Re: CAN-H and Vbatt Short

Hello BoopathiRaja.G,

The CAN controller can have 3 states:

Error Active (normal, Rx cnt < 128; Tx cnt < 128)
Error Passive (Rx cnt > 127 or (Tx cnt > 127 and Tx cnt < 256)
Bus Off (Tx cnt > 255)

So your node is not in the Error Passive mode, but in the Bus Off mode. 
It will not recover from that, until a hard reset takes place.

It is logical that it comes directly into the "Bus off" state when you 
shorten the CAN-Hi to the battery. It will try to send a pattern of 0's 
and 1's, but it will read back all 0's. CAN-Hi minus CAN-Lo will allways 
be more than 2 Volts in difference, so everytime it does a retry of the 
first message an error occurs; 32 retries and the controller goes 
bus-off.

Hope this clarifies your situation.

Kees Zagers

PDE-Elect - Software Team 1 schreef op 18.12.2012 07:01:
> Hi Techies,
>
> I am facing one issue in my CAN-physical layer design.
>
> I am using Fujitsu micro. I have a CAN messages only for Tx from my
> micro. No Rx messages for my system.
>
> When i am shorting CAN-H line and Battery voltage(11V to 14 V) line,
> my controller generates the "Error passive" error.
>
> Why this is happening.? And my design validation team doesn't agree
> this point.
>
> And then Error Passive doen't recover back to Error Active State even
> if i removed the Short.
>
>  Pls help me out Is there any protection circuit vailable to avoid
> "Error passive " State. Or If it happens in protocol suggest me some
> documents for reference..
>
> Regards,
>
>  BoopathiRaja.G

--
Archives and useful links: http://groups.yahoo.com/group/CANbus
Subscribe and unsubscribe at www.vector.com/canlist/
Report any problems to <[email protected]>