Re: CAN-H and Vbatt Short

Hi Kees,

I am using TJA1040 CAN transceiver, And speed of the bus is 500kbps, 
terminated by 120ohms. When i do this CAN-H and Vbat Short communication 
is happening in proper. But some error frames are generating during short. 
and this error frames leading to "Error Passive" state.

Hi John,

2 nodes are connected in the bus but my device has only Tx messages. No Rx 
mesages from partner node.

This case is mentioned in the document "ISO 11898-2".

But first of all i want know whether this error will happen OR should n't 
happen. If it happen pls give me some reference..

Regards,

BoopathiRaja.G




"Kees Zagers" <[email protected]>
Sent by: [email protected]
18 - Dec - 2012 01:22 PM
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Re: [CANLIST] CAN-H and Vbatt Short






Sorry forgot one thing.

I presumed you have a CAN high speed transceiver chip. If you have a low 
speed transceiver chip and further low speed network and did the 
termination in the right way, the network should work with the shortend 
CAN Hi to battery.

Kees

----- Original Message ----- 
From: <[email protected]>
To: <[email protected]>
Sent: Tuesday, December 18, 2012 8:40 AM
Subject: Re: [CANLIST] 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
> 
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