Minimalist 6502 System Uses A CPU And Not Much Else

November 22, 2022 by Robin Kearey 19 Comments

A central processing unit, or CPU, is the heart of any computer system. But it’s definitely not the only part: you also need RAM, ROM and at least some peripherals to turn it into a complete system that can actually do something useful. Modern microcontrollers typically have some or all of these functions integrated into a single chip, but classic CPUs don’t: they were meant to be placed on motherboards along with dozens of other chips. That’s why [c0pperdragon]’s latest project, the SingleBreadboardComputer, is such an amazing design: assisting its 6502 CPU are just four companion chips.

The entire system takes up just one strip of solderless breadboard. Next to the CPU we find 32 KB of SRAM, 32 KB of flash and a clock oscillator. The fifth chip is a 74HC00 quad two-input NAND gate, which is used as a very tiny piece of glue logic to connect everything together. Two of its NAND gates are used for address decoding logic, allowing either the ROM or RAM chip to be selected depending on the state of the CPU’s A15 line as well as blocking the RAM during the low phase of the system clock. The latter function is needed because the address lines are not guaranteed to be stable during the low phase and could cause writes to random memory locations.

The remaining two NAND gates are connected as an RS-flipflop in order to implement a serial output. This is needed because the CPU cannot keep its outputs in the same state for multiple clock cycles, which is required for a serial port. Instead, [c0pperdragon] uses the MLB pin, normally used to implement multiprocessor systems, to generate two-clock pulses, and stores the state in the flipflop for as long as needed. A few well-timed software routines can then be used to transmit and receive serial data without any further hardware.

Currently, the only software for this system is a simple demonstration that sends back data received on its serial port, but if you fancy a challenge you could write programs to do pretty much anything. You could probably find some inspiration in other minimalist 6502 boards, or projects that emulate a complete motherboard in an FPGA.

The State Of The SBC Interface Ecosystem, Is It Time To Design A Standard?

October 5, 2022 by Jenny List 132 Comments

We are spoiled for choice when it comes to single board computers, whether they be based around a microcontroller or a more capable SoC capable of running an operating system such as GNU/Linux. They can be had from well-established brands such as Arduino, Adafruit, or Raspberry Pi, or from a Wild West of cheaper Far Eastern modules carrying a plethora of different architectures.

Everyone has their own favourite among them, and along with that comes an ecosystem of operating systems and software development environments. There’s another aspect to these boards which has evolved; certain among them have become de facto interface connector standards for hardware peripherals. Do these standards make any sense? Let’s talk about that.

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Front and back of a handheld 6502 computer with bubble LED displays

The Pocket265 Is A Pocket-Sized 6502 Single-Board Computer

September 7, 2022 by Robin Kearey 13 Comments

Single-board computers have been around ever since microprocessors became affordable in the 1970s and never went away. Today we have Raspberry Pis and LattePandas, while back in the ’70s and ’80s there were the Ferguson Big Board, the KIM-1 and a whole array of Intel SDK boards. Although functionally similar to their modern counterparts with a CPU, RAM, ROM and some basic peripherals, the old boards were huge compared to today’s tiny platforms and typically required a rather beefy power supply to operate.

It doesn’t have to be that way though, as [Aleksander] shows with the Pocket265: a handheld 6502 single-board computer somewhat reminiscent of the famous KIM-1. Like that classic machine, it’s got a hexadecimal keypad to enter programs using machine code and a row of LED displays to show the programs’ output. Unlike the KIM, the Pocket265 is small enough to hold in one hand and uses bubble LED displays, which make it look more like a programmable calculator from the 1970s. It comes with a lithium battery that makes it truly portable, as well as a sleek 3D printed case to make it more comfortable to hold than a bare circuit board.

The single ROM chip contains a monitor program that runs the basic user interface. It also makes programming a bit less tedious by implementing a number of system calls to handle things like user input and display output. A serial EEPROM enables local data storage, while a UART with a USB interface enables data transfer to other computers. If you’re interested in building and programming such a machine yourself, [Aleksander] helpfully provides code examples as well as full hardware documentation on his GitHub page.

The 6502 remains a firm favorite among hardware hackers: some projects we recently featured with this CPU include one beautifully made machine, this easy-to-build single-board computer and this huge breadboard-based contraption. Looking for something smaller? Try this tidy little board or this 6502 coupled to an FPGA.

A purple PCB with many DIP chips including a 6502

Hackaday Prize 2022: Reuse Those DIP Chips To Make A 1980s-Style Single-Board Computer

May 28, 2022 by Robin Kearey 30 Comments

With the Great Chip Shortage still delaying deliveries of new components, now might be a good time to look around your lab and inspect those piles of chips that you thought “might come in handy one day”. Chances are you’ll find a good stack of 74xx series logic, once ubiquitous but today mostly obsolete thanks to powerful microcontrollers and FPGAs. It would be a shame to let them go to waste, so why not use them to make a neat 1980s-style computer?

With this idea in mind, [Anders Nielsen] designed the ABN6502: a single-board computer based on the venerable 6502 processor, but with relatively modern interfaces like a VGA monitor output, a PS/2 keyboard connector and even a wireless module to simplify firmware uploads from a PC. One design requirement was to minimize the number of new components needed; the average hacker interested in building the ABN6502 will probably have many of the chips lying around somewhere in their workshop.

The component list reads like a typical bill of materials for a 6502-based computer, but comes with a lot of flexibility to allow for part subsititution. For the CPU, both the classic NMOS 6502 as well as the modern CMOS-based 65C02 are supported, along with their 6522 companion chip that provides I/O ports and timers. A ROM socket can hold either modern, fast flash chips or traditional but slow UV-erasable EPROMs.

Instead of using DRAM chips with their complicated refresh requirements, [Anders] went for 32 KB of SRAM to implement the main memory; unaffordable in the ’80s but easily available today. Standard 74xx series logic chips glue all the components together, again with several options to add or remove features as the user prefers. Pin headers bring out the I/O ports for easy connection to external peripherals.

The ABN6502’s software library is currently limited to a bootloader, but a complete development toolchain based on the CC65 compiler should make it easy to develop all kinds of programs on this platform. We’ve already featured the clever wireless ROM flashing system, as well as a demonstration of the 6502 driving RGB LEDs.

Continue reading “Hackaday Prize 2022: Reuse Those DIP Chips To Make A 1980s-Style Single-Board Computer” →

An M-Core module plugged into its devboard. Around it are Ethernet, HDMI, Type-C, two USB-A ports, one MicroSD card socket and one unpopulated footprint for a WiFi module

MangoPi To Bring A SD-Card-Sized Linux Module

April 1, 2022 by Arya Voronova 14 Comments

Today’s Diminutive Device is a small castellated System-On-Module (Twitter link, nitter proxy) from [MangoPi] called M-Core, with a quad-core A53 CPU and 1 GB of RAM. As such, it’s very capable of running Linux, and even sports an HDMI output! Taking a closer look at the devboard picture, we can spot traces for three USB 2.0 ports, what seems to be two SDIO interfaces for MicroSD or WiFi cards, and an Ethernet MagJack with its termination network. This is a decent set of interfaces, rivaling what we’d expect out of a Pi Zero!

More importantly, this module is as small as an SD card itself – or as an OLED display that we hobbyists sprinkle onto our projects. Having power of Linux in such a small footprint is certainly something to behold! The back of the module is mostly flat, save for a few decoupling capacitors on the other side of the CPU – it seems, an Allwinner H616. On top of it, we can see the CPU itself, a small buck regulator and a DDR3 RAM chip, as well as tightly-packed passives. There’s even an unpopulated footprint for a DFN8 QSPI flash chip – with a lightweight enough OS build, you could perhaps dedicate your MicroSD card to storage only.

The devboard for uses the “FlexyPins”-like connectivity technique we’ve covered recently, and [MangoPi] say they bought those pins on TaoBao. We can’t help but be a bit amused at the thought of putting HDMI through such connections, but it seems to work well enough! Castellated modules like these are relatively easy to work with, so it shouldn’t be hard to literally pop this module out of the devboard and figuratively pop it onto your PCB. Next step is, reportedly, porting Armbian to this board, likely solving quite a few software support hurdles.

MangoPi have been posting updates on their Twitter page over the last few weeks, and, as it comes with the format, a lot of questions are left unanswered. Why does the devboard only show a single linear regulator of the kind we typically expect to deliver 1 A at most? Will we get higher-RAM versions? What’s the price going to look like? Will this module ever get to market? We can only hope, but if it does indeed, we are sure to see a few projects with these, whether it’s smart glasses, smart displays, phones, handhelds or malicious wall chargers. As usual, community makes or breaks an SBC, and we shall watch this one closely.

We thank [WifiCable] and [DjBiohazard] for sharing this with us!

Another Homebrew Linux Board Success Story

January 3, 2022 by Tom Nardi 26 Comments

It’s truly incredible what the hobbyist is now capable of. While it would have seemed all but impossible a few years ago, we’re happy to report that yet another dedicated hardware hacker has managed to spin up their own custom Linux single-board computer. Creator [Ian Kilgore] tells us the only goal when developing CATFOOD (yes, that’s the name) was to gain confidence with at-home board production, so it looks like a success to us.

To those who’ve been keeping an eye on this sort of thing, it will probably come as no surprise to hear [Ian] was inspired by the work of [Jay Carlson], who arguably kicked off this whole trend when he put together a bevy of homebrew Linux boards in an effort to compare different System-in-Package ICs. His incredibly detailed write-up of the experience and lessons learned along the way has emboldened other brave souls to take up the challenge.

The USB-C powered board uses an ARM i.MX 6ULL processor and features DDR3, NAND flash, and an Ethernet interface. That last one was the biggest deviation from the reference design, which meant it took a little fiddling to get right. For anyone playing along at home, [Ian] collected up the lessons learned while developing CATFOOD, bringing the whole learning experience full circle.

If you’re interested in more homebrew Linux SBCs, we’d highly recommend reading up on the WiFiWart developed by [Walker]. Over the course of about six months, we got to watch the open hardware board go from concept to a diminutive first prototype.

Where Are All The Cheap X86 Single Board PCs?

June 17, 2021 by Jenny List 154 Comments

If we were to think of a retrocomputer, the chances are we might have something from the classic 8-bit days or maybe a game console spring to mind. It’s almost a shock to see mundane desktop PCs of the DOS and Pentium era join them, but those machines now form an important way to play DOS and Windows 95 games which are unsuited to more modern operating systems. For those who wish to play the games on appropriate hardware without a grubby beige mini-tower and a huge CRT monitor, there’s even the option to buy one of these machines new: in the form of a much more svelte Pentium-based PC104 industrial PC.

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