Electronics > Projects, Designs, and Technical Stuff

CAN-bus msg validate, how?

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jhpadjustable:

--- Quote from: Jeroen3 on November 02, 2019, 07:53:36 pm ---To get your own interface you need the layer 1 tranceiver (eg: MCP2551) to get from a differential shared line to single ended split lines TX and RX.

--- End quote ---
For the lab, this might be good enough.

Chriss:
Ok.
I will give a try to read the CAN bus of one of my ecu flaher.
I never deal with CAN stuff on this level before.
What is the proper way to connect the logic analyzer to the flasher tool?
Do I need a 120 Ohm resistor first between CAN-H & CAN-L?
Do I have to connect CAN-H & CAN-L to the logic analyanalyzer?

Thank you. 

Jeroen3:
You are not going to receive anything useful is you do not have at least two CAN controllers on the bus.
Connecting only a logic analyzer will not work.
CAN will error not-acknowledge.

Yes, at least one 120 ohm is required for operation on your desk. In production each end of the bus requires the 120 ohm resistor.

Chriss:
Ok.
Here is my new idea how to setup a bench CAN simulator, will this work or not?

I have an Arduino Uno R3
If I buy this shield:
https://s.click.aliexpress.com/e/4qkMTal2
I found this ecu simulator on github:
https://github.com/AppSaloon/ecu-can-bus-simulator/blob/master/README.md

So, if I would all this stich together and connect lets say one of my diag tool like VCDS or maybe a better option the ELM327, could I use my Loguc analyzer and play with this gadget? Or I need something more?

Thanks.

Jeroen3:
ATMega based Arduino do not support this. You need a CAN controller.
Available in STM32F042K6, STM32F446 , LPC1768, AT90CAN32, PIC18F458 and many other. But not ATMega.

CPU -> CAN Controller  -> GPIO -> CAN Transceiver -> CAN Bus H/L.
Only the underlined bit is suitable for your logic analyzer. But a logic analyzer of little to no value with CAN bus, the signals are never wrong. The data is, and that is only visible in more complex software, like Busmaster.

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