6502

159 Articles

2025 Component Abuse Challenge: The VIA Makes Noise, Again

November 14, 2025 by 3 Comments

In the days of 8-bit home computing, the more fancy machines had sound chips containing complete synthesizers, while budget machines made do with simple output ports connected to a speaker — if they had anything at all. [Normal User] appears to be chasing the later route, making PCM sound by abusing the serial port on a 6522 VIA chip.

A serial port is when you think about it, a special case of a one-bit output port. It’s designed for byte data communication but it can also carry a PCM data stream. We’ve seen this used with microcontrollers and peripherals such as the I2S port plenty of times here at Hackaday, to produce such things as NTSC video. The 1970s-spec equivalent might not be as fast as its modern equivalent, but it’s capable of delivering audio at some level. The machine in question is a Ben Eater breadboard 6502 with a World’s Worst Video Card, and as you can hear in the video below the break, it’s not doing a bad job for the era,

If you think this hack sounds a little familiar then in a sense you’re right, because Ben Eater himself made noises with a 6522. However it differs from that in that he used the on-board timers instead. After all, the “V” in “VIA” stands for “versatile”.

Continue reading “2025 Component Abuse Challenge: The VIA Makes Noise, Again” →

Photo of breadboards and bench oscilloscope

Programming The 6581 Sound Interface Device (SID) With The 6502

November 10, 2025 by 6 Comments

Over on YouTube, [Ben Eater] pursues that classic 8-bit sound. In this video, [Ben] integrates the MOS Technology 6581 Sound Interface Device (SID) with his homegrown 6502. The 6581 SID was famously used in the Commodore line of computers, perhaps most notably in the Commodore 64.

The 6581 SID supports three independent voices, each consisting of a tone oscillator/waveform generator, an envelope generator, and an amplitude modulator. These voices are combined into an output filter along with a volume control. [Ben] goes into detail concerning how to configure each of these voices using the available facilities on the available pins, referencing the datasheet for the details.

[Ben]’s video finishes with an 8-bit hit from all the way back in October 1985: Monty on the Run by Rob Hubbard. We first heard about [Ben’s] musical explorations back in June. If you missed it, be sure to check it out. It seems hard to imagine that demand for these chips has been strong for decades and shows little sign of subsiding.

Continue reading “Programming The 6581 Sound Interface Device (SID) With The 6502” →

Optimizing A QuickTake Image Decoder For The Apple II’s 6502

October 5, 2025 by 7 Comments

The idea of using the Apple II home computer for digital photography purposes may seem somewhat daft considering that this is not a purpose that they were ever designed for, yet this is the goal that [Colin Leroy-Mira] had, requiring some image decoder optimizations. That said, it’s less crazy than one might assume at first glance, considering that the Apple II was manufactured until 1993, while the Apple QuickTake digital cameras that [Colin] wanted to use for his nefarious purposes saw their first release in 1994.

These QuickTake cameras feature an astounding image resolution of up to 640×480, using 24-bit color. Using the official QuickTake software for Apple Macintosh System 7 through 9 the photographs in proprietary QTK format could be fetched for display and processing. Doing the same on an Apple II would obviously require a bit more work, not to mention adapting of the image to the limitations of the 8-bit Apple II compared to the Motorola 68K and PowerPC-based Macs that the QuickTake was designed to be used with.

Targeting the typical ~1 MHz 6502 CPU in an Apple II, the dcraw QTK decoder formed the basis for an initial decoder. Many memory and buffer optimizations later, an early conversion to monochrome and various other tweaks later – including a conversion to 6502 ASM for speed reasons – the decoder as it stands today manages to decode and render a QTK image in about a minute, compared to well over an hour previously.

Considering how anemic the Apple II is compared to even a budget Macintosh Classic II system, it’s amazing that displaying bitmap images works at all, though [Colin] reckons that more optimizations are possible.

6502 Puts On An SDR Hat

September 11, 2025 by 11 Comments

The legendary 6502 microprocessor recently turned 50 years old, and to celebrate this venerable chip which brought affordable computing and video gaming to the masses [AndersBNielsen] decided to put one to work doing something well outside its comfort zone. Called the PhaseLoom, this project uses a few other components to bring the world of software-defined radio (SDR) to this antique platform.

The PhaseLoom is built around an Si5351 clock generator chip, which is configurable over I2C. This chip is what creates the phase-locked loop (PLL) for the radio. The rest of the components, including antenna connectors and various filters, are in an Arduino-compatible form factor that let it work as a shield or hat for the 65uino platform, an Arduino-form-factor 6502 board. The current version [Anders] has been working on is dialed in to the 40-meter ham band, with some buttons on the PCB that allow the user to tune around within that band. He reports that it’s a little bit rough around the edges and somewhat noisy, but the fact that the 6502 is working as an SDR at all is impressive on its own.

For those looking to build their own, all of the schematics and code are available on the project’s GitHub page. [Anders] has some future improvements in the pipe for this project as well, noting that with slightly better filters and improved software even more SDR goodness can be squeezed out of this microprocessor. If you’re looking to experiment with SDR using something a little bit more modern, though, this 10-band multi-mode SDR based on the Teensy microcontroller gets a lot done without breaking the bank.

 

 

Microsoft BASIC For 6502 Is Now Open Source

September 4, 2025 by 29 Comments

An overriding memory for those who used 8-bit machines back in the day was of using BASIC to program them. Without a disk-based operating system as we would know it today, these systems invariably booted into a BASIC interpreter. In the 1970s the foremost supplier of BASIC interpreters was Microsoft, whose BASIC could be found in Commodore and Apple products among many others. Now we can all legally join in the fun, because the software giant has made version 1.1 of Microsoft BASIC for the 6502 open source under an MIT licence.

This version comes from mid-1978, and supports the Commodore PET as well as the KIM-1 and early Apple models. It won’t be the same as the extended versions found in later home computers such as the Commodore 64, but it still provides plenty of opportunities for retrocomputer enthusiasts to experiment. It’s also not entirely new to the community, because it’s a version that has been doing the rounds unofficially for a long time, but now with any licensing worries cleared up. A neat touch can be found in the GitHub repository, with the dates on the files being 48 years ago.

We look forward to seeing what the community does with this new opportunity, and given that the 50-year-old 6502 is very much still with us we expect some real-hardware projects. Meanwhile this isn’t the first time Microsoft has surprised us with an old product.

Header image: Michael Holley, Public domain.

The 32 Bit 6502 You Never Had

August 24, 2025 by 43 Comments

In the beginning was the MOS6502, an 8-bit microprocessor that found its way into many famous machines. Some of you will know that a CMOS 6502 was created by the Western Design Center, and in turn, WDC produced the 65C816, a 16-bit version that was used in the Apple IIgs as well as the Super Nintendo. It was news to us that they had a 32-bit version in their sights, but after producing a datasheet, they never brought it to market. Last October, [Mike Kohn] produced a Verilog version of this W65C832 processor, so it can be experienced via an FPGA.

The description dives into the differences between the 32, 16, and 8-bit variants of the 6502, and we can see some of the same hurdles that must have faced designers of other chips in that era as they moved their architectures with the times while maintaining backwards compatibility. From our (admittedly basic) understanding it appears to retain that 6502 simplicity in the way that Intel architectures did not, so it’s tempting to imagine what future might have happened had this chip made it to market. We’re guessing that you would still be reading through an Intel or ARM, but perhaps we might have seen a different path taken by 1990s game consoles.

If you’d like to dive deeper into 6502 history, the chip recently turned 50.

Thanks [Liam Proven] for the tip.

Happy Birthday 6502

August 4, 2025 by 122 Comments

The MOS Technology 6502 is a microprocessor which casts a long shadow over the world of computing. Many of you will know it as the beating heart of so many famous 8-bit machines from the likes of Commodore, Apple, Acorn, and more, and it has retained enough success for a version to remain in production today. It’s still a surprise though, to note that this part is now fifty years old. Though there are several contenders for its birthday, the first adverts for it were in print by July 1975, and the first customers bought their chips in September of that year. It’s thus only fitting that in August 2025, we give this processor a retrospective.

The Moment Motorola Never Really Recovered From

A double page advert for the MOS 6501 and 6502, advertising its low cost and high performance.
The advert that started it all. MOS Technology, Public domain.

The story of the 6502’s conception is a fascinating tale of how the giants of the early mocroprocessor industry set about grappling with these new machines. In the earlier half of the 1970s, Chuck Peddle worked for Motorola, whose 6800 microprocessor reached the market in 1974. The 6800 was for its time complex, expensive, and difficult to manufacture, and Peddle’s response to this was a far simpler device with a slimmed-down instruction set that his contact with customers had convinced him the market was looking for: the 6502.

There’s a tale of Motorola officially ordering him to stop working on this idea, something he would later assert as such an abandonment of the technology that he could claim the IP for himself. Accompanied by a group of his Motorola 6800 colleagues, in the summer of 1974 he jumped ship for MOS Technology to pursue the design. What first emerged was the 6501, a chip pin-compatible with the 6800, followed soon after by the 6502, with the same core, but with an on-board clock oscillator. Continue reading “Happy Birthday 6502” →