Following [this](https://electronics.stackexchange.com/q/272336/64158) question, @curious_cat had more questions in comments that deserve a proper Q here:

>  Is there any standard encoding that has evolved on the digital encoding side? Just as 4 to 20 mA is de facto standard on the analog side especially in process control?

> So I wonder, in applications where rapid change is crucial, say airplane control, avionics etc. what sort of protocols have become the convention? Do they use 4 to 20 mA or PWM or dedicated buses?