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For example, CANBUS has two transmission lines CAN_HIGH and CAN_LOW. Polarity matters. Would the performance be affected if a polarity protection circuit with couple of diodes would be implemented?

Normally on the left side, when there is a voltage source, it doesn't matter it is connected +/-, output is + on the CAN_HIGH side and - on the CAN_LOW side. I just thought since input is High and Low(as a reference), it can be applicable but not sure.

enter image description here

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  • \$\begingroup\$ What do you mean with "polarity"? I don't see how diodes would protect you from connecting CANH to CANL or vice versa. Maybe you could post a schematic? \$\endgroup\$
    – Lundin
    Aug 26, 2022 at 11:13
  • \$\begingroup\$ @Lundin I have added the idea. \$\endgroup\$
    – alfonso
    Aug 26, 2022 at 11:26

3 Answers 3

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Both CAN data lines are positive with respect to 0 volts.

Low-speed data: -

enter image description here

High-speed data: -

enter image description here

Images from wiki - CAN bus

So, they don't need to have any polarity protection.

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  • \$\begingroup\$ thanks. I understood it wrong that like a voltage level, there is one high and one reference level. In this case a cable connection should be with correct polarization. That was the reason I thought polarity protection can solve this issue and provide flexibiilty of connection regardless how polarity is. \$\endgroup\$
    – alfonso
    Aug 26, 2022 at 12:01
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That connection doesn't make any sense. You seem to confuse polarity of a voltage supply with polarity of signal voltage levels. The ambiguous term "polarity" might be used in either case, but in case of supplies it means connect + to + and - to -. In case of signals it means active low or active high. There are absolutely no similarities except the name of the sloppily used term "polarity".

These are both signals of 2.5V +/- 1V. Strictly speaking it's actually the same signal but send on two lines; the difference between how the lines act are the voltage levels of the data and active low/high. Furthermore, they are semi-duplex signals, so currents might travel in either direction. You might want to study differential signalling.

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  • \$\begingroup\$ thank you very much. Yes, it seems I just understood to signaling part completely wrong. therefore, as I explained on other comment below, I had an idea to eliminate polarity on signal. Now, better understanding. \$\endgroup\$
    – alfonso
    Aug 26, 2022 at 12:03
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Polarity protection is significant in power supply circuits, you cannot use it in or should not use it in data transmission

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