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How it all began: The Modular64 (Article)

It must have been 1979/80 when Atari's VCS dominated the market and Frogger, Pac-Man, Laser Blast, Keystone Kapers, Atlantis, Berzerk and Moon Patrol captivated me. I was a regular customer at Ringfoto Fehse and Hertie after school, and got up early on Saturday to be one of the first at the entrance gates, ready to get a free seat at the state-of-the art consoles Atari VCS, VideoPac Philips G7000 and so on. 

A little later, the first home computers announced themselves. VIC-20 and ZX-81, but it was the ZX Spectrum and the C64 that captivated me. After school, I made more and more trips to the Hertie department stores, even though I had already looked at everything 100 times and knew the brochures by heart 

Then, in 1983, it was Christmas. Today I reject Christmas (for logically sensible reasons), but back then it was my vehicle into the world of technology. Out of consideration for my parents, I only wanted a ZX Spectrum with 48K, which was already expensive enough. But things turned out differently. Unimaginable for me, but I got the C64 with datasette. The surprise was great. The joy was very, very big. 

From then on, my parents only saw me sporadically. I programmed numerous games, first in Basic, then in Assembler, made music and had fun. In 1987, the fun with the C64 was over because the Amiga 500 beckoned. Then I mainly made music with it. Games were interesting, but I'm more of a creative spirit, so I always tried to create something. Only playing games, was too boring for me in the long run. 

Then came many intermediate stations... Training as an electronics engineer, time as a musician with countless synthesizers, computer science studies, music and video productions, 3D animations, film documentaries, music competitions, self-employment, projects, projects, projects, ... where I built my base for what was to come. 

Then it was time, the year 2019.  These are really the original components of 2019 that I had already laid out for myself, but never built it 

If I remember correctly, it was late summer 2019 when I ordered the above components to then build an 8-bit calculator on a breadboard with a 6502 from Mexico and some auxiliary chips. It never came to that. Not in that form, anyway. 

It must have been early September 2019 when I bent over the components I had ordered, put the breadboard to rights and the other components aside, heated up the soldering iron, took it in my hand to solder the first connecting tracks. Then, just before the soldering iron touched the breadboard, I stopped the movement. I suddenly realised how many more tracks I would have had to make. 

I put the soldering iron back into the holder and thought about it for a moment. Then it suddenly became clear to me that this was not what I wanted to do. What now? Not build the board? No, I was too curious and too ambitious for that  There had to be another solution. Suddenly I remembered how I had once read something on the internet about making circuit boards. So I did some research and found what I was looking for. 

But instead of just drawing the planned breadboard and then having it made, I had the crazy idea of making a new C64. Well, as already mentioned, my ambition is sometimes great 

So why not build the smallest C64 in the world? The default size was then 100x100mm  I quickly realised that this would only work in a modular construction. Since I was mainly working in the software business at the time, I didn't know about the RC2014 project with the single-row slot cards. So if you think that my project is based on the RC2014, you are wrong. 

Anyway, this was a very ambitious project, because I didn't know anything about the inner workings of the C64. Not even how the reset line works. But that doesn't deter me, because what I don't know, I learn by doing. No hurdle is too high for me. In October 2019, I then had the first prototype, and nothing worked after 3 days , and numerous error corrections, flying lines and adapters, I got a picture for the first time. A nice moment, which I'm sure everyone who has ever built a PCB can relate to. 


I needed another 3-4 board versions until everything finally worked. After that, there were only a few more versions for fine-tuning/optimisation. In the end, this is what was on the table:

 The "Modular64" 

The difficulty with the Modular64 was the limited size and the limited number of pins available to me in each slot. There were only 72 of them. That sounds like a lot at first, but these 72 pins were not enough in the end. Not even after several attempts to change them. 

It would have been easier to allow only one specific card in each slot, then there would have been plenty of free pins, but this would also have meant the loss of free pluggability. And I didn't want that. So I had to find a solution. In the end, I decided to offer the restore button line optionally via a plug-in connection. That was the only way to solve the problem. 

All in all, I'm very happy with the result, especially because I didn't expect how stable the Modular64 works. Even when the cards are shaken, the system continues to run without a hitch

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