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Can Bus Issue w/SN65HVD230

Paul Leslie90
Prodigy 10 points
Other Parts Discussed in Thread: SN65HVD230

First let me explain my setup.

1) I am using an arduino due to drive the SN65HVD230 transceiver.

2) I am using Collin80 due_Can library with the arduino.

3. I have 120 Ohm terminations on each node

4. I have pinned out all connections from the bus to the transceiver and all is correct

5. i have pinned out connections between transceiver and arduino due - all are correct

6. Transceiver works on CAN HS network at 125K

Now I will explain my issue. I am having some issues with my Can bus. The CAN traces I attached below actually turn on the node I need them to (Surprising) on my CAN HS bus but  I also have a line going to a CAN HS to CAN LS converter I purchased from EEPOD.com. We use these guys to make testers at my work so I know they are good and know their stuff. I know the CAN messages arent being transmitted on the bus like they should be based upon the Oscope traces below. The CAN_H and CAN_L signals should be going in the opposite directions when transmitting a "1" on the bus I believe. But from my device the square wave is going in the same direction and not opposite directions. In addition the CAN_H signal is a lower voltage change than CAN_L. I think this is why the HS network still works there is enough of a difference in the levels that it still sees 1's and 0's with the differential voltage. But I also think that this is causing the CAN HS to LS converter to not work properly. I am looking for any help on pointing me in the right direction of where to start troubleshooting to correct this issue.

  • 0
    TI__Guru 62920 points
    Hi Paul,

    This actually doesn't look too bad. The waveforms look strange because the recessive-state voltage is higher than the CANH high level. This means that when the bus is undriven it is pulled to the higher voltage, and in the dominant (driven) state both CANH and CANL are pulled to a lower voltage by the HVD230. The CANL voltage is still much lower than the CANH voltage, though, so it gives a big enough differential signal that the other nodes on the bus should detect a dominant level. (If the recessive level were in between the CANH high level and CANL low level, you would get the more symmetric kind of waveform that you expect. That isn't necessary for successful communication, though.)

    Are you having communication issues between the nodes? If so, is there a way to trace down which node is the one having trouble? One idea might be to look at the receiver output from each and verify that the logic levels match the intended bus state.

    Regards,
    Max