How to do a "perfect listen" in CAN using NI boards?

[etrigo@embraer.com.br]

I wanna isolate the CAN boards from my bus, I mean the NI CAN boards can not answer in my bus to any equipament.

[EdDickens]

The question sounds much simpler that it probably is. If all you want to do is listen to the bus, then you would just configure the port, then use one of Read VIs to continuously read the bus, and close the port when finished.

I don�t think any of these VIs will produce any bus traffic, but I�ve never looked into this.

If this is not what you mean, please provide some more details on what you are trying to do.

Ed

[etrigo@embraer.com.br]

Dear Ed,

Tanks for anser my question. But let me try to explain my problem.

I have my "CAN reader" working properly, reading and saving all CAN data in my system.

But for some reason and I don´t know why my "CAN reader" makes my system work different, what I mean is:

I have a CAN controler in my system who send the messages to the rest of the system. If no one else anser the resquest of the controller, after some time my controller stop to transmit the messages and goes to hold(normal operation).

When I have my "CAN reader" listen the bus it doesn´t happens, so for some reason the "CAN reader" is talking with the controller and the only action it do is read the bus so this is my problem.

Best regards.

Eduardo Trigo.

[DiegoF]

Hi,

You are probably refering to reading from the bus passively. Even if the port is configured to read only, the CAN controller will acknoledge any frame.

NI just realesed the Series 2 CAN hardware that has the ability to disable the ACK to do passive monitoring on the bus. The CAN controller used in the Series 1 CAN hardware cannot disabled the acknoledge.

Hope this helps.

DiegoF
National Instruments.

[etrigo@embraer.com.br]

Thanks!!!

This is what I want....but how to do it in CAN series 2...

[DiegoF]

Hi,

With the Bus Monitor there is a check box that allows you to select listen only mode.

Programmatically, You would use the ncConfig in C (NC_ATTR_LISTEN_ONLY) or the ncSetAttr.vi with the 'Listen only?' attribute.

DiegoF
National Instruments.