Zero Bus Load On Transmit In NI Bus Monitor

[jkerrigan12]

Hi,

I am trying to read bus load when transmitting frames over a CAN bus using NI-XNET bus Monitor, but until I turn on the "log transmitted frames" option in the interface and database settings dialog I do not see any bus load. This does not make any sense to me. How can we have zero bus load if I am transmitting frames on the bus every millisecond. Does the NI bus monitor only register bus load on read frames?

I am using a PXI chassis with an  PXIe-8840 embedded controller and PXIe-8510 card as my XNET interface.

Also I am trying to implement the same bus load monitor as NI-XNET bus Monitor into my own labview vi's because we wont have NI MAX on every distributed machine but I cannot seem to find any examples of this. Can anyone point me in the right direction?

Thanks

[JefeL · Accepted solution]

Bus monitor can only calculate the bus load based on the frames that it is able to read.

We don't currently have any examples for the calculation but you should be able to reasonably predict the amount of time each frame requires for transmission. The CAN spec details how many bits are in a frame and when bit stuffing occurs. With that information you will know how many bits are actually being transmitted in a given period and can calculate the approximate bus load.