Category Archives: Zolatron

Zolatron 64 6502 homebrew computer – first boot

Okay, so the headline is overstating matters a little, but this thing is making progress. Here’s a quick series recap: I decided to brew my own 6502-based computer. Rather than start from nothing, I built a kit, with partial success. And I’ve been following along with Ben Eater’s 6502 project on YouTube. Both taught me a lot. However, even before… Read more »

Zolatron 64 6502 homebrew computer & Ben Eater’s project – changes to the ROM

In my previous post, I mentioned how, while I’m following along with Ben Eater’s 6502-based homebrew computer project, I’m also making some revisions of my own. One of these is to use my own address decoding scheme. So far, things are working okay, but that post included a note about how I’m going to have to make some changes to… Read more »

Following Ben Eater’s 6502 project – parts 5 & 6

Back in the first half of February, Ben Eater added parts 5 and 6 of his YouTube series on building a 6502-based homebrew computer. The enhancements he made gave the computer something it has been sorely lacking – memory. And the reason the computer needed memory was so it could have a stack. Up to that point, the code had… Read more »

Zolatron 64 6502 homebrew computer – new address mapping and decoding

Although it is possibly the slowest computer development programme in history, my Zolatron 64 6502-based homebrew design has made some progress. And this is largely due to the fine folks over at the 6502.org forum. Specifically, I have made changes to how I’m mapping the 64KB address space and the decoding I’m using to do that. I’ve been following along… Read more »

Following Ben Eater’s 6502 project – part 4

Ben Eater’s exciting 6502 project has reached the next stage – adding a display. But before I could play along, I had some remedial work to do. I’d achieved the previous stage of being able to get the LEDs to light up, but not reliably. Something was glitching and would cause the machine to go haywire. This isn’t entirely surprising… Read more »

6502 homebrew: display and keyboard problems

The Apatco 6502 breadboard computer kit I’ve been building is complete. The next stage was to make it more so. A word of warning, though. This story does not have a happy ending. Nonetheless, someone may find the attempt at debugging entertaining or instructional, so here it is. The kit is sold (or perhaps ‘was’ would be better, as it… Read more »

6502 homebrew: the software toolchain

Now that the Apatco kit is working – at least the basic version (having trouble with the keyboard and display upgrade) – it’s time to mess around with writing code for it. Many people swear by the now-abandoned CC65 as their compiler/assembler of choice for 6502 homebrew computers. But I’m going with Beebasm. Although inspired by and largely aimed at… Read more »

6502 homebrew: debugging the kit #2 [solved]

If in doubt, start again. That’s not a real saying, but it should be. As we saw in the last post, the Apatco 6502 breadboard computer was finally wired up but refusing to work. I’d fixed my faulty ROM code, buzzed out all the address and data lines to check they were connected correctly and determined that the reset circuit and… Read more »

6502 homebrew: debugging the kit #1

Okay, so it was time to deal with something that has been nagging at me for a while. I have this Apatco kit 6502 breadboard computer kit and never quite got around to finishing the basic setup. It takes a lot of wiring. I just got tired, put it in a box and shoved it in the projects cupboard. For… Read more »

Homebrew 6502: a new way to start

My Zolatron 64 homebrew 6502 computer project has stalled of late. But it is high on the list of things to restart once I get current projects out of the way. And a recent development has inspired me to look at it again. If you’ve been here before, you’ll know that my plan was to first build a kit –… Read more »

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 »