The story so far: I’d been tinkering with an MCP795W20 real-time clock (RTC) chip and having a frustrating time of it. Weird things were happening. It seemed very finicky. I’d put part of the problem down to using a breadboard (still think I’m not entirely wrong about that). It turns out, however, that the biggest problem was my own stupidity…. Read more »
So I decided that I’d like to add a real-time clock (RTC) to the Zolatron project because … why not? Should be easy, I thought. Lots of people have done it. All I need is the right chip. Maybe that’s where I made my mistake. As it turned out, for some reason, I already own three copies of the Microchip… Read more »
Okay, so I’m going to call it. This project is finished. Well, not finished exactly. No project is ever finished. You can always do more. And so it is with the Zolatron – I have ideas and plans that will keep me happily tinkering away for years. But I’ve met my main objective – which is to better understand how… Read more »
Yep, you guessed it – two of them. One of the side effects of ordering PCBs from the likes of JLCPCB is that you have to order at least five copies of each board. This doesn’t quite mean that I have enough PCBs to make five Zolatron 64s. For one thing, each of the machines above uses two of the… Read more »
I’ve said it before and I’ll say it again: I have no idea how you write an operating system. Even though I’ve sort-of written one. I’m calling it ZolOS. The Zolatron 64 6502 homebrew computer project started as idle curiosity that just got out of hand. I figured I’d be happy if I could get as far as writing ‘Hello… Read more »
Things are continuing apace with the Zolatron 64 6502 homebrew computer. In fact, progress has been so rapid that I haven’t really had much time to talk about it. So here’s a quick refresher – and details of the new memory expansion board. Serial killer The 6551 ACIA serial board is dead. Well, it’s not dead, but I’ve stopped using… Read more »
It’s always a good day when you get a package from the fab. There’s something simultaneously exciting and daunting about unwrapping a shiny new batch of PCBs. On the one hand, there are the possibilities promised by the new device. On the other, you’re wondering whether you made some kind of mistake in the design and if the thing will… Read more »
This is the 300th blog post on this site, and I thought it would be appropriate to mark the occasion with a summary of what’s happening with my Zolatron 64 6502-based homebrew computer project. You see, the thing is, I’m feel like I’m about to announce ‘mission accomplished’ for this project. And that’s not something I get to say very… Read more »
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 »
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 »
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 »
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 »
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 »
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 »
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 »