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I have found this circuit from http://vector.com/portal/medien/cmc/application_notes/AN-AND-1-106_Basic_CAN_Bit_Timing.pdf

Oscillo CAN

Please can someone explain to me what is the negative connection of the oscilloscope : does it mean the GND ? Thanks in advance :)

Pss the oscillo is Tektronic MSO 2024B: Mixed signal oscilloscope

enter image description here

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2 Answers 2

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If your scope has math functions you can connect a second input to the negative line and choose something like 'A minus B' for your trace.

That is to say, you don't use a dedicated negative input. You use another normal input connected to the negative side of what you're measuring, and you go to math functions and look for the setting to subtract one input from the other and draw that on the screen.

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  • \$\begingroup\$ Where is the negative line ? The oscillo is Tektronic MSO 2024B: Mixed signal oscilloscope \$\endgroup\$
    – The Beast
    Dec 4, 2016 at 20:18
  • \$\begingroup\$ In accord this sh1, you need to use two probes, one as "positive", and another as "negative". Then subtract. \$\endgroup\$
    – Ale..chenski
    Dec 4, 2016 at 20:43
  • \$\begingroup\$ So the positive here is CAN_H and the negative is CAN_L right ? They are normal probes ! \$\endgroup\$
    – The Beast
    Dec 4, 2016 at 20:52
  • \$\begingroup\$ @Frankenstein, Actually, in that diagram it looks like CAN_H is negative. I don't know why. Just plug them in and see. You can switch them later if you have to. \$\endgroup\$
    – sh1
    Dec 4, 2016 at 20:59
  • \$\begingroup\$ @sh1 To sum up: one channel should be connected to CAN_H and the other one to CAN_L. Also the oscillo GND should be connected and then I checked that it has also Waveform Math so I will look on how to use it. Many thanks :) \$\endgroup\$
    – The Beast
    Dec 4, 2016 at 21:00
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Apparently the application note assumes that the oscilloscope must have a differential probe input. In this case they offer a simplified recipe to look at CAN signaling and determine its bit rate. But they forgot to tell you this.

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  • \$\begingroup\$ So the differential probe input is the negative connection they are talking about. Please see the osscilo picture. \$\endgroup\$
    – The Beast
    Dec 4, 2016 at 20:22
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    \$\begingroup\$ You need a differential probe for this task like TDP0500 or P6251, tek.com/sites/tek.com/files/media/media/resources/… . Or use two probes, as sh1 suggested. \$\endgroup\$
    – Ale..chenski
    Dec 4, 2016 at 20:46

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