NI-XNET C API for CAN Loopback Test - No Baud Rates Above 125k Work

[whoisjohngalt]

Using the NI-XNET C API Loopback Test Example, baud values of 125k or less work as expected receiving exactly what was transmitted. Whenever I change the baud rate in the CAN database to any value above 125k baud, the loopback no longer works (received payload is all 0's). 

Driver used: NI_XNET 20.0

Hardware used: USB-8502

Using this Example Visual Studio Project:

C:\Users\Public\Documents\National Instruments\NI-XNET\Examples\MS Visual C\CAN\CAN_Loopback_Test

Using this Example CAN Database:
C:\Users\Public\Documents\National Instruments\NI-XNET\Examples\NIXNET_example.xml

I tried setting the following properties as well to no avail: nxPropClst_BaudRate64  nxPropSession_IntfBaudRate64

[kayfh · Accepted solution]

Hi,

you need to add termination to your CAN bus, either with external termination resistors or by setting the XNET Termination property to enabled on your two sessions before writing anything.

[whoisjohngalt]

Thanks that solved it! Should have read the comment at the top of the file.

// Please make sure that the bus is properly terminated as this example does not
// enable the on-board termination. Also ensure that the transceivers are
// externally powered when using C Series modules.

[Semaren979]

Hi.

I have the 120Ohms resistor externally but, I still having the timeout. My usb8502 is one port only, should be this the issue? What is wrong? Thanks 

[Hooovahh]

You should make your own post. If you are new to CAN you should checkout my CAN Blog.

https://hooovahh.blogspot.com/2017/03/can-blog-introduction-and-downloads.html

[whoisjohngalt]

Does it work for you at lower speeds?

[Semaren979]

Yes. I am new in CAN. That i why I am looking for answers to help me to understand. Thanks for the blog link I will read it all.Thanks 

[Semaren979]

This is what I got from LabVIEW and the CAN 120ohm termination. is it ok?

Thanks 

[Hooovahh]

The example you showed will write on one port, then read it back on a second port that is wired together.  You only have one port, so I'm not sure what you were expecting to happen.  It timed out because it couldn't read anything.

[Semaren979]

Hello.

Yes Hooovahh. At the beginning I was thinking about the second port but, I was expecting to see some response once I plugged the 120Ohm. As you may know I am a beginner and i am trying by practically to understand what is happening with this example. But It seems that it does not work. So, until I have a second port I will see the final response.