In this short video, I will show you how to set up the Agilent InfiniiVision 3000 and
4000 X-Series oscilloscope to perform eye diagram mask testing on a differential CAN
serial bus signal.
The first step is to download the various CAN mask files that Agilent provides on our
website.
These mask files are available at no charge.
After storing the appropriate files to your USB memory device, insert it into the scope's
front panel USB device port.
The next step in making this measurement is to probe the differential CAN bus.
Agilent recommend using the N2791A differential active probe.
Now also available is the special probe head adapter that can be used to directly connect
this probe to a connector.
For our demonstrations, let's first look at a CAN signal in a standard non-eye diagram
format using a standard Agilent 4000 X-Series DSO and then we'll perform the eye diagram
mask test.
Here we show the scope triggering on ID 025.
For this measurement, we have probed this signal with our differential probe such that
the scope displays dominant-bit low.
The first thing to note here is that we are seeing various dominant bit low amplitudes.
The bits that are going the lowest are acknowledge bits.
The bit that you see near the middle of the scope's display is evidence of arbitration
between two nodes in our system.
Although we can't see it yet, there are also some timing shifts associated with these particular
bits since they are being generated by asynchronous nodes.
But an eye diagram test will overlay all bits on top on one another to show us all amplitude
and timing variations.
To execute an eye diagram mask test, we'll begin by pressing the save/recall front panel
key.
Next, select recall and navigate to the appropriate mask file.
In this case, I'm going to recall a 500 kB/s mask file based on dominant bit low probing.
When you recall this file, the scope will automatically set itself up to randomly capture
and overlay every differential bit of every CAN frame based on a unique clock recovery
algorithm that emulates worst case CAN receiver synchronization and sampling.
With all bits overlaid on top of one another we can now see worst case amplitude variations
as well as timing jitter.
But the jitter that you observe the CAN eye is not the typical random timing jitter you
see in most other eye diagram displays.
Most of the apparent timing jitter you see in this measurement is actually worst case
propagation delay of the CAN signal travelling from one end of the network to the other and
then back again.
During testing, if the signal crosses through any part of the pass/fail mask test region,
failures are clearly marked in red as you see here.
Also, take note of the fast update rate and mask test statistics.
This scope is capable of testing over 200,000 waveforms per second.
To learn more about Agilent's new InfiniiVision X-Series oscilloscopes, contact your local
Agilent distributor and ask for a demonstration.
Thank you!