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Identifying origin of messages on CANBUS

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zzattack:
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?

langwadt:

--- Quote from: zzattack 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?

--- End quote ---

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

capt bullshot:
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.

David Hess:

--- Quote from: langwadt on February 26, 2020, 02:18:01 pm ---stick a small resistor on the lines from C ? The voltage on C then ought to be slightly higher for messages from C
--- End quote ---

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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