Protocol decoding is what we're talking about in today's episode of the 2-minute
guru and thanks for tuning in. Let's take a look.
This video's the extended cut of last week's two minutes on protocol decoding.
It is also the last episode of season one. We will kick off season two later next year and
next week we're going to kick off the Keysight oscilloscope webcast series.
More on that at the end of the video. Also recommended is this video on how digital
channels work on your oscilloscope from two weeks ago.
So, first let's talk about how to set up your signals. I'm hooked up today to a
CAN bus using analog channel one. A CAN bus is pretty straightforward. There's
only one channel, but if you're using a protocol that has more channels, consider
also using a mix of your analog and digital channels. If you expect to maybe have
trouble on one of your channels, use the analog channels for that, and then
digital channels for signals you're less concerned about. Protocol signals can
also be single-ended, meaning there's only one channel with data. Or they can be
differential, meaning they have two channels with opposite data. So, consider
using a differential probe if you're using a differential bus.
Once you are physically connected to your signals, you're gonna want to turn
on serial decoding. I'm going to hit the dedicated serial button and that's
going to turn on my decoding and I can see along the bottom, I have a
packet view of what's going on with this signal.
The next thing you're going to want to do from this is make sure your
thresholds are set up correctly so I'm going to use my trigger knob and make
sure that my thresholds are right in the middle of my bus there and
that means when I'm sampling my threshold is going to be appropriate.
Then once your thresholds are set up, you're probably going to want to change
your trigger.
This scope has a built-in hardware trigger for protocol built into the ASIC.
I get the trigger button, and let's change my trigger from an edge trigger,
which is how my scope booted, to a serial trigger. I'm going to select
serial down here and then I'm going to trigger on a start of frame and now you
can see my packet has stabilized on the screen and I have packets coming through.
There's other options here you can see this whole list of different triggers
that I have available for a CAN bus. Those options are going to look
different for different protocols, but one thing that's really helpful on these
scopes is the error
frame trigger. This means the scope is going to trigger every time I get an
error.
It's worth noting that you probably don't want to set it to trigger on an
error right away unless you're seeing errors on your system.
Let's go back to a start frame trigger and you'll notice that there's a
lot of dead time on my signal here between packets. So, one thing you can do
is use segmented memory to just capture packets and that's going to let you
capture a lot more information on your scope. So, let's go ahead and set that up.
I'm going to first scale into one packet and I have a full packet on screen. And
then i'm going to go to a acquire, then segmented. For my number of segs, I'm just
going to set it to the maximum number of segments and then I'm going to turn that
on. That's going to go through and only capture and store the data that is
around the trigger point so that eliminates all the dead time and I'm not wasting my
memory space with that dead time. You can see now it captured a thousand
segments of my signal
and you can see that I have actually captured over two seconds of data, which is
a thousand different packets of information. You're not going to be able
to do that on any scope with traditional memory. Segmented memory is great for
protocol decoding. You can even set up to trigger on errors and capture a thousand
different errors over time
Once I've capture this information, I can then go ahead and analyze my data so I
can just click on different segments using the touchscreen and I'm going to
go straight to those packets. Another way to analyze data on a scope is using the
lister and the lister is essentially a table of information and the scope's going to
go through and analyze all my segments and put together a list of packets in
time with time tags and I can go through and see how my system is working. So that
took about 15 seconds and I can scroll through and see my list of data and I
saw an error in there, so I'm going to click on this error and I have now pulled up
this error on my screen and I can see that this error happened at 2.3 seconds.
It was missing an acknowledge and this tells me there's potentially something
wrong with my system. So, I'm going to go back into normal memory mode and we're
going to trigger on
errors. So, I'm going to hit trigger and I'm going to trigger on all errors and
that's going to pull out a list of errors and I'm just going to zoom out in
time and see what we get.
If I pull up my Lister I can see that I'm actually getting a few different
errors happening on my system.
So, let's look at another way to refine that trigger. One fun way to refine
this trigger is to draw a box and use zone trigger, and I'm going to say must not
intersect.
I can kind of tune this in a little bit and you can see now that I've isolated
the acknowledge error. If I were to change this to must intersect instead of
must not intersect,
it's gonna show me a different set of errors and I can move this over and I
can see that this last one there's a stuff error on my system, so I can look and
see what's going on around those signals and figure out what's causing these
errors to happen.
That's it for protocol decoding and season one! Thank you so much for
watching.
Next week we're going to kick off the Keysight oscilloscopes webcast series where we
take some live webcast we've done over the past few months and we're going to
present them here on YouTube. Also, season two of the 2-minute group is going to
kick off in the fall.
Having this break in the summer is going to allow me to make sure that season 2
is just as good as season 1. I'm also going to go kayak the Grand Canyon!
If you want to know when season 2 begins, subscribe to the Keysight
oscilloscopes YouTube channel.
We also have some fun stuff cooking for later this year.
Like our Facebook page so you can hear about those when we announce it and
we're gonna have new blog post every week with more scope tips from me
Kenny, Mike- the whole scopes team, so the link for that is below.
Check out the blog.
Thank you so much for watching. I will see you later!