retrocomputer

100 Articles

Another Kind Of “Bare Metal”: 6502 Computer Powers RPN Calculator

November 17, 2020 by 11 Comments

[Mitsuru Yamada] states that one of the goals for this 6502 computer build was to make it strong enough to survive real-world usage. In that regard alone we’d call this a success; the die-cast aluminum enclosures used are a little blast from the past and lend a nice retro industrial look to the project. The main chassis of the computer fairly bristles with LEDs and chunky toggle switches for setting the data and address busses. The interior is no less tidy, with the 6502 microprocessor — date code from 1995 — and associated support chips neatly arranged on perf board. The construction method is wire wrapping, in keeping with the old-school look and feel. Even the hand-drawn schematic is a work of art — shades of [Forrest Mims].

As for programming, this machine is as low-level as it gets. Nothing but 6502 machine language here, entered manually with the toggle switches, or via an externally programmed ROM. The machine can only address 1k of memory, a limit which the code to support the RPN calculator add-on [Yamada] also built brushes up against, at 992 bytes. The calculator keypad has a 20-key matrix pad and an eight-digit dot-matrix LED display, and can do the four basic operations on fixed-point binary-coded decimal inputs. The brief video below shows the calculator in action.

We love the look of this build and we’re eager to see more like it. We’ve seen a ton of 6502 builds from discrete chips lately, and while we love those too, it’s nice to see one of the big old DIPs put back in action for a change.

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Retro Computer Trainer Gets A Raspberry Pi Refit

October 12, 2020 by 11 Comments

We know what you’re thinking: this is yet another one of those “Gut the retro gear for its cool old case and then fill it up with IoT junk” projects. Well, rest assured that extending and enhancing this 1970s computer trainer is very much an exercise in respecting the original design, and while there’s a Pi inside,  it doesn’t come close to spoiling the retro goodness.

Like many of a similar vintage as [Scott M. Baker], the Heathkit catalog was perhaps only leafed through marginally less than the annual Radio Shack catalog. One particularly desirable Heathkit item was the ET-3400 microcomputer learning system, which was basically a 6800-based computer surrounded by a breadboarding area for experimentation. [Scott] got a hold of one of these, but without the optional expansion accessory that would allow it to do interesting things such as running BASIC or even supporting a serial port. So [Scott] decided to roll his own expansion board.

The expansion card that [Scott] designed is not strictly a faithful reproduction, at least in terms of the original BOM. He turned to more modern — and more readily available — components, but still managed to provide the serial port, cassette interface, and RAM/ROM expansion of the original unit. The Raspberry Pi is an optional add-on, which just allows him to connect wirelessly if he wants. The card fits into a 3D-printed case that sits below the ET-3400 and maintains the original trainer’s look and feel. The longish video below shows the build and gives a tour of the ET-3400, both before and after the mods.

It looks as though trainers like these and other artifacts from the early days of the PC revolution are getting quite collectible. Makes us wish we hadn’t thrown some things out.

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TV Output From Arduino — 1980s Style!

September 11, 2020 by 20 Comments

We’ll admit it, we’re all spoiled. A few bucks can now buy a computer that would have been the envy of everyone back in the late 1970s or early 1980s. So it’s no surprise that [krallja] was able to use an old-style video output chip to drive a TV with an Arduino. The TMS9918A is a venerable output device, and if the old computers could drive it then it makes sense that a modern computer could too. You can see a video of the whole experiment, below.

The Internet has also spoiled us, in that it’s dead simple to find datasheets for nearly anything, even these old chips. The only real problem with such aged silicon is that they typically expect a processor with a data and address bus, but most microcontrollers now keep all of that internal. But with enough fast I/O you can simulate a bus just fine. For now, the experiment just cycles through the color output.

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A Z80 Board With Very Few Parts

July 17, 2020 by 25 Comments

The Z80 is one of those old CPUs that is both obtainable and easy to work with — at least in some versions. [Doctor Volt] put together what may be the simplest possible setups to get a working Z80 system. He has the processor, of course. But everything else — clock, memory, and power — are from an Arduino Mega 2560. You could argue that’s two chips, but the board actually has several chips on it. On the other hand, you could probably pull off the same stunt with a bare ATMega 2560.

We’ve seen this done before, but usually with a few more support chips. If you are a purist, [Doctor Volt] also has some Z80 and CP/M experiments where the Arduino only acts as a disk drive for the computer and there are only two support chips. There are three videos for both projects that you can see below.

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Gigatron Hack Chat

June 22, 2020 by 6 Comments

Join us on Wednesday, June 24 at noon Pacific for the Gigatron Hack Chat with Walter Belgers!

There was a time when if you wanted a computer, you had to build it. And not by ordering parts from Amazon and plugging everything together in a case — you had to buy chips, solder or wire-wrap everything, and tinker endlessly. The process was slow, painful, and expensive, but in the end, you had a completely unique machine that you knew inside out because you put every bit of it together.

In some ways, it’s good that those days are gone. Being able to throw a cheap, standardized commodity PC at a problem is incredibly powerful, but that machine will have all the charm of a rubber doorstop and no soul at all. Luckily for those looking to get back a little of the early days of the computer revolution or those that missed them entirely, there are alternatives like the Gigatron. Billed as a “minimalistic retro computer,” the Gigatron is a kit that takes the builder back even further in time than the early computer revolution since it lacks a microprocessor. All the logic of the 8-bit computer is built up from discrete 7400-series TTL chips.

The Gigatron is the brainchild of Marcel van Kervinck and Walter Belgers. Tragically, Marcel recently passed away, but Walter is carrying the Gigatron torch forward and leading a thriving community of TTL-computer aficionados as they extend and enhance what their little home-built machines can do. Walter will stop by the Hack Chat to talk all things Gigatron, and answer your questions about how this improbably popular machine came to be.

join-hack-chatOur Hack Chats are live community events in the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, June 24 at 12:00 PM Pacific time. If time zones have you down, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.
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An 8085 Retrocomputer From The Heart

March 7, 2020 by 22 Comments

The world of 8-bit retrocomputing splits easily into tribes classified by their choice of processor. There are 6809 enthusiasts, 6502 diehards, and Z80 lovers, each sharing a bond to their particular platform that often threads back through time to whatever was the first microcomputer they worked with. Here it’s the Z80 as found in the Sinclair ZX81, but for you it might be the 6502 from an Apple ][. For [Craig Andrews] it’s the 8085, and after many years away from the processor he’s finally been able to return to it and recreate his first ever design using it. The SBC-85 is not wire-wrapped as the original was, instead he’s well on the way to creating an entire ecosystem based around an edge-connector backplane.

The CPU board is an entire computer in its own right as can be seen in the video below the break, and pairs the 8085 with 8k of RAM, a couple of 2732 4k EPROMs, and an 8155 interface chip. This last component is especially versatile, providing an address latch, timer, I/O ports, and even an extra 256 bytes of RAM. Finally there is some glue logic and a MAX232 level shifter for a serial port, with no UART needed since the 8085 has one built-in. The minimal computer capable with this board can thus be slimmed down significantly, something that competing processors of the mid 1970s often struggled with.

Craig’s web site is shaping up to be a fascinating resource for 8085 enthusiasts, and so far the system sports that backplane and a bus monitor card. We don’t see much of the 8085 here at Hackaday, perhaps because it wasn’t the driver for any of the popular 8-bit home computers. But it’s an architecture that many readers will find familiar due to its 8080 heritage, and could certainly be found in many control applications before the widespread adoption of dedicated microcontrollers. It would be interesting to see where Craig takes this next, with more cards, and perhaps making a rival to the RC2014 over in Z80 country.

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A Z80 Computer At The Next Level

February 23, 2020 by 40 Comments

At the close of the 8-bit home computer era there were some machines produced that attempted to bridge the gap between the 8- and 16-bit worlds, either by providing a 16-bit device with a backwards compatibility mode, or an 8-bit one with enhanced capabilities to compete with its newer rivals. These products largely fell by the wayside in the face of new 16-bit only platforms, but they and the various enhanced versions of 8-bit processors that appeared over subsequent decades present a fascinating glimpse of what might have been. It’s a theme [Konstantin Dimitrov] explores with his Z20X computer project, a machine using the Zilog eZ80 processor running at 20 MHz, with 512 kB of external memory, and an interface for a 7″ TFT screen module.

The eZ80 is a more recent development, a pipelined processor capable of much higher clock speeds and addressing up to 16 MB of memory while maintaining software compatibility with the Z80. Had it come to market in the late 1980s it would have been a sensation, but instead it has appeared in embedded computers and perhaps of most interest to Hackaday readers, in TI’s line of programmable calculators.

The Z20X is designed to be a through-hole board, with the only SMD component the eZ80 itself. We can understand the motivation behind this, but at the same time wonder whether its likely builders in 2020 will be people unfazed by SMD assembly. It has a system of processor modules in case of future upgrades, and an expansion backplane with an option of an RC2014-compatible bus. There are also PS/2 keyboard and mouse connectors, a serial bus, and an on-board sound chip. The website is short on details of any software, but we’d expect it to work with the typical Z80 retrocomputer offerings such as a BASIC interpreter and the CP/M operating system.

This machine is likely to appeal to retrocomputing enthusiasts, but had it appeared even without the display in a previous decade it would no doubt have become an object of desire. It does however serve as a reminder that the Z80 line has been updated, and though most of us will have moved on it still offers a few chips that could be of interest. Meanwhile for a comparison, take a look at last year’s review of the latest in the range of RC2014 retrocomputer boards.

Thanks [yNos] for the tip.