There is a 4 pin header on most frsky X series receivers.
I have found this article] on Oscar Liang that ID's 3 of the pins on the X4R (the article is intended for finding the uninverted s.bus signal)
I am trying to figure out what the 3rd unidentified pad/via is for (perhaps uninverted s.port?)
Is that VCC for input? or output? What voltage level?
And is that 4 pin header the same use/pinout on all X series receivers that have it?
My goal is to interface my xsr to a Brain2 heli gyro without using an inverter cable, and then curiosity kicked in, too.
ORC is giving me an HTTP error when I try to upload photos, here are the links to pics that help (from Oscar's page, linked above)
![Image](https://oscarliang.com/ctt/uploads/2015/10/frsky-x4r-sb-subs-uninverted-hack-naze32-300x200.jpg)
![Image](https://oscarliang.com/ctt/uploads/2017/07/x4r-rx-uninverted-sbus.jpg)