CAN bus osciloscope signal

[milan87]

Hello All, 

I'm trying to learn something about CAN bus.

I created small program to send messages.

Hardware: USB-8502 NI-XNET usb-can deivce.

I get readings on oscilloscope, but I get also exclamation mark, which I don't know why occurred.

I set up oscilloscope properly, baud rate, thrash hold and so on...

Can someone share knowledge?

Could be that Oscilloscop isn't set ptoperly, but I don't know what.

Thank you 

[aeastet]

Did you open XNET and open the database file? You will need to do this before you run and LabVIEW code. When you open the database in XNET you will set up the baud rate as part of opening the file. If you do not do that you will not see any CAN traffic.

[milan87]

Hello, 

I have CAN frames on oscilloscope. Please check pictures in previous post.

Same signal I have when open a database in XNET, and also when I read it from memory.

Baud rate is set on 125k, and oscilloscope also. 

Signal is OK, but on end of frame I have exclamation sign '' ! ''.

My question is, why is there exclamation sign?

Best regards.

[GerdW]

Hi Milan,

---

@milan87 wrote:

Signal is OK, but on end of frame I have exclamation sign '' ! ''.

My question is, why is there exclamation sign?

Why don't you read the manual of your scope?

That's where the exclamation mark is shown - I guess the manual explains its meaning…

[deceased]

My guess is that there is expected another signal after the CRC checksum.

Been a long time since I looked at CAN, but from memory isn't it CRC-ACK-EOF

Sure someone with more recent experience can correct if i'm wrong.

0xDEAD

[milan87]

Yes, this could be solution, because I just connected CAN source on oscilloscope.

I don't have another device to receive frame, so ACK missing, because no device acknolage the frame.

I will get another device and give you feedback.