FrSky inverted signal – what is the point?

[Terje]

Been playing with a F4 flight controller (Omnibus F4 PRO). A real pain to work with when using the X4R-SB or XSR. The F4 chip apparently only has one inverter (on UART 1).

The workaround is to either use an inverter on telemetry (which I have not been able to get to work) or circumvent the hardware inverter on the receivers.

But what is the point with these inverters in the first place?!?

[jihlein]

Actually the F4 has no inverters on the MCU, the inverter is part of the board layout. I’ve seen various F4 boards with the inverter on Uart1, Uart2, or Uart3.

I believe the first RC manufacturer to offer SBUS was Futaba many years ago. Why that was an inverted signal I don’t know, but other suppliers these days copied it, and FrSky even went as far as using the inverted logic for Sensor Hub and S Port telemetry. I agree, it is a pain.

This link has probably the clearest directions for bypassing the S Port inverter and making it a non-inverted signal that I’ve seen.

https://blck.mn/2016/06/smartport-the-frsky-xsr-and-betaflight/

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