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CAN Bus Off problem

hello all,

I am having a problem with the Bus Off testing procedure.

I have set the CANalyzer in listen mode. It is not tranmitting anything. My ECU is transmitting only one frame. The communication is normal. When I short the CANH and CANL pin with a wire, the CAN goes in Bus Off and when I remove it, it recovers properly. So the everthing is proper. Now my observations are:

When I short the CANH to CANL for a longer duration, say 1 sec. I am not observing any CAN error frame on the CANalyzer. The ECU goes into Bus Off and communication stops for that duration and as soon as I start again, I get the correct frame on CANalyzer. Is this the expected behavior or I am doing something wrong?? If it is expected behavior, please tell me why there are no error frames.

Does it mean, when bus is shorted there will not be any kind of frames on the Bus?? Not even error frames ???

As per my understanding of CAN, Before the error counter reaches to

256, for every error I shuold receive one error frame on the bus and counter should increment by 8. So when first time the ECU goes into bus off, I should atleast get 256 / 8 = 32 error frames on the CANalyzer. but thats not happening.

Please help me out.

Reply to
Achilles
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Yes - if the bus is physically shorted, no signal of any kind can get through. The CANalyzer sees nothing until you remove the short.

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Jim Nagy
Elm Electronics
Reply to
Jim Nagy

Hey...

now, I am not shorting the bus physically. I am using a CAN Stress tool, to induce the error in the ECU transmission. After sometimes, the ECU goes into the bus off. And the CANalyzer is in listen mode. I am observing error frames continously on the CANalyzer trace window. I am not sure why the error messages should come on bus. When the ECU goes into Bus Off, I stop all the communication in the software for

1000 ms. And then reinitialize it. So as per my understanding, During those 1000 ms I should not receive any error frames.....

am I correct ?? or soemthing else is expected ??

Reply to
Achilles

Hai

You get error messages if you are transmitting the messages from the CANalyzer, when bus off is induce by using the CAN Stress as the CANalyzer does not get any acknowledgment for the transmitted messages. Is it the right situation your getting error frames?

Rajesh Maddukuri

Reply to
raj

I hope that you should get the error messages irrespective of type of Bus OFF induce. As the ECU starts transmitting the error frames if it does n't get ack for the transmitted CAN messages

Reply to
raj

we won't get any error messages if the Bus is open rather than short.

Reply to
raj

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