Problem with CAN-decoding

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drnicolas
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Problem with CAN-decoding

Post by drnicolas »

I am not veriy experienced with my PicoScope.

Today I tried to decode a CAN-Bus and was not successful so far.

Please see the attached screenshot


First, I see a lot of ripple in my measurement. Probe A is connected to CANH and GND, B is to CANL accordingly.

In the youtube-video about decoding CAN the signal is much better. is there something I have to configure ?

The decoded data is absolutely non-sense.

I also have problems to set the correct baudrate. My CAN uses 125 KBaud , which is not in the dropdown-list. Can I simply write the Baudrate into the field manually ?
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Martyn
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Re: Problem with CAN-decoding

Post by Martyn »

Try using a maths channel A-B and decode that, it will remove the common noise present on both signals.
Martyn
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drnicolas
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Re: Problem with CAN-decoding

Post by drnicolas »

Thank you. I will try tomorrow.

Can I also use 2 of the digital lines for decoding ? And what about baudrates which are not available via the up/down buttons?

In the meantime I had some succeess which means that for a short time I could decode standard frames but not extended frames

Martyn
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Re: Problem with CAN-decoding

Post by Martyn »

Digital lines can be used for serial decoding although the signals have to adhere to the specified voltage limits.

The baud rate can be entered in the box manually.

A Beta version of the software with improved decoding is due for release shortly.
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Mark_O
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Re: Problem with CAN-decoding

Post by Mark_O »

Martyn wrote:Digital lines can be used for serial decoding although the signals have to adhere to the specified voltage limits.
Dr. Nicolas, one of the great things about the Picoscopes, and being able to see the serial-bus signals in the analog domain, while still decoding them, is that you get to see what's happening... warts and all. Not after it has been 'sanitized' by threshold detection, which may vary between your test device and transceivers on the CAN bus.

In your example, the analog signals are very instructive. The CANL signal looks good. Proper amplitude and offset, with low noise evident. CANH on the other hand, looks problematic. The CAN signal is riding on top of a bias offset, has lots of noise spikes, and has really poor amplitude uniformity... especially toward the end where the CRC field resides.

These factors could make it difficult for devices on your bus to properly decode the data stream, not just PicoScope. This could result in a lot of bus errors, and retries. I'd see if I could confirm those problems on CANH (zooming in would help), and track them down and remedy them, before focusing on trying to decode the data itself.

- Mark

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