So today I was building a new quad, with a brand new R-XSR receiver.
I dry-fitted the build to make sure everything was working before putting them together (connected all the components, powered them up and making sure they are all working correctly, including SBUS)

However, after assembly, SBUS just stopped working! The receiver is powered on and bound, SmartPort is still working fine, but I wasn't getting any signal in the Receiver Tab...

I tried everything I could think of:
- Redo the soldering
- making sure SBUS is selected on the FC (on the BFF4 board, you need to select PPM or SBUS by bridging the pads)
- make sure "SBUS inversion" is on in BF CLI
- I even flash BF firmware again on the board to avoid any bad settings...

Still no luck.
Then I tried choosing PPM in Betaflight, and it bloody worked! 

How the hell is my R-XSR giving out PPM signal?

Then I turned to the R-XSR manual, and found this:



Apparently if you hold down the F/S button for too long, it will switch to CPPM mode! I think I must have done that when I was setting up failsafe and set the RXSR in PPM mode!
Long press the F/S button for 4 seconds again and we are back in SBUS mode, hooray!

It took me a long time to fix this problem, I thought I would share the story and it might save somebody the headache one day 

Thank you Oscar!!! That will save a lot of pain in the future as the R-XSR starts to take over.

Oscar, on two of my new builds the R-XSR are not working. I switched and XSR works though, I posted it in a thread. Not sure what to do. Lumineer F4 AIO FC.
First I saw what you posted it and I had the same problem, I switched to Sbus and it still doesnt work. I unplug R-XSR and plug in XSR and it works fine. I do not know what to do?

(08-Dec-2017, 01:46 AM)Mick1000 Wrote: Oscar, on two of my new builds the R-XSR are not working. I switched and XSR works though, I posted it in a thread. Not sure what to do. Lumineer F4 AIO FC.
First I saw what you posted it and I had the same problem, I switched to Sbus and it still doesnt work. I unplug R-XSR and plug in XSR and it works fine. I do not know what to do?

so by the sound of it your FC is configured correctly, and the issue is related to the R-XSR you have.
Is it binding? what colour LED do you get on the RX?

You should have a green solid LED.

Thanks Oscar for your page and the advice you share there and on here, I've been reading through it for a few weeks now and it's really helped me out moving from 450 quads to more modern Mini Quads!

Unfortunately I've run into a few problems along the way, the latest one I've described below:

I don't seem to be able to get any receiver signal through to the board when using SBUS - with the receiver in SBUS mode as you described above and wired to the SBUS pin (which I believe un-inverts the signal) I get no response within Betaflight. What is really weird is that if I switch the reciever and quad over to PPM (using the same pin and UART) it works fine? I could leave it on PPM as it does appear to work but I'd love to have it working the way it was intended on SBUS!

I haven't yet modified the reciever to output un-inverted SBUS, I was hoping to avoid it especially since the Matek supposedly switches it itself...

I do have functional Smart Port telemetry after following your guide on SoftSerial, so the receiver is mostly working....

I've set everything as described on the Matek product page (SBUS on config page, UART 2 with Serial RX enabled)

Anything I should try out? Thanks in advance!

Controller: Matek F405-AIO
Reciever: FrSky R-XSR

Are you definitely using the "SBUS" pad on the board? (not RX2, but the pad next to it)
also try setting sbus_inversion = OFF or ON (should be off)

Sbus_inversion is a F3 command, does not work on F4 board.

Can you show a photo of your wiring and configuration tabs.

(16-Dec-2017, 03:24 PM)Oscar Wrote: Are you definitely using the "SBUS" pad on the board? (not RX2, but the pad next to it)
also try setting sbus_inversion = OFF or ON (should be off)

Hi Oscar,
Thanks for the response

I've just confirmed that I'm using the SBUS pad.

SBUS_inversion WAS on, however that was probably me fiddling around trying different combinations. I've now switched it back to OFF, though I had the understanding it was ignored on F4 boards anyway?

(16-Dec-2017, 05:04 PM)voodoo614 Wrote: Sbus_inversion is a F3 command, does not work on F4 board.

Can you show a photo of your wiring and configuration tabs.

Hiya since there's a few photos/screenshots I uploaded them in an album:

https://imgur.com/a/EvBoA

In the photos I've switched the receiver to SBUS mode, and updated the config to SBUS. Pin is the same SBUS pin I was also using for PPM (which was working )

Thanks for checking this out!

everything looks correct so far..
is the white wire *SBUS_IN" from R-XSR connected to something? remove that wire from the connector if it's not used.

I am out of idea here, maybe try to flash the latest RX firmware see if you have any luck.
If nothing works then it's probably an RX issue? unless you have a different SBUS receiver and it doesn't work on this FC either.

Unfortunately I have already flashed the latest FCC firmware to this one

The white wire at the moment is just floating, didn't want to chop it until it was all working

I've got a spare XM+ here from a hobbyking warranty replacement, so I'll give that a go next. Last one I had died within minutes of opening the package so I'm not that hopeful...

Thanks for your help!

Sounds like the inversion hardware in your FC might be defective. I would get the R-XSR non-inverted SBUS and see if it works.

Or you can screw SBUS altogether and use the new F. PORT protocol.

Alright I may give that a go, thanks for the advice!

I'd like to avoid modifying the receiver if I can, just incase it is defective I'd be able to take it back to the local store I bought it from if it was un-modified

Hmm I haven't heard much about F.Port, I'll give it a bit of a google and see what comes up

Okay.

I was reading about some issues with non-standard boards doing serial port parity bit inversion (down the rabbit hole, reading Betaflight issues page) on some SPRacingF3 boards for the micro quads and had a bit of a think. There seemed to be reports that with that board SBUS wasn't working on any verison of Betaflight past 3.1.7, and the culprit appeared to be some changes made to SBUS compatibility - namely to increase compliance with the spec I believe:

https://github.com/betaflight/betaflight/issues/4710

That made me think about my board - which shipped with 3.1.7, which I immediately flashed to the latest release of Betaflight when I purchased it, 3.2.2 (I also tried 3.2.3 BTW)

I've just downgraded the board to 3.1.7 - and it WORKS! I now have SBUS working perfectly with the R-XSR on the Matek F405-AIO.

So this makes me think that the Matek F405-AIO (or R-XSR?) might be suffering from the same issue of SBUS parity bit inversion... though I wouldn't have a clue who to report this to!

At least I'm up and running, however moving to such an old Betaflight version I believe I'm sacrificing some features like Turtle mode and others.

Should I stay on 3.1.7 for now and use SBUS, or upgrade to 3.2.3 and just use PPM? I'm new to racing quads, all my previous quads/tricopters used KK2s! There's so many features to play around with it's hard to tell whats actually important and what's merely clever

Thanks everyone!

But I have the Matek AIO and R-XSR working perfectly on BF 3.2.3 though (latest firmware)
if you definitely cannot get sbus to work in latest firmware, it's best to use latest firmware with ppm. The slight increase in latency isn't going to be noticeable IMO.