Using a star configuation for Jaguars on CAN

[Dale]

For what it's worth, our RJ11s have have four pins installed and six channels, just like a normal teleco connector.

Hugh,
How did you get a good crimp on the cable with the round(ish) Ethernet cable? It would seem like with most of the wires removes the top part of the connector might not grab the outside shell of the cable very well. Did they tend to come off, did you do something special, or did it just happen to work?

Dale

[Hugh Meyer]

Originally Posted by Dale

Hugh,
How did you get a good crimp on the cable with the round(ish) Ethernet cable? It would seem like with most of the wires removes the top part of the connector might not grab the outside shell of the cable very well. Did they tend to come off, did you do something special, or did it just happen to work?

Dale

Dale,
It clamps down about like on a RJ45 network connector. We just try to push the outer insulation into the connector before making the crimp. Even if it comes out the wires are still securely held by the crimp pins deeper in the connectors.
Hugh

[DonRotolo]

Originally Posted by Dale

An active star module that allowed every jaguar to remain at it's default address of 0 would be very cool.

That would kind of defeat the advantages of CAN networking though (the added complexity of the "router")

But there is no reason CAN can't be used in a star topology. We use a star topology in the cars where I work, on both the 125 kb/s and 500 kb/s networks. The key is proper terminations.

Terminating resistors are intended to prevent the signal reflections that occur at the end of an open-circuited wire. What happens is the signal hits the open wire end (at the speed of light) and bounces back into the network (at full amplitude). Do this just wrong and your data bits turn into garbage.

A good tool to see if your star network is well-terminated is an oscilloscope. Compare a known-good signal to your network.

Regarding noise: A CAN-Bus is inherently resistant to noise, since it uses differential signaling. It is the difference between CAN-H and CAN-L that determines logic 0 or 1. In theory, both wires of the network will be affected equally by some induced noise, while the difference between the wires remains constant. In practice, the noise induced into each wire is "same" enough to work against noise very well.