>OK, thanks for the explanation.

You are welcome.

>How does this work out with EMI, cable lengths and termination?

Don't know. In our case the CAN was point to point for the second 
instrument, I don't know enough about the spacecraft architecture for the 
first instrument to know if multiple instruments were on the CAN bus, but 
believe this may have been the case.

>Is this the way a normal can driver works (passive drive to
>recessive state and active drive to dominant state)

Essentially yes, as I understand it. It may be that they have current 
source/sink in the driver chips, but I don't have a driver chip datasheet 
handy to check.

>I have been thinking of using this method to also automatically
>handle turnaround for RS485 nodes (switching between txing and
>rxing). That way turnaround would be handled automatically without
>the need of a TX enable signal but I'm afraid I will reduce maximum
>cable length and increase EMI susceptibility

Hmm, I am looking at using MCP2551 CAN transceiver chips for the same 
purpose for the same reason ...

The termination we used on the spacecraft instrument was 150 ohms across the 
differential pairs, and then 300 ohm full up and pull down to set the 
recessive state condition. This would have given pretty good transitions 
from dominant to recessive state, (the other end had the same I believe), 
and we were operating at 500kbs. So I suspect that with suitable 
terminations setting the recessive state, there would be no or little 
difference to active drive to the recessive state, unless running at very 
high rates that RS485 can go to. 

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