Re: So...
"Because those systems do have business being on the same bus."
No they don't. I can see that you might want a one way data signal from the ECU etc to the display system of the car, but there is no reason to have unrestricted bidirectional data flow.
I can't think of anything that would want to be displayed that couldn't be gathered from:
- A GPS receiver.
- A unidirectional stream (i.e. rev counter, TPS readings, error codes)
There is nothing that needs the radio to talk to the ECU.
Biting the hand that feeds IT
