Zolatron 64: Using the 6522 VIA’s timers – part 1

There’s no getting away from it. The 6522 Versatile Interface Adapter (VIA) is, well, versatile. Alongside giving you two 8-bit general purpose I/O ports – much like the GPIO pins on a Raspberry Pi, Arduino and the like – it also has a bunch of handy extra features. These include a shift register and control lines that you can employ… Read more »

Zolatron 64 – more boards, bodging and blinkenlights

Well the Zolatron 64 homebrew 6502 computer is getting spiffed up in all sorts of ways. So here’s a quick catch-up before the next big challenge. Backplane The original backplane has been working fine. But I decided to upgrade it anyway. The connectors for the boards were a little further apart than they needed to be. And the new backplane… Read more »

Elliott 405 – a simplified representation

There’s something about  this brochure that just screams 1950s. The graphics on the cover, for instance, are straight out of Mad Men. ‘A simplified representation of the National-Elliott Electronics Data Processing System’ is the kind of brochure you wouldn’t think was necessary – or appropriate – for this kind of machine. The Elliott 405 wasn’t something you bought on a… Read more »

Elliott 405 cheat sheet

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In among Big Doug’s small but treasured trove of documents relating to the GPO’s National-Elliott 405 computers is a small yet fascinating document that seems to be part cheat sheet and part marketing material. The six-page, fold-out booklet is handily sized to fit into a shirt pocket, along with your pocket protector and 6H pencil. Most of the National-Elliott 405… Read more »

Zolatron 64 ROM code – write, debug, repeat

With the basic hardware of the Zolatron 64 6502-based homebrew computer working fine, I’ve been spending most of my time on the ROM software. It turns out that writing an operating system in 6502 assembly code is harder than you might think. Well, anyway, it’s harder than I thought. But first… A quick catch-up on the state of play with… Read more »

Raspberry Pi serial and the importance of pullups

Another day, another lesson learned. My Zolatron 64 6502-based 8-bit computer uses serial for its main I/O. One day I may add video output and keyboard input. But for the time being, I’m happy to talk to it via a terminal from another machine. So far, that other machine has been my electronics workbench computer – a LattePanda Alpha. And… Read more »

Zolatron 64 – mein gott, it werkz!

Sorry about the headline. When I get excited, my German heritage sneaks out. But godammit, it’s justifed. Okay, so the first attempt at creating PCBs for the Zolatron 64 6502-based homebrew computer was not an unalloyed success. I never got as far as testing the backplane, serial board and VIA board because of a monumental screw-up on the main processor… Read more »

Elliott 405 – a fascinating glimpse into vintage computing

History isn’t just about dates and the events that get memorialised in statues. Far more fascinating is the personal and the quotidian. A thumbprint left in an ordinary ceramic bowl is a more direct connection to the lived experiences of people the past than any number of crowns and sceptres. And I think there’s an aspect of even recent history… Read more »

Dot matrix printing the easy way

Twice now I’ve declared my SmartParallel project completed, and twice it has proven to be faulty – or, at least, difficult. I’m still plugging away at it (more on that soon), but in the meantime I really wanted to be able to print out 6502 assembly code listings on my Epson MX-80 F/T III dot matrix printer. And then I… Read more »

Zolatron 64 – first PCBs

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Well, how exciting. The first versions of the PCBs for the Zolatron 64 6502-based homebrew computer have arrived, and they are very pretty. Which is just as well… I say that because at least some of these boards will serve no purpose other than as decoration. I’d made some mistakes – one annoying, one stupid but survivable, and one idiotic… Read more »

SmartParallel dot matrix printer server – redux

Well, it had to happen sometime. I finally killed a Raspberry Pi. Not on purpose, of course. I’m not a psycho. (I’ve been tested.). Nope, it was just sheer impatience and stupidity. But we’ll get to that in due course. First, let’s talk about finishing a project that was already finished. Just when you think you’re out… Sometimes you think… Read more »

Testing chips

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When a project doesn’t work, there are so many things that could be wrong. Is it the code? A loose wire? A misconfiguration of some kind? Or do you just not know what you’re doing (my favourite)? The uncertainty is exacerbated when you’re using vintage integrated circuits. Old ICs have a habit of going bad. In some cases, this is… Read more »

Zolatron 64 6502 homebrew – moving up to real hardware

You can only go so far with a breadboard. Those things are great for quick and dirty prototypes and experimentation. But there comes a point when a breadboard is an unhealthy basis for a project. And yes, I’m aware that many people have followed Ben Eater‘s lead in building 8-bit processors and 6502-based computers on breadboards. I include myself among… Read more »

Zolatron 64 6502 homebrew – processing commands

In an earlier post, I described how I was parsing commands input (via serial) into the Zolatron 64 8-bit homebrew computer in assembly language. That parsing process matched an input command with an internal list and the result was a ‘token’, a single integer value of $80 or more representing that command that is placed in a memory location. Or… Read more »

Zolatron 64 6502 homebrew – parsing inputs in assembly

Okay, so this is going to be a long one. Grab a coffee, settle down and we’ll begin… The last time we talked, I was able to send messages to the Zolatron 64 6502 homebrew computer via its serial port. But all it could do was print those messages to the LCD screen. It’s time to actually do something with… Read more »