Cable & Connectors for CAN bus

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- Eric Anderson
  
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posted
17 years ago

Wed, Jul 26, 2006 1:08 AM

Is there a standard for CAN bus cable? Are there limitations as to the cable and connectors to be used? I know that Vector Cantech uses DB9 connectors. I know of someone that is contemplating to use RJ11 connectors and the cable typical cable used for those connectors. It would appear that the cable should have a characteristic impedance of somewhere around 120 ohms since that is the termination resistor that appears to be recommeded.

Can anyone direct me to further information on the subject or tell me their experiences or thoughts?

- T
- Tim Wescott
  
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posted
17 years ago

Wed, Jul 26, 2006 4:08 AM

The CAN standard, by itself, doesn't specify the physical medium to be used. Anything that can be made to be passive 0, whether it be a twisted pair, a line on a board with open drain drivers, foghorns, or the level of beer in a trough, can all be used as physical media with suitable transceivers.

The limitations are the aforementioned passive 0 property, and a baud rate limitation that's determined by the speed of information propagation in the chosen medium and the length (beer in a trough performs much more poorly here than twisted pair).

There is an SAE standard for one particular CAN bus that specifies the electrical bus. It's the one most often designed to by 'CAN transceivers'; it calls out a twisted pair with resistive termination, a '1' is no differential voltage and a '0' happens when one or more transceiver is driving the pair.

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Tim Wescott
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- dalai lamah
  
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posted
17 years ago

Fri, Jul 28, 2006 10:44 PM

Un bel giorno Eric Anderson digitò:

Yes, 120 ohm balanced twisted cables, see ISO 11898.

My experience is that in most cases automotive wirings don't use expensive cables; any twisted cable is just fine, even at 1 Mbps. Probably the expensive cable is necessary when you go near to the limits of CAN bus specifications; the common automotive wirings are far less critical.

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asd