In the context of an undergraduate course on microprocessors and architecture, I'm looking at how to introduce a VGA display peripheral. This is with the specific goal that they implement the peripheral in verilog on an FPGA (they're given a microprocessor and the rest of the system).

It's VGA because of the current hardware used for the supporting labs - and I kind of like the example peripheral because it has a useful set of physical layer constraints. An LCD interface might seem like a more relevant, but then we're looking at a SPI peripheral or similar, and that defeats the object of the module.

The VGA physical layer is clearly an evolution of analogue TV and CRT technology, so it's quite tempting to start the description of how pixels need to map onto the screen by talking about the CRT and how an electron beam scans across the phosphor, line by line.

My question: how relevant is this analogy going to be to current school leavers, and will it work as a starting point for describing horizontal and vertical sync?

I've thought of trying to update the module by describing how an LCD panel would de-serialise the VGA signal, or switch to another output interface altogether, but it seems that the example I have at the moment might be worth keeping alive for a few years longer.

  • $\begingroup$ Re, "it's quite tempting to [...talk] about the CRT and how an electron beam scans..." It's not like you need to explain how a CRT works. All they need to know is that it scans the screen, line by line at a fixed rate, that the sync pulses define the top of the screen and the start of each line, and that the voltage level controls the brightness of the flying spot. Shouldn't take more than two or three minutes (assuming you show some illustrations including the wave form at different levels of detail.) $\endgroup$ Commented Sep 12, 2017 at 17:47
  • $\begingroup$ @jameslarge - Agreed - there is not a lot of wasted time, but is it too much irrelevant old context? $\endgroup$ Commented Sep 12, 2017 at 17:57

2 Answers 2


I haven't taught about analog television but thanks to my gaming related experience (both as a gamer and game development trainer) I know that the topic of horizontal and vertical sync is very important for understanding one of the more core things of computer science, the display. Further, I am all about the cutting edge stuff.

Yet, when it comes to getting the concepts of display, I am all for going to the roots, and CRT is by far the easiest way to explain these things. So, to answer your question, yes, the analogy is still relevant. And going further, It will and continue to be the starting point for studying this display stuff.

Eventually, you will have to upgrade to modern screen but CRT is definitely the go point on the table.

  • $\begingroup$ I think I am overly cautious because I read a voluminous book on TVs whilst at school, and I'm still in awe at the detail and clever circuit tricks... $\endgroup$ Commented Sep 13, 2017 at 9:02
  • $\begingroup$ technology man...old or new....always aweing and inspiring. $\endgroup$
    – Jay
    Commented Sep 13, 2017 at 11:43

Except for the latest iPad Pro and a few other specialized displays (vector, etc.), most laptop and mobile devices displays still update a 2D bitmap raster or composited texture quad at some fixed refresh rate, just like a CRT (but with much higher bandwidth these days).


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