When making a birthday cake a bit more personal, one can create a novelty themed confection appropriate for the lucky recipient. In the case of [Spencer Owen], who you may know as the creator of the RC2014 retrocomputing ecosystem, it was appropriate to have one of the little machines at work somewhere, so [peahen] did just that. The result is a cake in the shape of an IMSAI 8080 microcomputer, but it does more than just look the part. This is a working replica of the classic machine, powered as you might expect by an RC2014 sitting next to it.
The lights are a set of addressable LEDs, and the switches are made from appropriately colored sweets. Sadly the plan to make these capacitive touch switched failed as the wiring became buried in the icing, but the LEDs deserve a second look. They’re encased in translucent heatshrink sleeving which is embedded under a layer of white icing, which is translucent enough, but on top for the classic panel light look are a set of edible cake-maker’s jewels. Best of all while all except the electronics is edible, the front panel is robust enough to have been removed from the cake in one and thus will live on.
We rather like the idea of electronics meeting sugarcraft, because fondant is a surprisingly versatile medium that deserves attention much further than just confectionery. We remember it being a popular cheap way to experiment with 3D printing back at the dawn of open source printers, and it still has some potential. Meanwhile if you’ve not seen the RC2014 we reviewed its original version back in 2016, and since then it’s evolved to become an ecosystem in its own right.
Earlier this year Zilog stopped production of the classic 40-pin DIP Z80 microprocessor, a move that brought a tear to the eye of retro computing enthusiasts everywhere. This chip had a huge influence on both desktop and embedded computing that lingers to this day, but it’s fair to say that the market for it has dwindled. If you have a retrocomputer then, what’s to be done? If you’re [Dean Netherton], you create a processor card for the popular RC2014 retrocomputer backplane, carrying the eZ80, a successor chip that’s still in production.
The eZ80 can be thought of as a Z80 system-on-chip, with microcontroller-style peripherals, RAM, and Flash memory on board. It’s much faster than the original and can address a relatively huge 16MB of memory. For this board, he’s put the chip on a processor daughterboard that plugs into a CPU card with a set of latches to drive the slower RC2014 bus. We can’t help drawing analogies with some of the 16-bit upgrades to 8-bit platforms back in the day, which used similar tactics.
If you buy WS2812s under the Adafruit NeoPixel brand, you’ll receive the advice that “An 8 MHz processor” is required to drive them. “Challenge Accepted!“, says [ShielaDixon], and proceeded to first drive a set from the 7.3 MHz Z80 in an RC2014 retrocomputer, and then repeat the feat from a 3.5 MHz Sinclair ZX Spectrum.
The demos in the videos below the break are all programmed in BASIC, but she quickly reveals that they call a Z80 assembler library which does all the heavy lifting. There’s no microcontroller behind the scenes, save for some glue logic for address decoding, the Z80 is doing all the work. They’re all implemented on a pair of RC2014 extension cards, a bus that has become something of a standard for this type of retrocomputer project.
So the ubiquitous LEDs can be addressed from some surprisingly low-powered silicon, showing that while it might be long in the tooth the Z80 can still do things alongside the new kids. For those of us who had the Sinclair machines back in the day it’s particularly pleasing to see boundaries still being pushed at, as for example in when a Z80 was (almost) persuaded to have a protected mode.
[Joshua Coleman] likes to design his own computers. Sometimes, that means drawing up bus architectures, memory maps and I/O port pinouts. Other times, he can focus his efforts more on the general aesthetics, as well as on building a great set of peripherals, as he shows in his latest ColemanZ80 project. Thanks to the RC2014 architecture defining most of the essential features of a classic Z80 computing platform, [Joshua] was able to design a modern retrocomputer that’s not only genuinely useful, but also looks as if it came off a production line yesterday.
The external design is a sight to behold: bright red laser-cut acrylic pieces form a neat, semi-transparent case with ventilation slots on the sides and lots of blinkenlights on the front. Inspired by 1970s classics like the Altair 8800, the front panel gives the user a direct view of the machine’s internal state and allows simple command inputs through a series of tumbler switches. The CPU, RAM and other basic devices are housed in one case, with all the expansion modules in a second one, linked to the mainboard through a 40-wire flatcable.
Lots of classic chips, but also loads of hand-routed wires grace the ColemanZ80’s mainboard.
Although the mainboard closely follows the RC2014 design, [Joshua] went through a lot of effort to tune the system to his specific needs. The expansion boards he built include an NS16550 UART to replace the default 68B50, a battery-backed real-time clock, a YM2149-based sound card and even a speech synthesizer module built around the classic SP0256 chip, of Speak & Spell fame. An even more unusual feature is the presence of an AM9511, one of the earliest math coprocessors ever made, to speed up floating-point calculations. All of these modules were built entirely by hand on prototype boards: we can barely imagine how much time this must have taken.
Output devices include a VGA adapter courtesy of a Raspberry Pi Pico as well as a regular 4-digit 7-segment LED display and a set of classic HP “bubble” LEDs. [Joshua] runs several demos in his video (embedded below), ranging from computing the Mandelbrot set to playing chiptunes on the YM2149. There’s plenty of scope for further expansion, too: [Joshua] plans to build more peripherals including a floppy drive interface and a module to operate a robotic car.
The hobbyists of the early days of the home computer era worked wonders with the comparatively primitive chips of the day, and what couldn’t be accomplished with a Z80 or a 6502 was often relegated to complex designs based on logic chips and discrete components. One wonders what these hackers could have accomplished with the modern components we take for granted.
Perhaps it would be something like this minimal serial terminal for the current crop of homebrew retrocomputers. The board is by [Augusto Baffa] and is used in his Baffa-2 homebrew microcomputer, an RC2014-esque Z80 machine that runs CP/M. This terminal board is one of many peripheral boards that plug into the Baffa-2’s backplane, but it’s one of the few that seems to have taken the shortcut of using modern microcontrollers to get its job done. The board sports a pair of ATmega328s; one handles serial communication with the Baffa-2 backplane, while the other takes care of running the VGA interface. The card also has a PS/2 keyboard interface, and supports VT-100 ANSI escapes. The video below shows it in action with a 17″ LCD monitor in the old 4:3 aspect ratio.
We like the way this terminal card gets the job done simply and easily, and we really like the look of the Baffa-2 itself. We also spied an IMSAI 8080 and an Altair 8800 in the background of the video. We’d love to know more about those.
The RC2014 is a slick Z80 computer kit that’s graced these pages a number of times in the past. It allows anyone with a soldering iron and a USB-to-serial adapter to experience the thrill of early 1980s desktop computing. But what if you’re looking for an even more vintage experience? In that case, this custom RC2014 front panel from [James Stanley] might be just the thing to scratch that Altair itch.
The front panel allows you to view and alter the contents of memory with nothing more complex than toggle switches and LEDs, just like on the early microcomputers of the 1970s. If you’ve ever wanted to learn how a computer works on the most basic level, single-stepping through instructions and reading them out in binary is a great way to do it.
[James] says he was inspired to take on this project after reading a 1978 issue of Kilobaud Magazine (as one does), and seeing an article about building a homebrew Z80 machine with a front panel. Obviously he had to modify the approach a bit to mate up with this relatively modern variation on the venerable CPU, but the idea was essentially the same.
His documentation for the project is sure to be fascinating for anyone enamored with those iconic computers of yesteryear, but even readers with more modern sensibilities will likely find some interesting details. The way [James] coaxes the data and various status states out of the kit computer takes up the bulk of the write-up, but afterwards he talks about how he designed the PCB and wraps up with his tips for creating a professional looking front panel.
At the end of August I made the trip to Hebden Bridge to give a talk at OSHCamp 2019, a weekend of interesting stuff in the Yorkshire Dales. Instead of a badge, this event gives each attendee an electronic kit provided by a sponsor, and this year’s one was particularly interesting. The RC2014 Micro is the latest iteration of the RC2014 Z80-based retrocomputer, and it’s a single-board computer that strips the RC2014 down to a bare minimum. Time to spend an evening in the hackerspace assembling it, to take a look!
It’s An SBC, But Not As You Know It!
The kit contents
The kit arrives in a very compact heat-sealed anti-static packet, and upon opening was revealed to contain the PCB, a piece of foam carrying the integrated circuits, a few passives, and a very simple getting started and assembly guide. The simplicity of the design becomes obvious from the chip count, there’s the Z80 itself, a 6850 UART, 27C512 ROM, 62256 RAM, 74HCT04 for clock generation, and a 74HCT32 for address decoding. The quick-start is adequate, but there is also a set of more comprehensive online instructions (PDF) available.
I added chip sockets and jumpers to my kit.
Assembly of a through-hole kit is hardly challenging, though this one is about as densely-packed as it’s possible to make a through-hole kit with DIP integrated circuits. As with most through-hole projects, the order you pick is everything: resistors first, then capacitors, reset button and crystal, followed by integrated circuits.
I’m always a bit shy about soldering ICs directly to a circuit board so I supplemented my kit with sockets and jumpers. The jumpers are used to select an FTDI power source and ROM addresses for Grant Searle’s ROM BASIC distribution or Steve Cousins’ SCM 1.0 machine code monitor, and the kit instructions recommended hard-wiring them with cut-off resistor wires. There was no row of pins for the expansion bus because this kit was supplied without the backplane that’s a feature of the larger RC2014 kits, but it did have a set of right-angle pins for an FTDI serial cable.
Your Arduino Doesn’t Have A Development Environment On Board!
Having assembled my RC2014 Mini and given it a visual inspection it was time to power it up and see whether it worked. Installing the jumper for FTDI power, I attached my serial cable and plugged it into a USB port.
A really nice touch is that the Micro has the colours for the serial cable wires on the reverse side of the PCB, taking away the worry of getting it the wrong way round. A quick screen /dev/ttyUSB0 115200 to get a serial terminal from a bash prompt, hit the reset button, and I was rewarded with a BASIC interpreter. My RC2014 Micro worked first time, and I could straight away give it BASIC commands such as PRINT "Hello World!" and be rewarded with the expected output.
The SCM ROM monitor.
So I’ve built a little Z80 single board computer, and with considerably less work than that required for the fully modular version of the RC2014. Its creator Spencer tells me that the Micro was originally designed as a bargain-basement RC2014 as a multibuy for workshops and similar activities, being very similar to his RC2014 mini board but without provision for a Pi Zero terminal and a few other components. It lacks the extra hardware required for a more comprehensive operating system such as CP/M, so I’m left with about as minimal an 8-bit computer as it’s possible to build using parts available in 2019. My question then is this: What can I do with it?
So. What Can I Do With An 8-bit SBC?
My first computer was a Sinclair ZX81, how could it possibly compare this small kit that was a giveaway at a conference? Although the Sinclair included a black-and-white TV display interface, tape backup interface, and keyboard, the core computing power was not too far different in its abilities from this RC2014 Micro — after all, it’s the same processor chip. It was the platform that introduced a much younger me to computing, and straight away I devoured Sinclair BASIC and then went on to write machine code on it. It became a general-purpose calculation and computing scratchpad for repetitive homework due to the ease of BASIC programming, and with my Maplin 8255 I/O port card I was able to use it in the way a modern tech-aware kid might use an Arduino.
The RC2014 Micro is well placed to fill all of those functions as a BASIC and machine code learning platform on which to get down to the hardware in a way you simply can’t on most modern computers, and though the Arduino represents a far more sensible choice for hardware interfacing there is also an RC2014 backplane and I/O board available for the Micro’s expansion bus should you wish to have a go. Will I use it for these things? It’s certainly much more convenient than its full-sized sibling, so it’s quite likely I’ll be getting my hands dirty with a little bit of Z80 code. It’s astounding how much you can forget in 35 years!
The RC2014 Micro can be bought from Spencer’s Tindie store, with substantial bulk discounts for those workshop customers. If you want the full retrocomputer experience it’s a good choice as it provides about as simple a way into Z80 hardware and software as possible. The cost of simplicity comes in having no non-volatile storage and in lacking the hardware to run CP/M, but it has to be borne in mind that it’s the bottom of the RC2014 range. For comparison you can read our review of the original RC2014, over which we’d say the chief advantage of the Micro is its relative ease of construction.
