CAN Device Sequencing on CAN Bus Question? Is there a particular order of devices?


#1

Wiring up Talons and assigning them addresses for the first time left us with several questions.
Is there a required sequence of devices? Rio > PDP > Talon? Rio > Talon > PDP? We were only able to get the Talon recognized by using the former, not the latter.
Does the CAN bus have to terminate in a resistor? We were able to get it to work with the PDP (and it’s resistor) in the middle of the chain.
Does the signal travel through a device when it is not powered? If the CAN bus runs through a motor controller without power, is the signal passed through?
We read several documents on CAN but were unable to discover (or understand) answers.
Thank you.


#2

No, they should work in any order, but the easiest way is usually to enable the internal resistor in the PDP using the jumper next to the CAN ports, and put the PDP at the opposite end of the bus from the RIO. Have you changed the CAN address on the SRX from its default?

Yes, CAN is designed for a resistor at either end, and that is the recommended way to do it. However, it is rather robust and will often operate in conditions beyond this.

As far as I am aware, all of the FRC CAN devices with two pairs of wires/ports have the two green wires/ports internally connected and the two yellow wires/ports internally connected, so the bus will still be complete even if the device is not powered.


#3

We were able to change the address but only with the wiring sequence above. Otherwise the computer would not recognize the device at the default address.


#4

I think I don’t understand.

If you changed the SRX’s address (using Phoenix Tuner, or last year’s Web-Based Configuration Utility), why would you expect to see it at the default again? After you changed the address, where you able to change the order?

In any case, other than having a poor connection, the only reason I can think why you wouldn’t be able to see the SRX in RIO>Talon>PDP, but be able to see them with the Talon downstream of the PDP is if the wire from the RIO to the Talon is too short. Did you cut those wires down?


#5

Sorry for the confusion. We were trying to change the address from the default but could not identify the Talon with the RIO>Talo>PDP sequence. When we switched to RIO>PDP>Talon, we could identify it and then change the address. We did not change the sequence back to recheck it due to time.
We definitely could have had a bad connection as the explanation. We didn’t cut the wires but were using WAGO splicers for the first time.
Thank you for the help.