Problem with CAN-BUS decoding

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janz
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Joined: Fri Jan 08, 2021 5:51 pm

Problem with CAN-BUS decoding

Post by janz »

One problem with CAN is that it is not a good word to search for in any forum so I hope I'm not duplicating another topic (I hope using CAN-BUS in a topic helps).

I use my PicoScope 3000 series for decoding decoding data in a CAN Bus. I can see that the bus is working because there is a device that shows the data on a display and there data is updatind al the time. But when I look at the data in Picoscope 6, most of the datapackets are reported with errors. Sometimes CRC, Bit Stuffing and Valid column are all wrong and no data is shown, sometimes only the Valid column shows cross. But even if everything is wrong, the display still shows that actual values. What I also notice is that most of the time, only one channel is properly decoded. It can be H or L, but (almost) never both.

Maybe it is just the way I connect the probes, but I wouldn't know what. Does anyone have tips on what to watch out for? A list of common mistakes (if they are common, I probably made them :) )

bennog
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Re: Problem with CAN-BUS decoding

Post by bennog »

Can you post a .psdata file (or link to some cloud storage with a .psdata)
An preferably can-h and can-l at the same time e.g. ch-A and ch-B

Benno

janz
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Re: Problem with CAN-BUS decoding

Post by janz »

No problem. A few observations.

Devices attached to the bus are one device that send a 0x37 message each second with temperature values in it. The other sends 0x36 messages with suspension values. Each second if there is no change, otherwise as as as the Arduino can send them. In the dataset attached, not one was seen as a proper message whereas the display showed the changing dat al the time.

I've tried some more myself, but I'm only getting more confused. Would me nice if yo could shed a light on it.
Attachments
20210111-0001.psdata
(767.08 KiB) Downloaded 2 times

bennog
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Re: Problem with CAN-BUS decoding

Post by bennog »

I have the idea you miss the start of the packet.
Can you set the trigger somewhat later so the whole message is visible.

Benno
Attachments
20210112-0001.psdata
(770.88 KiB) Downloaded 2 times

Martyn
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Re: Problem with CAN-BUS decoding

Post by Martyn »

I would suggest using an Advanced Trigger, Pulse Width with a time of 25usec, and set the position to 5% so that you always get the start of the message.
Martyn
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