commodore 64

126 Articles

Crossing Commodore Signal Cables On Purpose

April 29, 2025 by 18 Comments

On a Commodore 64, the computer is normally connected to a monitor with one composite video cable and to an audio device with a second, identical (although uniquely colored) cable. The signals passed through these cables are analog, each generated by a dedicated chip on the computer. Many C64 users may have accidentally swapped these cables when first setting up their machines, but [Matthias] wondered if this could be done purposefully — generating video with the audio hardware and vice versa.

Getting an audio signal from the video hardware on the Commodore is simple enough. The chips here operate at well over the needed frequency for even the best audio equipment, so it’s a relatively straightforward matter of generating an appropriate output wave. The audio hardware, on the other hand, is much less performative by comparison. The only component here capable of generating a fast enough signal to be understood by display hardware of the time is actually the volume register, although due to a filter on the chip the output is always going to be a bit blurred. But this setup is good enough to generate large text and some other features as well.

There are a few other constraints here as well, namely that loading the demos that [Matthias] has written takes so long that the audio can’t be paused while this happens and has to be bit-banged the entire time. It’s an in-depth project that shows mastery of the retro hardware, and for some other C64 demos take a look at this one which is written in just 256 bytes.

Continue reading “Crossing Commodore Signal Cables On Purpose” →

Adding An Atari Joystick Port To TheC64 USB Joystick

April 24, 2025 by 1 Comment

“TheC64” is a popular recreation of the best selling computer of all time, the original Commodore 64. [10p6] enjoys hacking on this platform, and recently whipped up a new mod — adding a 9-pin Atari joystick connector for convenience.

When it comes to TheC64 units, they ship with joysticks that look retro, but aren’t. These joysticks actually communicate with the hardware over USB. [10p6]’s hack was to add an additional 9-pin Atari joystick connector into the joystick itself. It’s a popular mod amongst owners of TheC64 and the C64 Mini. All one needs to do is hook up a 9-pin connector to the right points on the joystick’s PCB. Then, it effectively acts as a pass-through adapter for hooking up other joysticks to the system.

While this hack could have been achieved by simply chopping away at the plastic housing of the original joystick, [10p6] went a tidier route. Instead, the joystick was granted a new 3D printed base that had a perfect mounting spot for the 9-pin connector. Clean!

We’ve seen some great hacks from [10p6] lately, like the neat reimagined “C64C” build that actually appears in this project video, too.

Continue reading “Adding An Atari Joystick Port To TheC64 USB Joystick” →

C64 Assembly In Parts

April 23, 2025 by 19 Comments

[Michal Sapka] wanted to learn a new skill, so he decided on the Commodore 64 assembly language. We didn’t say he wanted to learn a new skill that might land him a job. But we get it and even applaud it. Especially since he’s written a multi-part post about what he’s doing and how you can do it, too. So far, there are four parts, and we’d bet there are more to come.

The series starts with the obligatory “hello world,” as well as some basic setup steps. By part 2, you are learning about registers and numbers. Part 3 covers some instructions, and by part 4, he finds that there are even more registers to contend with.

Continue reading “C64 Assembly In Parts” →

A Scratch-Built Commodore 64, Turing Style

April 23, 2025 by 18 Comments

Building a Commodore 64 is among the easier projects for retrocomputing fans to tackle. That’s because the C64’s core chipset does most of the heavy lifting; source those and you’re probably 80% of the way there. But what if you can’t find those chips, or if you want more of a challenge than plugging and chugging? Are you out of luck?

Hardly. The video below from [DrMattRegan] is the first in a series on his scratch-built C64 that doesn’t use the core chipset, and it looks pretty promising. This video concentrates on building a replacement for the 6502 microprocessor — actually the 6510, but close enough — using just a couple of EPROMs, some SRAM chips, and a few standard logic chips to glue everything together. He uses the EPROMs as a “rulebook” that contains the code to emulate the 6502 — derived from his earlier Turing 6502 project — and the SRAM chips as a “notebook” for scratch memory and registers to make a Turing-complete random access machine.

[DrMatt] has made good progress so far, with the core 6502 CPU built on a PCB and able to run the Apple II version of Pac-Man as a benchmark. We’re looking forward to the rest of this series, but in the meantime, a look back at his VIC-less VIC-20 project might be informative.

Continue reading “A Scratch-Built Commodore 64, Turing Style” →

Converting The C64 Mini Into A C64C

April 14, 2025 by 14 Comments

The C64 Mini is a beautiful and functional replica of the most popular computer ever made, except at 50% size and without a working keyboard. For maximum nostalgia, it was modeled after the brown breadbox C64 case which so characterized the model. However, [10p6] wanted to build a tiny C64C instead, so set about making a conversion happen.

The build is primarily about the case design. [10p6] created a nice 50% scale duplicate of the C64C, with an eye to making it work with the internals of the popular C64 Mini. The case was paired with a custom PETSCII keyboard PCB and keycaps designed by [Bleugh]. This was a key element, since it wouldn’t really feel like a functional C64C without a functional keyboard. The build also scored a bonus USB hub for more flexibility. For the best possible finish, the case, power button, and keycaps were all printed using a resin printer, which provides a more “production-like” result than FDM printers are capable of.

It’s funny how retro computers remain popular to this day, particularly amongst the hacker set. In contrast, we don’t see a whole lot of people trying to replicate Pentium II machines from the mid-1990s. If you do happen to have a crack at it, though, the tipsline is always open. Video after the break.

Continue reading “Converting The C64 Mini Into A C64C” →

Probably The Most Esoteric Commodore 64 Magazine

February 17, 2025 by 10 Comments

The world of computer enthusiasts has over time generated many subcultures and fandoms, each of which has in turn spawned its own media. [Intric8] has shared the tale of his falling down a rabbit hole as he traced one of them, a particularly esoteric disk magazine for the Commodore 64. The disks are bright yellow, and come with intricate home-made jackets and labels. Sticking them into a 1541 drive does nothing, because these aren’t standard fare, instead they require GEOS and a particularly upgraded machine. They appear at times in Commodore swap meets, and since they formed a periodical there are several years’ worth to collect that extend into the 2000s, long after the heyday of the 64.

Picking up nuggets of information over time, he traces them to Oregon, and the Astoria Commodore User Group, and to [Lord Ronin], otherwise known as David Mohr. Sadly the magazine ended with his death in 2009, but until then he produced an esoteric selection of stories, adventure games, and other software for surely one of the most exclusive computer clubs in existence. It’s a fascinating look into computer culture from before the Internet, even though by 2009 the Internet had well and truly eclipsed it, when disks like these were treasured for the information they contained. So if you find any of these yellow Penny Farthing disks, make sure that they or at least their contents are preserved.

Surprisingly, this isn’t the only odd format disk magazine we’ve seen.

A Quarter And A Dime Will Get You A Commodore 64 Softmodem

January 20, 2025 by 43 Comments

Back in the 1980s, a viable modem cost hundreds of dollars. Even in the 1990s, you were looking at spending a a Benjamin or two to get computer squawking down the phone lines. According to [Cameron Kaiser], though, it’s possible to whip up a softmodem using a Commodore 64 for much cheaper than that. How much? Just 35 cents, we’re told!

The inspiration was simple—Rockwell apparently used to build modems using the 6502. The Commodore 64 has a 6502 inside, pretty much, so surely it could be a softmodem, right? Indeed, one [John Iannetta] had done this in a one-way form in the 1980s, using the Commodore 64’s SID audio chip to output data in sound form. In 1998, he espoused the 35-cent modem—basically, the price of buying an RCA jack to hook up a phone line to your Commodore 64.

As [Cameron] found out, the concept still works today, as does [John’s] code, but it’s more like 68 cents in 2025 dollars. With the right bits and pieces, and a little code, you can have your C64 modulating data into sound at rates of 300 baud.

It’s hacky, slow, and there’s no real way to receive—the C64 just doesn’t have the chops to demodulate these kinds of signals on its own. You also shouldn’t use it on a real phone line if you don’t want to damage your C64. Still, it’s a wonderful bit of hackery, and it’s fun to see how well it works. We’ve seen some other great Commodore 64 modem projects before, like the ever-useful RetroModem. Meanwhile, if you’ve got your own communication hacks for the computers of yesteryear, don’t hesitate to let us know!