[SOLVED] CAN Communication: Knowing Which Node Transmitted Data

CAN Communication: Knowing Which Node Transmitted Data

I am new to CAN communication and one of my tasks is to use a CANalyzer to learn what message IDs are being used for a product and what data is being sent/received.

The product has multiple nodes that can send/receive CAN messages. I know CAN messages are broadcasted to all the nodes, but the part I'm having a hard time determining is which node transmitted the message and which nodes received it.

So, for example, if I have 3 CAN nodes, is there a way I can determine that Node 1 sent the message and Node 2/3 are receiving the message?

Thank you in advance.

Solution

Generally, you can't know this by listening to the CAN bus alone. The same old story whenever someone asks about data on "CAN bus" is: what application layer protocol is it using? "CAN bus" doesn't tell you jack, it's just the specification physical and data link layers. The concept of identifying individual nodes does not exist on the data link layer, only on the application layer.

There's two possible ways for you to tell:

If you know the application layer used on top of the physical CAN bus and know that it uses node id, then you can tell which node that is sending what data by decoding the application-layer protocol.
On each node, you can sniff the Tx signal between the MCU and CAN transceiver with an oscilloscope. That one only goes active when a node is sending or ACK:ing. Most modern scopes has a CAN frame decoder feature, saving you the head ache of decoding the frames manually.