Author Topic: Identifying origin of messages on CANBUS  (Read 862 times)

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Offline zzattackTopic starter

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Identifying origin of messages on CANBUS
« on: February 26, 2020, 11:55:02 am »
I've got a CAN bus with, say, 3 nodes A, B & C, and I'm trying to emulate, say, device C.
First step in doing so would be to understand C's behavior, and therefore I want to isolate/identify messages originating from this node C. It's possible for me to intercept bus wiring at arbitrary locations, but I am not able to hook up to transceiver ICs without destroying the node in the process, so that's a last resort. Simply removing C from the bus and see what disappears does not help, as the other nodes are influenced by that. Is there a way to determine message origin on a bus like that?

Alternatively, by intercepting the bus wiring to C and putting a gateway in between both ends, I could control what comes in and goes out of C. Is that a reasonable way of going about this, or perhaps there's more effective approaches?
 

Online langwadt

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Re: Identifying origin of messages on CANBUS
« Reply #1 on: February 26, 2020, 02:18:01 pm »
I've got a CAN bus with, say, 3 nodes A, B & C, and I'm trying to emulate, say, device C.
First step in doing so would be to understand C's behavior, and therefore I want to isolate/identify messages originating from this node C. It's possible for me to intercept bus wiring at arbitrary locations, but I am not able to hook up to transceiver ICs without destroying the node in the process, so that's a last resort. Simply removing C from the bus and see what disappears does not help, as the other nodes are influenced by that. Is there a way to determine message origin on a bus like that?

Alternatively, by intercepting the bus wiring to C and putting a gateway in between both ends, I could control what comes in and goes out of C. Is that a reasonable way of going about this, or perhaps there's more effective approaches?

stick a small resistor on the lines from C ? The voltage on C then ought to be slightly higher for messages from C
 

Offline capt bullshot

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Re: Identifying origin of messages on CANBUS
« Reply #2 on: February 26, 2020, 03:09:41 pm »
You could try to build a CAN bus externder using one of these (or maybe even two simple CAN transceivers) to separate C from A and B:

https://www.onsemi.com/pub/Collateral/AMIS-42770-D.PDF

It's quite a long time ago I've used that chip, so I don't remember if it would fit your needs, please read the datasheet on your own to determine this.
Safety devices hinder evolution
 

Offline David Hess

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Re: Identifying origin of messages on CANBUS
« Reply #3 on: February 27, 2020, 07:43:08 pm »
stick a small resistor on the lines from C ? The voltage on C then ought to be slightly higher for messages from C

That could be made to work by detecting the direction of the signal which is indicated by the direction of current flow.
 


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