CanCabling

Some rules on how to design a CAN network. Consider reading ProblemSolvingQuestions.

The rules are general and valid for an CAN network including CanOpen and DeviceNet. Therfore look at DeviceNetCable too.

Always use twisted pairs for CAN_H? and CAN_L?
Maximum cable length is between the two farthermost nodes on the CAN bus line. Remember, in the worst case a signal has to travel from the node at one end to the node on the other and of the line. It is a function of the bit rate as follows:

bit rate	max cable length (in m)
1Mbit/s	25
800Kbit/s	50
500Kbit/s	100
250Kbit/s	250
125Kbit/s	500
50Kbit/s	1000

(Table from CiA DS 301 4.02 page 20)

If you ask for a formula? There is one rule of thumb:

 cable length < 40000 Kbit/s * 1 m / BitRate? in Kbit/s

BitRate? given in Kbit/s as well. Using this, results in <40m for 1Mbit/s or <320m for 125Kbit/s. In this formula a typical transceiver propagation of 25ns and a typical cable propagation of 5 ns/m is used for calculation.

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