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Products => Test Equipment => Topic started by: Oze on October 25, 2021, 08:26:30 am

Title: Signal integrity on CAN-Bus - Eye Diagram and Eye Mask
Post by: Oze on October 25, 2021, 08:26:30 am

Hello everyone,
I am a long term viewer of the EEVBlog but finally I need the help of this awesome community. I'm currently struggling with the measurement of the signal integrity of a low speed CAN-Bus network (125 kbit/s).
I want to measure the signal integrity using an eye diagram on my Oscilloscope (R&S RTB2004). Therefor I've connected a differential Probe on the CAN-H and CAN-L lines and activated infinite persistence on my Oscilloscope. I got a beautyful eye diagram on screen but now I don't know how to determine if the siginal integrity is still ok because I don't know where to get an Eye Mask for the CAN-Bus with 125 kbit/s. So can anyone provide a way how to determine the shape of the valid region so I can determine if my signal integrity is ok or not?

Thank you so much

Oze

Title: Re: Signal integrity on CAN-Bus - Eye Diagram and Eye Mask
Post by: thinkfat on October 25, 2021, 08:34:26 am

You need the recovered bit clock as a trigger, otherwise it'll be just a pretty picture on the scope screen.

Title: Re: Signal integrity on CAN-Bus - Eye Diagram and Eye Mask
Post by: dietert1 on October 25, 2021, 09:01:52 am

I think CAN is an application of RS485. https://www.ti.com/lit/an/slla375/slla375.pdf (https://www.ti.com/lit/an/slla375/slla375.pdf) has some introduction.

Regards, Dieter

Title: Re: Signal integrity on CAN-Bus - Eye Diagram and Eye Mask
Post by: Leo Bodnar on October 25, 2021, 05:38:56 pm

If you have access to one of the devices, trigger on the signal going into CANbus phy (TX line)
Leo