Decoding VGA on the Digital Discovery


Recently we launched the Digital Discovery, a high speed debugging tool for embedded projects. On the resource center you’ll find tutorials telling you how to use the Logic Analyzer, but those don’t really tell you why you would use it. One such example is to decode a VGA signal. In this example, I run a script in the Script Editor, that takes the VGA data from the Logic Analyzer, and converts it into an image.

A close up of the set up.

This is just one example of the high speed applications that can be debugged with the logic analyzer and script editor working together on the Digital Discovery.

For this example, I have a simple game of Tic Tac toe (written by GitHub user Verdoss) on the Nexys 4. The user plays using the buttons and the game is displayed via VGA. Along with sending the VGA signals to the VGA port, I sent the horizontal sync, vertical sync, and all four bits of the red, green, and blue signals to two Pmod ports on the Nexys 4. Then I hooked up 14 of the Digital Discovery‘s High Speed inputs to the Pmod connectors. Since this application requires selecting 400MS/s as the sample rate, I use the High Speed Adapter and High Speed Logic probes to connect to the Pmod connectors. You can see the whole set up here:

The Digital Discovery, attached to the Nexys 4 in order to read and decode the VGA signals.

In WaveForms 2015 the Script Editor is used to run a script to control the Logic Analyzer and voltage levels through the power supplies. The script uses the Logic Analyzer to read the VGA lines from the Pmod ports, decodes them and creates an image.

You can view one window of data on the Logic Analyzer.

The Script that controls the acquisition.

This takes a few minutes. Once it’s done, you can open the image and see what was displayed on the monitor.

This is just one example of the embedded projects that can be aided by the Digital Discovery. To learn more about the Digital Discovery, check out the tutorials and getting started guide on the resource center. For more detailed instructions on this example check out the tutorial on instructables.

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When I started school I wasn’t interested in any of things I’m passionate about now. In fact originally I started out wanting to study art. But then I decided I didn’t want to have people telling me what to create, so I changed to music. Then I decided I didn’t want to ruin a hobby by making it my career. At the same time my Physics class was teaching a unit on the physics of music, and I thought that was way interesting, so I changed to physics. Then by the time physics was over I decided that the coolest part of physics was electricity and magnetism, and I may as well get a degree that transfers directly into a career. So while all this was happening, I was attending Shoreline Community College, and during that time I found my passion, or rather presented itself repeatedly, until I realized, maybe I should take a hint from the universe. While at community college, I was asked to help at the high school by tutoring chemistry students. Then I was asked to help at the elementary school by being a math Olympiad coach. I continued both because I found I really enjoyed it. I also had an opportunity, and was hired to be a tutor in the Math Learning Center at the Community College, a job I really loved. At the same time I was working as a Nanny, which I had been doing for several years, the main reason because I could and would answer the hard questions the kids asked honestly (i.e. why is the sky blue). I then was recommended by the patrons of the MLC to the transfer tutoring center (private tutoring,) and developed a wait list of students. Through all these opportunities at some point I realized that I loved watching people go from totally lost, to masters of a subject. I was also forced to admit that having all these opportunities continually renewed, I must have been somewhat good at it. So I decided I wanted to teach, which fits with my mission oriented personality. I saw a serious lack of passionate ECE professors in the institutions I attended. At WSU I continued this trend by being ask to TA for computer science and electrical engineering, being a TA for a total of 4 semesters. This continued by getting an amazing opportunity in my first semester at Washington State University to work at Digilent, an educational company. So even if I didn’t want to teach, turns out I can’t avoid it. Luckily it is my main passion.

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