That’s in the Arducopter Wiki: The protocol supports up-to 24 ESCs, but ArduPilot’s device driver implementation currently limits this to 12. Connect the TLM telemetry output from the ESC to the serial RX of your flight-controller. The signal-pins S1 , S2 , S3 , S4 from the ESC are used to receive the commands from the flight-controller, so the serial TX from the flight-controller must be connected to every signal-input in parallel.
But if passthru isn’t working for the configurator then the Wiki does need an update. But mention of a USB Serial adapter is in the Wiki.
I’ve been loosely following this, have at least skimmed most of the posts, and I’ve taken a look at the documentation. My takeaways so far:
I wonder if setting DSHOT1200 actually broke an already broken configuration so badly that you were actually using standard PWM fallback, causing the observation that “it worked.”
The serial (one wire) protocol is almost certainly the intended (and likely superior) connection method.
Nothing leads me to believe there was an expectation of a lack of ArduPilot users.
The documentation sources definitely reference wiring method and it reads clearly to me anywhere that it’s described. As Dave says, if passthrough is broken for AP, we should amend that portion in the AP wiki.
USB is not a fixed rate protocol. Downstream peripherals sometimes require setting a baud rate, but often, serial devices connected via USB are auto-bauded anyway. You may be setting a value in that dropdown that actually has no effect on the hardware in use, though its inclusion in the UI indicates that it may be required to be explicitly set in some use cases.