CAN Nodes and Termination question!!!

I have a question concerning the line impedance of Can bus. Currently we are communicating from an ECM to a Cluster with CA protocol. Each ECM and Cluster has a 120 ohms resistance inside for the impedanc termination. We are communicating at 250 kbauds on a really short distance, like 1 or meters.

Sometimes we branch a laptop on the bus to make a diagnostic.

The question is: When nothing is branched in the diagnostic plug, do w have to branch a 120 ohms resistance or we can lets it free.

Second question: Does the nodes for the diagnostic plug have to be exactl at the same distance on the bus, or one (CAN_H) can be closer of the EC and CAN_L closer of the cluster

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There is no such thing. CAN is commonly used through a pair of wires with unspecified line impedance.

This is not right. There should be just two terminators at the farthest points of the bus.

You should not worry about anything at this kind of distance.

Leave it open.

It doesn't matter at 1..2m cable length.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

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Vladimir Vassilevsky

My understanding was that CAN was to be run through twisted pair cable with a 120 ohm characteristic impedance. A quick google found this primer by TI that mentions the same on page 16:

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Of course, for his app, I can't imagine it'll matter in the slightest.


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