Unfortunately we have no experience without FrSky integration cable.
With this cable (wiring according manual) we have very same receiver working perfectly.

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Spirit System developer

OK. What exactly does the integration cable do? Is it a bidirectional inverter for the fport signal?

Yes, it is bidirectional driven logic converter with stabilized output.

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Spirit System developer

Thanks for your help.

After playing with this tonight, I have f.port working with the use of an integration cable.
The spirit is using 2 pins to communicate with the f.port receiver (full-duplex).

If an integration cable is required, then there's no real benefit of using f.port over sbus as the amount of connections to the fbl is the same.

For f.port receivers that have a non-inverted f.port, is it possible to use a single pin in half-duplex mode on the fbl to do f.port?

You'd need to implement non-inverted half-duplex communication on the fbl to allow this. It could be called: "FrSky F.Port Non-Inverted"

If this is possible, i'm happy to test on the Spirit and Spirit 2.

No, FrSky integration cable is not using full duplex.
You will have to buy Spirit GT where no FrSky integration cable is needed if there is problem using it.
With some receivers people were successful when using F.Port with very same connection. Your case if actually the first one where it does not work for some reason. Technically there is no reason why it wouldn't work with non inverting RX output. In any case we do not plan to support this unofficial route unfortunately.
What you wish is actually implemented in all units, except Spirit GT which has native support for SPort, FPort and FBUS.

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Spirit System developer

Are you sure you flashed F.Port to the receiver? because if you get it to work with 2 pin connection it sounds like in reality the receiver still talks SBUS/S.Port

The spirit2 is using 2 pins to talk to the fport receiver, the receiver only needs 1.

It doesn't work without an integration cable even with non-inverted fport connected because the spirit2 doesn't do half-duplex communication on a single pin for fport.

It does half-duplex for spirit GT, so its probably a hardware limitation, eg there's no hardware uart that can do half duplex comms that's connected to a output pin, or its just outside of the normal use case so not implemented on spirit 2 as everyone's using inverted fport signals on their receivers instead of soldering to the non-inverted pad.

Fport with an integration cable is kinda pointless. Its better to just use sbus + s.port + integration cable as the cable configuration is simpler.
The disadvantage is you'll have to unplug from the SYS port if connecting the USB dongle, but that's really not an issue.

I am sorry, but you are wrong.
Spirit is using Half Duplex for F.Port, there is no other possibility, because it will not work.
FrSky integration cable is using second pin to set direction of bi-directional transmission.

So please respect what I wrote. I designed these circuits.

There are many people that have Spirit Pro, Spirit 2 working with F.Port even without FrSky integration cable. But this is solution which we do not support nor recommend.
Same apply for S.Port actually where communication bus is almost identical to F.Port.

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Spirit System developer

Ah OK. That makes sense.

Which pin is half duplex, RUD ? Is there a weak pull-up enabled on the data line, or not? Maybe that's the issue and could explain why it works for some rxsr non-inv receivers and not others?

Edit: yes, I noticed that an fport receiver works when the spirit2 was set to sbus

No, it is AIL pin.

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Spirit System developer