NI USB-8437 bit rate

[Rick2]

Hi,

I am trying to set up a CAN bus monitor with the USB-8473 product.  

I can not see anything.  I have configured a microcontroller-based board as a node on the CAN bus.  I need to match the timing requirements for bot the uC and the NI USB-8473 board.  

I don't understand the difference between baud rate and bit rate.  

I have set my micrcontroller to the following bit rate settings: 

CAN Bus Bit Rate: 125 kbps

CAN Bus Clock : 40Mhz

BRP = 32    (BRPreg=31)

TSEG1 = 4

TSEG2 = 3

BT = 10

Triple Sample Mode

I program it to continually send a message on the CAN bus from Mailbox 0, with a certain ID, etc.  

In NI's MAX (Measurement and Automation Explorer) I set up a bus monitor as follows: 

In My System ->Devices and Interfaces -> NI-CAN Devices -> USB-8473 ->CAN0

In properties I choose "Edit the Segments of the Bit Timing Register" 

I select: 

BRP+1 = 6

SJW+1 = 1

TSEG+1=5

TSEG2+1=4

Triple Sample Mode

This results in a Sample Point of 60%

I have added a 150 ohm termination resistor on the CAN bus wire.  

All this results in 133.33 kBaud.

So, what am I doing wrong?  I can't see anything on the CAN Bus Monitor.  

What is the difference between kBaud and kbps.  

How do I set the timings of the two nodes the same?  

Thanks,

Rick 

[Matthew-B]

Hi Rick,

If you have some 120 ohm resistors, I would put it on the extreme ends of your CAN bus. This KnowledgeBase article talks about the proper termination of NI-CAN hardware.

What is your microcontroller? It looks like your microcontroller defines some settings differently than our hardware and knowing what all the abbreviations mean would help us figure out what the settings need to be.

In addition, is there data transmitting on the bus (i.e. if you scope the lines, can you see the voltage changes)?

Best Regards,