DDL-4 Is A Visually Pleasing Modular CPU

Today’s CPUs are so advanced that they might as well be indistinguishable from magic, right? Wrong! Fundamentally, modern CPUs can be understood logically like any other technology, it’s just that they’re very fast, very small, and very complex, which makes it hard to get to grips with their inner workings. We’ve come a long way from the dawn of the home computer in the 80s, but what if there was something even simpler again, built in such a way as to be easily understandable? Enter the DDL-4-CPU, courtesy of [Dave’s Dev Lab].

The DDL-4 is a project to build a modular 4-bit CPU using bitslice methods. This is where computations are broken down into simple operations with two-bit inputs, which are executed with basic logic gates like NOR and XOR. This is great for building a CPU from individual parts, as logic chips are readily available and their operation is readily understood. That’s what’s used here – good old 74-series logic, which you can find just about anywhere!

The build consists of a series of modules, each on its own colourful PCB and labeled on the silkscreen. These modules can then be configured and plugged together with edge connectors to build the CPU. The work builds upon [Dave]’s earlier work on the Mega-One-8-One, a recreation of the 74181 Arithmetic Logic Unit for educational purposes.

If you’re learning about computing in a bare-metal sense, projects like these that create CPUs from the ground up are a great way to get to grips with the basic concepts of computation. Once you’ve tried this, you could always graduate to building a 6502 in Minecraft.

16 thoughts on “DDL-4 Is A Visually Pleasing Modular CPU

    1. Technically it’s automatically true. It’s actually that automatic copyright and it’s enforcement that makes free software and open-source-hardware’s ‘copyleft’ licenses enforceable. So maybe he just hasn’t decided on a license to give it yet.

      1. I couldn’t see any licencing comments anywhere and he firmly states “All Your ISA Belong to Me!” so I am left to assume that’s the direction it might go. Even with that ambiguiity It’s a nice project so keep up the good work.

      2. I’m in the process of creating some additional educational materials and designs that compliment the DDL4-CPU. I’d like to be able to release all of the materials together under compatible licenses. To prevent any mix-ups, I am waiting until then to announce the licensing for the DDL4-CPU. The schematics are released now, in much the same way that in the “good ol’ days” you would get a schematic in a magazine or with a kit that you purchased. It’s for reference purposes, there to inspire and educate, but not to sell…

    2. How is that different from when construction articles were published in magazines?

      You could build from the article. You could learn from it. You could modify the project. You could use what you learned in some other way. You could turn around and write your own article, of your modified version.

      You couldn’t copy the article. You probably couldn’t mass produce what was in the schematic.

      People talk about “open source hardware” but then condemn those who do produce their own version. For most people it’s just informational since the circuitry is too dense to build at home and esoteric parts may not be available in single quantity, so they have to buy the assembled unit (not unlike the magazine days, when the articles were often just ads for a kit, too many hard to get arts or too much work to assemble at home).


      1. Indeed you are correct in your assessment, however i did go to great lengths to make sure all of the components i used in the project are still available via digikey and mouser in single quantity. No obsolete parts were used in the design. Additionally, i made sure that all the components are reasonably solderable by hand…

  1. I still see 4-bit micro-controllers in microwave oven control panels.

    Unfortunately they are OTP and there is no FLASH version, otherwise I could have lots of fun!

    1. you are exactly right! this is what got me looking at creating my own. this version is greatly expanded… there might be a more concise version in the future!

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