Zolatron 64: 6502 bare metal random

There’s a problem when you build your own computer and therefore have to write your own operating system. All the things you rely on when coding in other environments – such as maths functions – are not there. You have to write them yourself. The Zolatron 64, like most homebrew computers, is effectively a bare metal project. I’m writing all… Read more »

Zolatron 64: being persistent

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In an earlier post, I described how I can now load software on to the Zolatron 64 6502 homebrew computer. The LOAD command was pretty basic – you couldn’t specify a file. Instead it just loaded the same file (zd.bin) which I’d have to overwrite if I wanted to load different code. Well, those days are over, and the Zolatron… Read more »

Casio fx-590 – reviving an old friend

It was about to go in the recycling pile when I thought, “I wonder if I can save it.” There’s no telling how old this lovely Casio fx-590 calculator is, because in spite of deploying my best Google-fu I can find very little information on it. One source suggested that maybe it came out at the beginning of the 1990s…. Read more »

Zolatron 64: More adventures in level shifting

In a previous post, I detailed how I’m having to shift voltage levels on signals running between a 65C22 VIA chip and the GPIO pins of a Raspberry Pi. The solution I settled on was to go for simple voltage dividers using pairs of resistors. And that’s been working fine. I mean, you’d expect it to work with the 5V… Read more »

Zolatron 64: The start of an operating system

Let’s be clear about this, I have no idea how you write an operating system. I just know you need to have one. When I first started writing ROM code for the Zolatron 64 (Z64) 6502-based homebrew computer all that really mattered was getting things to work. And I was amazed when they did. I was following in the footsteps… Read more »

Zolatron 64: Creating a disk drive (sorta)

As I mentioned before, the Zolatron 64 6502-based homebrew computer (Z64) needs some kind of persistent storage. And these days there is no shortage of options. If you search around the interwebz for homebrew projects you’ll discover a treasure trove of clever solutions. But many of these involve implementing some form of existing technology. For example, you can employ a… Read more »

Zolatron 64: Interfacing the 6502 with the Raspberry Pi

Pretty much every computer needs persistent storage. And these days we’re spoiled for choice – everything from hard drives down to micro SD cards being capable of holding more information than I can comfortably imagine. With clever interfaces, these options are also open to builders of homebrew computers, like the 6502-based Zolatron 64 (Z64). But it does mean grappling with… Read more »

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 »