How to send data from flight controller to another mcu using serial port?

I’d like to send data such as rpm using serial port following the instruction,
but it did not work like this,
Which serial port should I use, did I need to set the serialx_protocol? Thanks
I do not like to use mavlink

Using Mavlink is a lot simpler.

Hi, the other mcu could not use Mavlink! Thanks

I used hal.uartB->begin(57600) and hal.uartB->write(10), it worked.
Maybe Mavlink was more simpler and better, I would try it later, thanks

Thanks for posting your findings.

@talos is this the only code needed for this? Or have I something to add (includings etc.)?