Test and Measurement Forum

Problem with CAN-decoding

Forum for discussing PicoScope version 6 (non-automotive version)

Problem with CAN-decoding

Postby drnicolas » Sun May 10, 2015 11:07 am

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 ?
Attachments
20150509-0001.pssettings
(5.5 KiB) Downloaded 91 times
20150510-0001.jpg
drnicolas
Newbie
 
Posts: 0
Joined: Tue Dec 25, 2012 3:08 pm

Re: Problem with CAN-decoding

Postby Martyn » Sun May 10, 2015 8:45 pm

Try using a maths channel A-B and decode that, it will remove the common noise present on both signals.
Martyn
Technical Specialist
Martyn
Site Admin
Site Admin
 
Posts: 2352
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Problem with CAN-decoding

Postby drnicolas » Sun May 10, 2015 8:50 pm

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
drnicolas
Newbie
 
Posts: 0
Joined: Tue Dec 25, 2012 3:08 pm

Re: Problem with CAN-decoding

Postby Martyn » Thu May 21, 2015 12:27 pm

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.
Martyn
Technical Specialist
Martyn
Site Admin
Site Admin
 
Posts: 2352
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Problem with CAN-decoding

Postby Mark_O » Sun Aug 02, 2015 11:58 pm

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
Mark_O
Advanced
 
Posts: 44
Joined: Fri Oct 03, 2014 5:58 am


Return to PicoScope 6 for Windows

Who is online

Users browsing this forum: No registered users and 0 guests