CAN Loop End Location

Technical Control System
1

So this year the CAN loop for our robot ends at the roboRIO and not the PDP, meaning that we would need a 120A breaker at one end. Do other teams have experience with attaching a resistor to this CAN wire or is there usually another method if the loop doesn’t end with the PDP and consequently the built in fuse there?

2

There should be two ends to the CAN. One of them is the RoboRIO, the other is generally the PDP. If it is not, then you would need to add a resistor in to terminate it. The Resistor is simple enough to wire in, just splice it onto each end of the green and yellow wire and then solder. Heatshrink over the custom circuitry. The RoboRIO and the PDP have this resistor built into themselves.

3

Our CAN bus wired up better with the RIO on one end and the pneumatic module on the other. That’s fine as long as the terminator jumper is removed from the PDP and a 120 ohm resistor is added to the CAN terminals on the pneumatic module.

4

We used/soldered this at the end of CAN to terminate:

https://www.playingwithfusion.com/productview.php?pdid=104&catid=1005

Again, like electroken said, switch the jumper on the PDP to “OFF”

5

How would you switch the PDP jumper to off?

6

Just pull the jumper off and put it back on in the off position.

https://frc-docs.readthedocs.io/en/latest/docs/getting-started/getting-started-frc-control-system/how-to-wire-a-robot.html#pcm-to-pdp-can

Note: The PDP ships with the CAN bus terminating resistor jumper in the “ON” position. It is recommended to leave the jumper in this position and place any additional CAN nodes between the roboRIO and the PDP (leaving the PDP as the end of the bus). If you wish to place the PDP in the middle of the bus (utilizing both pairs of PDP CAN terminals) move the jumper to the “OFF” position and place your own 120 ohm terminating resistor at the end of your CAN bus chain.

7

Probably a dumb question, is that something you’d do with pliers or is there a specific way to move it? Sorry if I sound ignorant I just don’t want to break anything

8

The jumper can definitely be moved with a small pair of pliers. I agree with your concerns about breaking things, though. Be careful not to snap any of the small pins.

9

Thanks! I just switched the jumper to off and put on a 120 ohm resistor on the end of the bus and it seems to be working

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10

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