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Triggering And Decoding Serial Protocols On An Oscilloscope - Workbench Wednesdays 34

 

Everything with a microcontroller has serial busses in it. Busses like UART, I2C, and SPI are very popular choices. When you have a problem with a sensor that uses one or the bus itself, you can use an oscilloscope or logic analyzer to “decode” the traffic. These decoders convert the 1s and 0s into readable HEX or ASCII characters.

 

Supplemental Content:

 

Bill of Material:

Product Name Manufacturer Quantity Buy Now
[Bundle] Development Kit, Analog Discovery 2 Pro Bundle, 30MHz Oscilloscope, 12MHz Waveform Generator Digilent 1 Buy Now
RTM3000 - 4 Channel Oscilloscope (RTM3K-COM4) Rohde & Schwarz 1 Buy Now
PicoScope 2204A - USB 2 Channel Oscilloscope PicoScope 1 Buy Now
Arduino Uno Arduino 1 Buy Now

 

  • in reply to neilk

    One the things I really like about the PicoScope software is how full-featured it is. When they first introduced their PicoScope 2000A series, they were the first oscilloscope manufacturer to give away serial decode. (Well, officially, anyway.)

     

    I just wish it was a little more robust in terms of searching through an acquisition's decode to find specific activity.

  • in reply to koudelad

    Are. You. Kidding. Me!

     

    I had NO idea that was there. My eyes completely missed it. All the times I used the AD2, I thought "why doesn't it do protocol?!" Wow.

     

    Thank you David. I'll have to think about to address that as a follow-up.

  • Other very popular analyzers are the one's made by Saleae . They are not cheap, but the key is the control software, which does all the graphics and display and decoding.

    By the way, their control software is so good and popular that chinese clones of their hardware can use their software.

  • James, thank you so much for that.

     

    I've owned a picoscope 2204A for some time and didn't realise it could decode buses image

     

    I've just tried it on a UART I'm working with, and successfully decoded Hello World!

     

    Thanks again

     

    Neil

  • Good episode, James.

     

    I have one correction: Analog Discovery 2 has great trigger options and they helped me to debug my I2C sensor network numerous times.

    Here is a screenshot from your video with the highlighted control area:

     

    image

     

    In addition to that, AD2 has the ability to power the sensor (if it is not so power hungry), do the I2C scan and perform various scripts. This is a huge time saver to do some first tests before debugging a micro-controller code.

     

    David

  • From YouTube:

    But why use an expensive oscilloscope rather than use a cheap 10$ logic analyzer to analyze serial protocols? Any benefits?

    As I mentioned in the video, one benefit to using an oscilloscope is that you can correlate the activity on the digital bus with an analog channel. If your digital signals are getting interference from somewhere else, a logic analyzer alone may not be enough.

     

    Another reason is that most of us already have an oscilloscope on our workbenches. No need to pull out a logic analyzer and a laptop to see what is going on.

     

    Last, remember some logic analyzers, especially low cost do not do trigger on serial busses. They can only decode.