is it also the same with L9R ?

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Did you figure out anything on this?

I’m also having issues with SBUS fail safes…

Gcs failsafe works on loss if heartbeat for sbus but if I connect without gcs and use it in rc mode then failsafe does not work. If link is lost then plane will stay in last flight mode a d also get lost.

This seems to be an old thread, but I am wondering if anyone has a RFD900x module and has an issue with setting the remote unit’s encryption key while in certain settings. I am noticing that if you configure a unit with SBUS Input : ON and SBUS Output: OFF (0), then it is unable to write the remote unit’s encryption key using RT&E=, while AT&E= command continues working. It is also able to configure other parameters on the remote unit, just not the encryption key. The RFD desktop application further complicates the problem by continuing and saving the parameters, so in the end you get two units that have become unpaired with different encryption keys. Is this expected behavior?

I would email RFDesign about that: support@rfdesign.com.au

I was able to get a reply from RFDesign. It is currently a bug that when SBUS data is being inputted into the RFD module (w SBUSIN enabled), sending RT&E= while in Encrypted mode does not work most of the time. They will fix this bug in a future FW release. A workaround for now is to disable encryption and then set a new encryption key while setting the modems to Encrypted mode.