Odd behavior with errored messages

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JerryR
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Odd behavior with errored messages

Post by JerryR »

I am working on a project that has multiple CAN devices talking on the bus. It seems OK when not all the devices are on the bus; that is, I see no errors on the bus. However, when all of the devices are present I see the problem shown in the attached trace. The first message shown at left in the trace was fine. The next message has an error at the end. I am trying to understand the waveforms to understand what's going wrong here (it happens over and over) but I am wondering if someone can tell me what might have gone wrong with that second message at the end.

I appreciate any thoughts, tips, or help you can offer in understanding what is going wrong with my CAN bus.
It is terminated normally and like I said if I remove one of the devices, things are error free but with all the devices present, errors occur. I have tried to isolate by trying one device off the bus at a time but basically it works fine with any of the devices removed one at a time as long as not all of them are present. Any ideas?

I'm really hoping the waveform will offer a clue to someone who knows the CAN bus at the hardware level. Thanks!
Jerry
Attachments
End_of_msg_error.png

bennog
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Re: Odd behavior with errored messages

Post by bennog »

Can you post a .psdata file

Do you have duplicate CAN nodes in the network ? For example 2 nodes with the same ID.

Judging from the voltages in the message the message is rejected by multiple nodes. (crc error ?)

What is the length of the bus and topology, where are the termination resistors on the bus ?

Benno

Martyn
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Re: Odd behavior with errored messages

Post by Martyn »

Can you post a psdata file showing this capture, and give a description of the actual Can system you are testing.
Martyn
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bennog
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Re: Odd behavior with errored messages

Post by bennog »

Other question popped op looking at the image you posted.

Do all nodes use galvanic isolation between the bus ant their internal power, if not are all nodes powered from the same power supply ?

Benno

JerryR
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Re: Odd behavior with errored messages

Post by JerryR »

Thank you for the replies and questions.

The bus is configured as in the attachment.
I tried to attach the psdata data file but the file is 19 MB and too big to attach. Compressing didn't help either I assume because it is binary.

I do not believe the CAN interface points have galvanic isolation but I am looking into that now.
The power distribution to the nodes would be different for the display, the ECU (master) and the individual ECU nodes. All of the ECU's 1-24 are on the same power and I believe the ECU (master) is on that power but the display is likely on a different power source.

I have noticed that if I just power off the display the system is stable and has no errors. If I power it on and power off the ECU(master) the system is stable and has no errors. In neither of these power-off tests do I disconnect the equipment. It's still connected.

It is only when the display and the ECU(master) are both on that we see the errors.
Attachments
bus-layout.png
bus-layout.png (8.53 KiB) Viewed 12023 times

bennog
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Re: Odd behavior with errored messages

Post by bennog »

you can try a wetransfer for the .psdata if it is too big.

If the nodes are not galvanic isolated the you need to connect all the 0V signals of all the power supply's together.
Also make sure all nodes use extended addressing mode.

Benno

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