Review: The RC2014 Z80 Computer

As hackers and makers we are surrounded by accessible computing in an astonishing diversity. From tiny microcontrollers to multi-processor powerhouses, they have become the universal tool of our art. If you consider their architecture though you come to a surprising realisation. It is rare these days to interface directly to a microprocessor bus. Microcontrollers and systems-on-chip have all the functions that were once separate peripherals integrated into their packages, and though larger machines such as your laptop or server have their processor bus exposed you will never touch them as they head into your motherboard’s chipset.

A few decades ago this was definitely not the case. A typical 8-bit microprocessor of the 1970s had an 8-bit data bus, a 16-bit address bus, and a couple of request lines to indicate whether it wanted to talk to memory or an I/O port. Every peripheral you connected to it had to have some logic to decode its address and select it when you wanted to use it, and all shared the processor’s bus. This was how those of us whose first computers were the 8-bit machines of the late 1970s and early 1980s learned the craft of computer hardware, and in a world of Arduino and Raspberry Pi this now seems a lost art.

The subject of today’s review then provides a rare opportunity for the curious hardware hacker to get to grips with a traditional microprocessor bus. The RC2014 is a modular 8-bit computer in which daughter cards containing RAM, ROM, serial interface, clock, and Z80 processor are ranged on a backplane board, allowing complete understanding of and access to the workings of each part of the system. It comes with a ROM BASIC, and interfaces to a host computer through a serial port. There is also an ever-expanding range of further peripheral cards, including ones for digital I/O, LED matrixes, blinkenlights, a Raspberry Pi Zero for use as a VDU, and a small keyboard.

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Talking DIY Z-80 Retrocomputer Complete with Dev Tools

[Scott Baker] wanted to take on a new retrocomputing project. He decided to build an RC2104. Lucky for us, he documented everything along the way. In addition to the main board, [Scott] built bus monitoring and debugging tools, a front panel, a real time clock, an analog to digital converter, and a speech synthesizer.

You can follow along in the 8-part post that includes videos. He started with the basic kit:

  • CPU – The Z80
  • ROM – 27C512 64 KB ROM, selectable in 8KB banks
  • RAM – 62256 32 KB RAM
  • Clock – 7.3728 Mhz crystal that drives a 74HC04 hex inverter (for the CPU and the UART)
  • Serial I/O – MC68B50 UART

In addition, he picked up a digital I/O board.

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Smallest BASIC Computer?

This may be the most minimal computer that we’ve ever seen running BASIC. Hackaday.io user [Kodera2t] has been working through the history of computing, so after his 4-bit CPU, he stepped up his game to eight bits. It’s amazing how much can be done with so little. It’s basically a Z80 on a single PCB.

[Kodera2t] is careful to give credit where credit is due: the design of this computer is by [Grant Searle]. It’s amazing what you can do with an old CPU (6809), some SRAM, a controller-interface chip, and an EPROM for your BASIC. Check out the GitHub for the computer’s PCB files if you want to make your own — it’s a very hobbyist-friendly two-layer board with fat traces. Or you could put it all together on a breadboard. It’s that non-critical.

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The other sweet touch is this monochrome CRT build that pairs up with the tiny computer.

[Kodera2t] is doing some really clever retro and minimalistic hacks, and putting them all up on Hackaday.io. You should really give his whole portfolio a look. We recently wrote up his experimentations with the Atmel ATtiny10 if you’re in the mood for something more modern.

The Dual-Core, ARM-Powered Commodore 64

There is no CPU that is better understood than the 6502 and its cousins the 6510, 6507, 6509, and whatever we’re calling the CPU in the NES. With this vast amount of documentation, just about anything can be done. Want a discrete and un-discreet 6502? Sure thing. It’s the NMOS version, though. Want an emulated version. Sure. With libraries porting the 6502 to every platform ever, there’s only one place left to go: putting a 6502 in a Commodore 64. Make it dual-core, too, so we can run CP/M.

This build is based on one of [telmomoya]’s earlier builds – a soft-core 6510 running on an ARM Cortex M3. The inspiration for this build came from a 6502 emulator running on an Arduino, which got [telmomoya] wondering what would happen if he attached some external RAM, CIA or a SID. Doing this on an Arduino is hard, but there are a few 5 Volt tolerant ARM chips out there, and with a few banks of SRAM, [tel] quickly had an emulated 6502 running EhBasic.

Running an emulated 6502 on an ARM chip is nothing new. What makes this build spectacular is the adaptation to the C64 motherboard. Since [telmomoya] was already breaking out the data and address lines to go to the SRAMs, it didn’t take much extra work to simply build an adapter for the DIP40 CPU socket on a C64. A few 74-series logic chips made the interface easy, and after a bit of soldering, [telmomoya] had a Commodore 64 powered by an ARM chip.

If you’re emulating one chip, you can emulate two, and with the Commodore 64, this leads to a few interesting possibilities. The C64 had a CP/M cartridge — a cartridge that contained a Z80 CPU, sharing the data and address bus with the 6510. This cartridge allowed the ‘toy computer’ C64 to run the ‘business’ CP/M operating system (and the Z80 made the Commodore 128 much cooler).  Since [telmomoya] was already emulating a CPU, emulating a second CPU wasn’t really that hard.

It’s a phenomenal build, and great if you’ve ever wanted to speed up VisiCalc.

Who Needs the MSP430 When You Have TI’s Other Microcontroller, The TI-84?

We’re sure there are more expensive LED controllers out there, but the TI-84 has got to be up there. Unless you have one on hand, then it’s free. And then you’ll doubtless need an SPI library for the famously moddable graphing calculator.

[Ivoah] is using his library, written in assembly for the Z80 processor inside the TI, to control a small strip of DotStar LEDs from Adafruit. The top board in the photograph is an ESP8266 board that just happened to be on the breadboard. The lower Arduino is being used as a 5V power supply, relegated to such duties in the face of such a superior computing device.

Many of us entertained ourselves through boring classes by exploring the features of TI BASIC, but this is certainly a step above. You can see his code here on his GitHub.

After his proof-of-concept, [Ivoah] also made a video of it working and began to program a graphical interface for controlling the LEDs. Video after the break.

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Breadboard Colecovision

The Colecovision was a state-of-the-art game console back in 1983. Based around the Z-80, it was almost a personal computer (and, with the Adam add-on, it could serve that function, complete with a daisy wheel printer for output). [Kernelcrash] set out to recreate the Colecovision on a breadboard and kept notes of the process.

His earlier project was building a Funvision (a rebranded VTech Creativision) on a breadboard, so he started with the parts he had from that project. He did make some design changes (for example, generating separate clocks instead of using the original design’s method for producing the different frequencies needed).

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Winning the Console Wars – An In-Depth Architectural Study

From time to time, we at Hackaday like to publish a few engineering war stories – the tales of bravery and intrigue in getting a product to market, getting a product cancelled, and why one technology won out over another. Today’s war story is from the most brutal and savage conflicts of our time, the console wars.

The thing most people don’t realize about the console wars is that it was never really about the consoles at all. While the war was divided along the Genesis / Mega Drive and the Super Nintendo fronts, the battles were between games. Mortal Kombat was a bloody battle, but in the end, Sega won that one. The 3D graphics campaign was hard, and the Starfox offensive would be compared to the Desert Fox’s success at the Kasserine Pass. In either case, only Sega’s 32X and the British 7th Armoured Division entering Tunis would bring hostilities to an end.

In any event, these pitched battles are consigned to be interpreted and reinterpreted by historians evermore. I can only offer my war story of the console wars, and that means a deconstruction of the hardware.

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