The 6809 Lives On In An FPGA

May 28, 2024 by Al Williams 38 Comments

At one point, the Motorola 6809 seemed like a great CPU. At the time it was a modern 8-bit CPU and was capable of hosting position-independent code and re-entrant code. Sure, it was pricey back in 1981 (about four times the price of a Z80), but it did boast many features. However, the price probably prevented it from being in more computers. There were a handful, including the Radio Shack Color Computer, but for the most part, the cheaper Z80 and the even cheaper 6502 ruled the roost. Thanks to the [turbo9team], however, you can now host one of these CPUs — maybe even a better version — in an FPGA using Verilog.

The CPU may be old-fashioned on the outside, but inside, it is a pipeline architecture with a standard Wishbone bus to incorporate other cores to add peripherals. The GitHub page explains that while the 6809 is technically CISC, it’s so simple that it’s possible to translate to a RISC-like architecture internally. There are also a few enhanced instructions not present on the 6809.

In addition to the source code, you’ll find a thesis and some presentations about the CPU in the repository. While the 6809 might not be the most modern choice, it has the advantage of having plenty of development tools available and is easy enough to learn. Code for the 6800 should run on it, too.

Even using through-hole parts, you can make a 6809 computer fit in a tiny space.You can also break out a breadboard.

It’s A CoCo! No, It’s An Apple II!

March 2, 2024 by Jenny List 2 Comments

Original retrocomputing hardware is now decades old and showing its age, so the chances are it’s more common in 2024 to experience a machine from the 1970s or 1980s by way of an emulator on a modern machine than it is on the real hardware. There’s another more limited emulation scene as similar 8-bit machines emulate each other, for example when the very similar Dragon 32 and Tandy CoCo have a go at each other’s software. Rarest of them all though is when one classic machine emulates another with a different architecture, but that’s exactly what’s happened with [DragonBytes], who has persuaded a Tandy CoCo to emulate an Apple II.

The two machines have significant hardware differences, but we’re guessing that the project is helped a little by the Motorola 6809 in the CoCo and the MOS 6502 in the Apple having both in a sense been different visions of a successor to the Motorola 6800. Thus their architectures while different, are not diametrically opposed. The other hardware is certainly not so similar though, with Moto’s 6847 display chip in the Tandy being far more conventional than Steve Wozniak’s clever NTSC hacks to achieve a color display for minimal cost on the Apple.

The project is written in assembler, and doesn’t by any means claim to support all Apple modes, or be cycle accurate. But it’s a hugely impressive achievement nevertheless.

The CoCo has an enthusiastic following, and has appeared here a few times in the past. We particularly like this video player.

Odd Retrocomputer Had A Graphics Coprocessor

August 4, 2023 by Al Williams 16 Comments

[Noel’s Retro Lab] scored an unusual 1980s vintage computer sold in Japan and Spain. The Seconinsa FM-7 appears to be a popular Fujitsu Japanese computer altered to fit the Spanish market. They seem to be pretty rare, at least in our part of the world. The outside appearance was very nice for the time, with a large keyboard and plenty of expansion ports. But the board has an unusual feature considering the era — dual CPUs. One 6809 executed your program, and another 6809 handled graphics output. You can see the machine in the video below.

There are two 32K ROMs, but the machine specifications claim only 48K. After dumping the ROMs, it turns out one of the ROMs has two copies of the same data. You can imagine they might not want to decode the entire address space. It could be that they needed 16K of space for other devices.

It wasn’t just the ROMs. The video RAM is pretty strange, too, as [Noel] explains. There are even some static RAMs the computer doesn’t claim. It appears these act as communication pipes between the two CPUs. In fact, it turns out that even the keyboard has its own 4-bit CPU, so the machine actually has a total of 3 CPUs!

This was a heavy-duty design for the time it was built. [Noel] wanted to fire it up, but he had to figure out the cables since the computer didn’t have any with it. Some clever repurposing of stock cables provided monochrome video output. Color display was a bit more complicated, but not impossible.

[Noel] winds the video up with some history of the companies behind the machine. The Spanish government wanted to use the FM-7 in the classroom, but the program failed to materialize. Want to see what it was like to program the thing? Here’s the Basic reference manual (in Spanish). Most of the documentation for the machine is either in Spanish or Japanese.

While this certainly is a rare computer, at least there’s a record of its existence. If you want to see what a Japanese computer looked like a few decades earlier, check out the FACOM 128B.

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The Keychain 6809

March 24, 2023 by Al Williams 16 Comments

When you think of tiny microcontroller boards, you probably think of a modern surface mount processor. Not [Andreas Jakob]. His 5×5 cm keychain computer rocks a 6809 CPU at a blistering 1 MHz or, if you prefer, a 6309 that runs at 5 MHz. The RAM — all 32K — is in a SMD package to make it fit, but the board also sports a 27C256 EPROM which means that chip and the CPU take up most of the PCB.

As you might expect, there’s not much else on the board. It doesn’t hurt, too, that the PCB is a 6-layer board. The board features a USB C port for power and data, but we didn’t see the USB interface chip on the schematic until we opened it in Easy EDA using the button that says “open in editor.” The schematic says it is sheet 1 or 1, but there are actually two additional “tabs” you can only see in the editor with the apparently missing pieces.

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Old 6809 Computer Lives Again On Breadboards

November 9, 2022 by Al Williams 36 Comments

Among old CPUs, the 6809 never got as much attention as some of its cousins. The Radio Shack CoCo used it and so did a construction article in Wireless World Magazine. Now [Dave] has reconstructed that computer on breadboards and it looks great. The files are on GitHub and there is even a series of videos about the machine. You can watch the first one below.

You can even read the original articles in the January 1981 Wireless World where the board used a 6802. The upgrade to a 6809 appears in the July 1981 issue. The magazine promised you could build the system for £100. Besides the 6809 there were only a few chips. A PROM, two RAM chips, A 6821 PIA, and a 74LS138 decoder for address selection. An MC1413 transistor array also allowed for a 7-segment display and a keypad along with a 7442 BCD decoder.

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A Portable Serial Terminal That Should Be From The 1970s

December 8, 2020 by Jenny List 38 Comments

The humble standalone serial terminal might be long gone from the collective computing experience, but in the ghostly form of a software virtual terminal and a serial converter it remains the most basic fall-back and essential tool of the computer hardware hacker. [Mitsuru Yamada] has created the product that should have been made in the serial terminal’s heyday, a standalone handheld terminal using a 6809 microprocessor and vintage HP dot matrix LEDs. In a die-cast box with full push-button keyboard it’s entirely ready to roll up to a DB-25 wall socket and log into the PDP/11 in the basement.

Using today’s parts we might achieve the same feat with a single-chip microcontroller and a small LCD or OLED panel, but with an older microcomputer there is more system-building required. The 6809 is a wise choice from the 1970s arsenal because it has some on-board RAM, thus there’s no need for a RAM chip. Thus the whole thing is achieved with only a 2716 EPROM for the software, a 6850 UART with MAX232 driver for the serial port, and a few 74 chips for glue logic, chip selects, and I/O ports to handle keyboard and display. There’s no battery in the case, but no doubt that could be easily accommodated. Also there’s not much information on the keyboard itself, but in the video below we catch a glimpse of its wiring as the box is opened.

The value in a terminal using vintage parts lies not only in because you can, but also in something that can’t easily be had with a modern microcontroller. These parts come from a time when a computer system had to be assembled as a series of peripherals round the microprocessor because it had few onboard, leading to a far more in-depth understanding of a computer system. It’s not that a 6809 is a sensible choice in 2020, more that it’s an interesting one.

By comparison, here’s a terminal using technology from today.

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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.