NI-CAN/LS2 card does not give acknowledge

[Theo ter Meer]

I'm testing a custom board with among others a PowerPC MPC565 with 3 internal CAN bus modules. This board communicates with a PC with a NI-CAN/LS2 card. On the PC I can either run a Simulator program (written in LabView) or the NI-CAN BusMonitor. The custom board always sends messages; the NI-CAN/LS2 card always receives messages.
If I connect the CAN bus and start both applications (the custom board and the Simulator or BusMonitor on the PC) the custom board keeps retransmitting the first message. I see that on the scope. To my knowlegde this means that the receiver (= NI-CAN/LS2 board) does not give an acknowledge. The strange thing is that the Simulator and the BusMonitor on the PC does acquire the data correctly: as well as
the ID and the data contents are okay. It's only the same message over and over again.
Now another strange thing: when I connect a second CAN module of the custom board to that same CAN bus, everything works as expected. This second CAN module only then acts as an 'acknowlegde generator'. If I send five different messages, all five message are received correctly by the Simulator or the BusMonitor.
When the second module is not connected, the transmit sequence is stuck at the first message.

Who knows how to solve this problem. Is there e.g. any way to turn on or off the NI-CAN/LS2 acknowledge? How is it possible that no acknowlegde is given while, at the same time, the message IS received correctly?

regards,
Theo.

[dhuff]

That sounds really strange, I didn't think the NI-CAN cards have the ability to go into listen mode (some other companies CAN cards are able to listen without acknowledging the message)

First, did you check the power jumpers? You can power each device internally or externally, which is selectable by a jumper on the board. (look at Appendix D & E of the NI-CAN User Manual)

Second, check the termination resistance, is it different for 1 port compared to the other, and is it correct? NI gives direction on how to replace the termination resistors of their cards. (look at Appendix D & E of the NI-CAN User Manual)

If you try these 2 and still get no change, I would call NI.