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Discussion and questions related to the course CAN Bus Communications Decoded
I'm wondering how the CAN network responds to devices being removed whilst it is powered up?
I'd like to run a small CAN switch board on a steering wheel for driver buttons/switches. Let's assume it is on a branch on the bus nowhere near the termination resistors.
If the quick release steering wheel has a four pin connector (CAN Hi CAN Lo +5V and Gnd) and I remove the steering wheel from quick connect and therefore CAN bus:
- how will the other CAN devices react? I assume as no new data is being transmitted by the CAN switch they stay at their previous values in the ECU, PDU etc
- when the steering wheel is plugged in again does the CAN switch just rejoin the network or does it need a reboot etc?
Normally its OK, but sometimes it isn't. You will need to do your own testing, with your devices. It's good that you are thinking of this issue. What does the receiving device do, remember the last position of a button or switch, or switch to a default when an expected messages isn't received.
Connections intended for hot pluging (such as USB) will often have the power & ground pins make contact before the data pins. You might need that for your CAN Switch board, so it's something to be considered.
I'm a long way off from being able to test (engine and cage are a few months away so just getting ahead of the wiring plan whilst I have some time).
I suspect I'll run a curly cord initially and then see what happens.
I've not seen this done at all, I'm wondering if others have implemented something similar previously.
Could I even source a curly cord with a twisted pair in it? Hmm...
This is all case specific based on the devices operability. FWIW, i've done similar tests on OEM vehicles to see how the vehicle will respond to a crashed network(or a network that doesn't allow any communication because I keep pushing Arbitration ID 0 on the network without delay). In OEM Land, this will put a car in limp mode with all sorts of faults, or entirely shut the car down. For your case, it will depends on the device that's looking for the information the Switchboard sends, and if there's timeout ability associated with it (a good example is Motec C series dashes have Timeout values, while an AEM dash does not.)
when the can switchboard is plugged back in, it'll be back up and communicating with the rest of the network like nothing ever happened