Gigatron - a homemade microcomputer without a processor

The Gigatron microcomputer is a minimalistic 8-bit retro computer built according to an unusual design: it does not have any complex logical integrated circuits, there is not even a microprocessor ! Its CPU is built on the classic logic elements of the 7400 series, also known as TTL logic chips. In fact, all the elements of a computer at once are the processor. These simple chips not only form the CPU, but also perform all the tasks that usually require additional peripherals. Despite its simple and compact design, Gigatron works as an 8-bit single-board microcomputer on which you can play video games.

Gigatron is a hobby project of Walter Belger, a hacker, information security specialist and now director of information security at Philips. This Monday, September 9, Walter arrives in our Hackspace, where he will talk about the device of Gigatron, the history of the creation of the project and show it live.

Under the cut, more about Gigatron and the announcement of a meeting with the creator in Moscow.

Bit of theory

Transistor-transistor logic is a type of digital logic circuits built on the basis of bipolar transistors and resistors. The name transistor-transistor arose due to the fact that transistors are used both to perform logical functions (for example, AND, OR), and to amplify the output signal (unlike resistor-transistor and diode-transistor logic (DTL)).

^{Simplified diagram of element 2 AND NOT}

The TTL element is based on a multi-emitter bipolar transistor. If at least one of its emitters is supplied with a voltage of 0V, the transistor will be in saturation mode and a logical zero will be present on its collector. Depending on the circuit of the input and output stages, we will get one or another logical operation of our element.

^{Old TT74 SN7400 chip released in the 70s}

In the 80s, many gaming machines, as well as some household computers, were produced on TTL chips. The most famous of these are Apple I, which Steve Wozniak worked on.

An example of such an Apple 1 computer, it is also made on TTL logic, but still has a microprocessor.

^{The Apple I computer is partially built on TTL logic but has a microprocessor}

History of creation

The author of the original concept is Marcel van Kervinck. He assembled the first Gigatron prototype on a breadboard. The whole process from development to the final project is fixed here: hackaday.io/project/20781/logs

The computer runs at a clock frequency of 6.25 MHz and performs one 8-bit operation per cycle.

^{The first version of the gigatron assembled on a breadboard}

Why such old chips?

The authors explain it this way:

Of interest, and to better understand the basic architecture of the computer. And also to fiddle with the iron that we had at that time. In December 2016, we were amused by the idea of assembling a computer on TTL chips, which would be powerful enough to play tic-tac-toe on an 8x8 LED screen. In the end, something like this should be done by every engineer at least once in a lifetime.

Why is all this necessary?

At the gigatron, one can study the fundamental principles of operation of modern computers and processors. Due to the fact that all elements of the computer are quite primitive, even a novice engineer can understand the principle of their work. It’s also just fun!

What can I run?

You can try your computer at work on the gigatron.io/emu software emulator

In standard firmware are available:

Game snake
Game racer
Tic-Tac-Toe game
Tetris game
Many Mandelbrot - fractal drawing program
Image viewer
Loader for programs
BASIC environment
WozMon - Steve Wozniak's classic memory editor and memory monitor for Apple I

UDP: Meeting video

Slides : gigatron.io/walter/gigatron-neuron.pdf

Walter Belgers is one of the creators of Gigatron, a hacker who has worked in information security his whole life, mainly as a pen tester, and is currently the director of information security at Philips. In combination, Chairman of Toool - The Open Organization of Lockpickers. Walter soldered back in the 70s, but never before had he built a real computer entirely.

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Pro Hux Space Neuron

Huxpace Neuron is a community of geeks and techno-enthusiasts in the center of Moscow. We regularly host events for people who are fond of technology and their non-standard application. The rest of the time, we always have jobs for engineers: with a soldering iron, an oscilloscope and everything you need for DIY, electronics design and construction. And here you can play consoles and tables in the creative circle of nerds.