Connecting 2 CAN channels of a single ECU on the same CAN bus

[rsayyappan]

Hi,

I have a query on CAN bus topology.

Is it recommended to connect 2 CAN channels of a single ECU to the same CAN bus?

If then what would be recommendations on stub length and distance between stubs?

[Hooovahh]

The CAN 2.0 spec I believe is where this information is found.  That being said the standard is a bit strict and most of the time you don't need to follow all of the requirements for communication to work.  The spec says to have two devices on the bus with two 120 ohm resistors on each end.  Then when you add more devices they are to be something like 15cm from the bus in the middle between the two nodes adding no additional resistors.  That being said I've seen CAN work with 1 resistor, or zero at times, and the node length has worked with multiple feet from the bus before.  It all really depends on the amount of traffic, the environment, and the amount of dropped data that is acceptable.

[Minions]

Distance is also dependent on the cabling medium being used.  It is advisable to use shielded matched impedance cabling (120 ohm) with low capacitance (<25pf/lf) in order to maintain signal integrity without reflections.  See Belden 9841 cabling for an example.