The Missing UART6 in the BetaFPV F4 AIO 12A/20A/35A FC

by Oscar
Published: Last Updated on

If you are using the BetaFPV F4 AIO 12A/20A/35A FC, and can’t find UART6 (TX6, RX6) in the ports tab, here is why. I had a tough time figuring this out, thought I should share to save people’s time.

Product Page

Missing UART 6?

Well, there is no UART6 on this board, simply never existed.

The labelled TX6 and RX6 in the pinout diagram are actually Softserial 1! I think this might have “tricked” some people into getting this FC and thought it had 3 hardware serial ports, but in fact it only has 2.

Further Reading: What’s a UART?

That’s why you don’t see UART6 in the ports tab in Betaflight, but there is Softserial 1, which they already set up for you. You need to connect your device to TX6 and RX6 to use Softserial 1.

This is annoying, but not the end of the world. You can still use softserial for a lot of things that aren’t “timing critical”, basically almost everything apart from RC links.

To put it simply, you can use Softserial for SmartAudio, SmartPort Telemetry, GPS, Camera Control, DJI UART, and so on, but you SHOULD NOT use it for SBUS, Crossfire etc.

Further Reading: What’s Softserial?

Wrong Softserial Config

The “fun” doesn’t stop there, they even configured Softserial wrong, so it’s not going to work properly :D

If you type Resource in CLI, you might find the pin B03 is assigned to both SERIAL_RX 11 and SERIAL_TX 11. If you need to use both TX and RX pin, you should assign B10 to SERIAL_RX 11.

Enter this in CLI:

resource SERIAL_RX 11 B10

save

SBUS and UART Conflicts

Finally, if you use the SBUS pin, don’t use RX1, or you might get jittering in RC signal (your quad doing random things).

The SBUS pin is basically RX1 with an inverter.

Leave a Comment

By using this form, you agree with the storage and handling of your data by this website. Note that all comments are held for moderation before appearing.

14 comments

aumpak 30th December 2020 - 2:54 pm

Can you please help me on how to connect gps on this board?

Reply
Oscar 11th January 2021 - 3:45 pm

You can connect it to one of the UART’s.

Reply
Tripp Donnelly 23rd December 2020 - 12:09 am

you’re a life saver. How can I send you money?

Reply
Christopher M Burke 19th October 2020 - 11:46 pm

I can’t get osd to come up as I have my caddx vista wired to the soft serial “ie. Uart6” Now, if I go into cli and enter those commands Oscar, will my battery voltage and other osd info come up being that I freed that uart up after said commands? Its really annoying flying and not having my info where I can see it.
Regards, Chris.

Reply
Jani 1st October 2020 - 2:20 am

Wow.. that’s some serious marketing bullshit from BetaFPV. I wasn’t going to be using 3 UARTs for the current build, but when I saw free UART pads, of course I just soldered my crossfire to those pins assuming that I’ll just configure my crossfire to that UART, lol.

Only after the whole thing was built I went to the Betaflight to try to configure this thing and yeah… surprise surprise, there is no UART 6.

They should market those as GPIO pins rather than UARTs. Very misleading.

Reply
Jaybode 17th September 2020 - 6:04 pm

Oscar,
Interesting, I just purchased this board only because the site it clearly says 3 FULL UARTs
betafpv.com/collections/brushless-flight-controller/products/f4-2-4s-aio-brushless-flight-controller-12a-blheli_s
I wanted the full TX/RX PINs since INAV does not support PIN re-mapping.

I am happy now enabling Softserial and hooking up the GPS should work (from your post)
But assume under the hood it is a hardware UART (judging by the webiste listing 3 x FULL UARTS)
I logged support ticket and will let this page know the response. If its really soft Serial, then this is false advertising.

You have no idea how much your posts have helped me (and I guess many others) getting into this hobby – so well done.
Getting F.port working and understanding Inverted was a fantastic for me. All from you other posts.

When find myself on your pages again, I need to subscribe to your Patreon.

CHEERS!!

Jaybode

Reply
Vincenzo Tarricone 28th July 2020 - 11:54 pm

Hey Oscar, you saved me today and thousand other times.

Many many many thanks to you for your precious work!

Bye
Vincenzo

Reply
Stephen 9th July 2020 - 4:56 pm

Excellent. Looking forward to seeing if the betafpv 20A board with 1.25mm motor pins can support SBUS-RX + SmartAudio + RunCam-Device-Control.

Ability to start/stop runcam or caddx HD cameras from a switch makes it much easier to upload a video as we don’t have to cut the video down afterwards. Alternatively it opens up the option of running a GPS unit. Basically anything that requires a full TX/RX pair is difficult to implement on these boards currently.

Reply
Stephen 8th July 2020 - 6:15 pm

Thanks for the great info! I have the BetaFPV 20A 2.0 with the 1.25mm pin connectors and can see “S5” which I guess is pin B03 but do you know where pin B10 is on this board?
This is the model: betafpv.com/collections/brushless-flight-controller/products/f4-20a-aio-1-4s-brushless-flight-controllerblheli_s

Also it seems like RX2 is inverted to use for SBUS on this one?

Reply
Oscar 8th July 2020 - 11:17 pm

I just received this board as well, I will check it out in the next few days and make a review on it.

Reply
Utkarsh Verma 6th July 2020 - 7:27 pm

Motor beeper is set. I like the old school buzzer beeps, also comes in handy for low voltage warning. Thanks :)

Reply
Jeff Forhan 4th July 2020 - 8:19 pm

I actually got a response from their tech support on this issue. Here is what they said:

…” As the FC is updated, this UART6 is Softserial. Please map TX 11 to B03 and RX 11 to B10.”…

Jeff

Reply
Utkarsh Verma 3rd July 2020 - 8:48 pm

I have the very same board 12 A version. The issue I faced was that there are no buzzer pads, the ones shown as Bz+ and Bz- in the image in the post are +5v on my board. I could not figure out how to connect a buzzer to this one. Please let me know if any one has been able to do that successfully.

Reply
Oscar 4th July 2020 - 3:56 pm

If it doesn’t have buzzer pads, chances are you can’t use a buzzer. You can DIY, but you will need some additional hardware like transistor and resistor, not the easiest thing to do.
Alternatively you can setup motor beeper.

Reply