Awakening A Dragon From Its Slumber

January 12, 2020 by Jenny List 18 Comments

For all the retrocomputing fun and games we encounter in our community, there are a few classic microcomputers that rarely receive any attention. Usually this is because they didn’t sell well and not many have survived, or were simply underwhelming machines that haven’t gathered a huge following today. One that arguably falls within both camps is the Dragon 32, a machine best known in those pre-Raspberry Pi days for being the only home computer manufactured in Wales, and for being nearly compatible with the Tandy Color Computer due to both machines’ designs coming from the same Motorola data sheet. Repeat restorer of retrocomputers, [Drygol], has given a Dragon 32 the full restoration and upgrade treatment, offering us a rare chance to take a look at this computer.

The Dragon arrived with a pile of contemporary books and software, but no power supply. A significant modification was made to the internal PSU board then to allow it to work with an Amiga unit, and the black-on-green Dragon text came up on the TV screen. Recapping and a replacement for a faulty op-amp fixed poor video quality, then it was time for a 64K memory upgrade with some neatly done bodge-wiring. Finally there’s a repair to the very period-looking analogue joystick, and a home-made interface for the more common Atari/Amiga style sticks.

The Dragon may be only a footnote in the history of 8-bit home computing, but with its good expandability and decent quality keyboard it perhaps deserved to reach more homes than it did. This appears to be the first time a Dragon has featured here, though its Tandy CoCo cousin has made it into a few stories.

Reverse Engineering An Ancient SBC With An Apple ][

August 4, 2019 by Jenny List 5 Comments

We spend a lot of time in our community discussing the many home computers from the 8-bit era, while almost completely ignoring their industrial equivalents. While today a designer of a machine is more likely than not to reach for a microcontroller, four decades ago they would have used a single-board computer which might have shared a lot of silicon with the one you used to play Pac Man.

[Epooch] recently came into possession of a CMS 9619A Advanced Single Board Microcomputer, a rather unique Programmable Logic Controller intended for industrial applications. It’s powered by a Motorola 6809 CPU and features the usual array of peripheral chips. To unlock its secrets he reached not for an array of tools from 2019 but for a venerable Apple ][e microcomputer.

In this type of 8-bit machine the various peripherals are enabled through address decoding logic that toggles their chip select line when a particular I/O address is called. Sometimes this task is performed by a set of 74 or similar logic chips, but in the case of the CMS 9619A it falls upon a Programmable Array Logic (PAL). These chips, which could be thought of as a simple precursor to today’s FPGAs, were ideal for creating custom decoding logic.

As you might expect though, a PAL is an opaque device, so to deduce the address map it was necessary to reverse engineer it using the Apple ][‘s printer card and a bit of BASIC code. It then remained to do some ROM disassembly work and wire up the serial ports, before some ROM patching with the Apple ][ as an EPROM programmer to finally access the machine’s debugger.

The 6809 is famous as the brains of Radio Shack’s CoCo and the Dragon computers, but this isn’t the first time we’ve seen it in an SBC.

Add A Host Of 8-Bit Processors To Your Arduino

April 14, 2019 by Jenny List 14 Comments

Normally when we bring you news of a retrocomputing design, it will centre around a single processor. At its heart will be a 6502, a Z80, or perhaps a 6809. There will be a host of support chips, some memory as RAM or ROM, and a bunch of interfaces. [Erturk Kocalar]’s RetroShield project for the Arduino Mega breaks all of those rules, because it supports all three of those classic processors, has no support chips, no memory, and no external interfaces beyond the shield connection to the Mega. What on earth is going on!

A closer look reveals that the project is a set of shields that use the Mega’s power to emulate all the support chips and peripherals you’d have seen on the original hardware. And while it would be impressive to have a single board with support for all three CPUs, in fact there is a PCB for each one. But that makes it no less interesting a project for those with an interest in 8-bit processors, because the focus becomes the software rather than a quest to find out-of-production silicon.

So far there is some limited demo software, and his website goes into some detail on the interfacing and code required. The Arduino can only clock the 8-bit CPU at 95kHz in software which may sound a bit low to those familiar with 1980s home computers, but it’s best to think of this as an experimentation platform and give up dreams of playing Elite. An exciting prospect comes in giving the 8-bit machine access to Arduino shields, if improbable hardware is your bag.

If this has captured your interest, you might also wish to take a look at the $4 Z80 single board computer which has a similar ethos.

New Caps And RAM Save Another Poly-1

January 17, 2017 by Jenny List 18 Comments

1980s American teenagers, if they were lucky enough to attend a school with a computer lab, would have sat down in front of Apple IIs or maybe Commodore VIC20s. Similarly, their British cousins had BBC Micros. Solid and educational machines with all sorts of wholesome software, which of course the kids absolutely preferred to run in preference to playing computer games.

New Zealanders, at least a few of them, had the Poly-1. A footnote in the 8-bit microcomputer story, this was a home-grown computer with a built-in monitor clad in a futuristic one-piece plastic shell. Non-Kiwis never had the chance to encounter its 6809 processor and 64k of RAM, the global computer business being too great a challenge for a small New Zealand technology company, especially one whose government support had evaporated.

Decades after the end of Poly-1 production, some survive in the hands of enthusiasts. [Terry Stewart] has two of them, and has posted details of how he brought life back to one that was dead on arrival. It’s a story first of a failed electrolytic capacitor and tricky-to-dismantle PSU design, then of an almost-working computer whose random crashes were eventually traced to a faulty RAM chip. It seems swapping out that quantity of DIL RAM chips is rather tedious, and of course it had to be the final chip in the final bank that exhibited the problem.

Meanwhile it’s interesting to see the design of this unusual machine. A linear power supply contrasts with the switcher you’d have found in an Apple II at the time, and the motherboard is a huge affair. it’s easy to see why this was a relatively expensive machine.

We brought you [Terry]’s first Poly-1 last year, but so far he’s the only owner whose machine we’ve seen. More mainstream 8-bit machines are a common sight here, so for something else a bit esoteric read our coverage of home computers behind the Iron Curtain, and its companion piece on peripherals behind the Iron Curtain.

[via Hacker News]

Resurrecting The Retro-futuristic Poly-1

October 11, 2016 by Nava Whiteford 11 Comments

[Tez] has acquired and resurrected a piece of New Zealand computing history, the Poly-1. To anyone who went to school in 1980s Britain, the Poly-1 appears to be a cooler, mirror universe version of Acorn’s BBC Micro. Like the humble Beeb, the Poly-1 was designed primarily for educational use. It also used a related, but superior, microprocessor (the Motorola 6809).

However while the legacy of Acorn lives on in the ARM architecture, only a few thousand Poly-1s were ever sold and it appears to have been largely forgotten.

The Poly-1’s demise was likely in part due to its high price tag — around $5,000 USD — its lack of support within New Zealand, and the difficulty that the small New Zealand company had breaking into international markets: issues which eventually killed off many similar 1980s computer companies in the UK, Japan and elsewhere.

But it’s still fascinating to look back, not just in nostalgia, but in admiration of the intrepid 1980s hackers who created these beautiful machines and the dream of a world that might have been.

Multi-target IDE For 8-Bit CPUs

November 15, 2014 by Brian Benchoff 19 Comments

A long time ago, [Martin] played with old 8-bit computers. Recently, he’s been honing his assembly skills again, and the idea of an IDE for a boatload of old systems came to him. After a year of work, he announced a multitarget IDE for 8-bit computers that works in your browser.

The project is called ASM80, and includes a code editor, a workspace to put all your code, compilers for the 8080/8085, Z80, 6502, 6800 and 6809 CPUs, emulators for all these CPUs, and emulators for a few Czech computers, the ZX Spectrum, and a few of [Grant Searle]’s single board computers.

What makes this project interesting is the syntax for all the different CPUs is pretty much the same. It’s a real, modular code editor that supports macros and everything you would expect for a code editor for ancient computers.

You can check out an assembler description here. [Martin] also has an offline, desktop-based version of ASM80 called IDE80, with a video demo of that below.

Continue reading “Multi-target IDE For 8-Bit CPUs” →

A Pick-And-Mix FPGA Retrocomputer

February 17, 2014 by Brian Benchoff 7 Comments

Cheap FPGA boards are readily available, as are VHDL implementations of classic CPUs like the 6502, 6809, and Z80. Up until now, we haven’t seen anyone take these two parts and combine them into a complete system that turns an FPGA board into a complete 8-bit retrocomputer. Thanks to [Grant]’s work, it’s now possible to do just that (server on fire, here’s a google cache) with a $30 FPGA board and a handful of parts.

In its full configuration, the Multicomp, as [Grant] calls his project, includes either a 6502, 6809, Z80, or (in the future) a 6800 CPU. Video options include either monochrome RCA, RGB VGA, or RGB via SCART. This, along an SD card interface, a PS2 keyboard, and the ability to connect an external 128kB RAM chip (64k available) means it’s a piece of cake to build a proper and complete portable retrocomputer.

What’s extremely interesting about [Grant]’s project is the fact the data and address lines are fully exposed on the FPGA board. This means it’s possible to add whatever circuit you’d like to whatever retrocomputer you can imagine; if you want a few NES gamepads, an IDE interface, or you’d like to design your own primitive video card, it’s just a matter of designing a circuit and writing some assembly.

If you’d like to build your own, search “EP2C5T144C8N” on the usual sites, grab a few resistors and connectors, and take a look at [Grant]’s documentation and upcoming examples.

Via 6502.org forums