Tag Archives: computer

6502: more fun with clocks

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Things can get a little confusing with the 6502 microprocessor’s clocks. The datasheet details three clock pins which, for the current version of the chip are PHI2, PHI2O and PHI1O. And with older versions of the 6502 you’ll see PHI1 instead of PHI2. As I detailed in a previous post, the situation is actually simpler that it first seems. It… Read more »

Zolatron 64: riding the address bus

The Zolatron 64 6502-based homebrew computer has a 16-bit address bus and I want to be able to interact with it manually. How do we do that? The answer is a front panel with switches and lights, as outlined in the last post. But it’s going to be a bit more complicated than just wiring each line of the bus… Read more »

Zolatron 64: initial thoughts on a front panel

Any self-respecting retro-style homebrew computer needs two things – switches and blinkenlights. Otherwise, why bother? I haven’t got a working computer yet but already I’m thinking about a front panel for it. This will be inspired, to some extent, by the Altair 8800 and also by the PDP-8, both of which I have in the form of modern replica kits…. Read more »

Zolatron 6502 homebrew computer – clocking in

Sometimes the things that confuse you most turn out to have the simplest solutions – and so it was with the clock for my Zolatron 6502 homebrew computer. First, let’s deal with the 6502’s clock pins. There are three of them and they’re called PHI1O, PHI2 and PHI2O – except when they’re not. Older versions of the 6502 have PHI1… Read more »

Zolatron 6502 homebrew computer – a few tweaks

Within a couple of hours of posting the schematic for the main board of my Zolatron 6502 homebrew computer the doubts had already started to set in. I made the mistake of visiting Grant Searle’s site. I’m already familiar with his work having built one of his projects (an FPGA-based CP/M computer), and so I know he’s forgotten more than… Read more »

Zolatron 6502 homebrew computer – main board

Well, things are finally happening and I actually have a schematic for the main board of the Zolatron 64 6502-based homebrew computer. I’m not saying it’s a good schematic. And I’m certainly not claiming that it will work. But it passes the Electrical Rules Check and I don’t think I’ve missed anything out. So that’s an achievement in itself. Click on… Read more »

Zolatron 64 6502 computer: the backplane dilemma

Having looked at a lot of homebrew computers online, including the popular RC2014, it seemed obvious that the best way of going about my own project is to opt for a backplane design. But maybe it’s too obvious. Just as I was ready to get started with designing the Zolatron 64 I stumbled across this page (via the excellent 6502.org… Read more »

Building a 6502 computer – a place to start

We all have to start somewhere. Almost as soon as I’d decided I would build a 6502-based micro I realised that the learning curve is steep. It’s not like embarking on a new programming language where you can write a ‘Hello world’ program and go from there. When building a computer, there are many pieces that have to come together and… Read more »

From the archives: Amstrad PPC 640 review

This piece was written for Which PC? when the Amstrad PPC first came out in 1988. I can still recall to this day how the Amstrad creaked and groaned. This was probably the cheapest-feeling computer I’ve ever encountered. And as for powering it from 10 C-size batteries – holy crap. Given the lousy battery life – you’d have to carry around… Read more »

Zolatron: logo upgraded

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Yeah, I know what you’re thinking … he really should get on with building the damn computer. But I have a thing about fonts, so sue me. I was rather pleased with the original Zolatron 64 logo. I chose a font called Eurostyle because it was the most 1970s-looking one on my machine. Then I read about the history of… Read more »

Zolatron: 6502 address decoding

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This was something I’d always wondered. When you have data on a bus, how do you ensure it’s read by the device that needs it, and only that device? And when you read data from a device into the microprocessor, how does the processor read data only from that device? What we’re about to embark on here is address decoding…. Read more »

Zolatron 64: starting point

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Having decided to build a 6502 microcomputer, I was immediately successful in overcoming the first hurdle – and possibly one of the most critical stages in the whole project – by coming up with a name for it. It’s the Zolatron – or the Zolatron 64 to be precise, because it will have a total of 64K addressable memory. However, that… Read more »

Building an 8-bit 6502 computer

So I’ve decided to build an 8-bit computer based on the 6502 microprocessor. Because nothing screams ‘success!’ like creating something that was obsolete 30 years ago. The truth is that I got into retro-computing partly because I wanted to understand computers better. Yes, I can code well enough for my needs in Python, Objective-C and Swift using sophisticated frameworks, and… Read more »