Interfacing A Z80 CPU With The Raspberry Pi

February 9, 2021 by Lewin Day 25 Comments

The Z80 was a big deal in the 1970s and 1980s, and while its no longer a dominant architecture today, its legacy lives on. [James Andrew Fitzjohn] is a fan of the Z, and decided to interface the real silicon with the Raspberry Pi, by and large for the fun of it!

The Z80’s address and data lines, as well as the clock, are hooked up to the Raspberry Pi through several MCP23017 GPIO expanders. The Pi’s GPIO lines aren’t known for their speed, of course, and using expanders through I2C isn’t exactly quick either. However, speed isn’t necessary, as the clock only goes as fast as the Raspberry Pi desires, since it’s controlling the clock along with everything else. There’s also an LCD for viewing the Z80s status, along with some era-appropriate blinkenlights.

This setup allows the Pi to run code directly on the Z80 itself, while managing the CPU’s RAM in its own memory, all through a Python script. It’s a fun hack that lets you run retro code on retro silicon without using an emulator. Techniques like these are useful for finding undocumented or edge case performance of a processor. If this hack isn’t enough Zilog for your liking, consider throwing one in your pocket as well!

A Lambda 8300 Lives Again

December 10, 2020 by Al Williams 3 Comments

If you follow retrocomputing — or you are simply old enough to remember those days — you hear the same names over and over. Commodore, Apple, Radio Shack, and Sinclair, for example. But what about the Lambda 8300? Most people haven’t heard of these but [Mike] has and he has quite a few of them. The computer is similar to a Sinclair ZX81, but not an exact clone. All of his machines need some repairs (he’s promised repair videos are on their way), but for the video below he wired a monitor directly to the PCB to get steady output, so apparently the RF modulator is the failing subsystem in this case.

Once the video cleared up, you can see a walkthrough of running a simple BASIC program. As was common in those days, the computer used an audio cassette recorder for data storage. [Mike] picked up some dedicated recorders meant for computer use, but neither were in working shape. However, a consumer player works fine.

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This Z80 Computer Bootstraps Itself

October 28, 2020 by Al Williams 32 Comments

[Plasmode] has created several Z80-compatible board designs, at least four of them using the oddball Z280. The Z280 was a special variant of a Z80 that could bootstrap itself with no external PROM, making it ideal for anyone trying to build a system on a breadboard. According to his post, the cost to build the board is about $35.

Although the 8080 CPU got a lot of glory, it was much harder to use than the Zilog Z80. The Z80 only required a single clock and power supply, so it was much easier to build a system, even on a breadboard. On top of that, the bus wasn’t multiplexed and it could refresh DRAM memory by itself. Maybe that’s why you can still get Z80-derived chips readily. There was one thing, though, you needed an EPROM or some other way to run some initial code to bootstrap your system. Zilog knew this was a problem. In those days, you had to use a special tool to burn a PROM and, unless it was erasable and you had the special UV light to erase it, any mistakes cost you a chip.

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Iconic Yugoslavian Galaksija Computer Reborn, With A Documentary Too

October 25, 2020 by Jenny List 21 Comments

One of the humbling things about writing for Hackaday is the breadth of experience among our colleagues, despite one’s own skills or achievements there is probably for all of us a level of impostor syndrome when we look at their work. This week provided a reminder of this, while taking a closer look at the crowdfunder for a documentary about the Galaksija, the Yugoslavian 8-bit computer from the 1980s designed by our colleague [Voja Antonić]. Not only will the documentary be produced, but also they are recreating the Galaksija as a kit, so you can experiment with this historic computer for yourself. The campaign has reached passed its goal a couple times over but still has a few days left, so jump in if you are interested.

Freshly made original Galaksija (top), and new double-sided Galaksija (bottom).

With the advantage of being able to reach out to [Voja] as a colleague, it was time to secure the straight dope on the project. Though he’s not spearheading it, aside from appearing in the documentary he’s also produced the new Galaksija PCB to take advantage of double-sided manufacture and remove the wire links that were a feature of the original.

In that sense this isn’t so much a clone of the original as an updated version from the same designer, with only a few other updates such as key switches and connectors where the exact original component could no longer be sourced. A particularly fascinating side-tale comes from a reprint of the first Galaksija magazine. Photo-reproductions of the original printed pictures did not yield good results, so [Voja] built from scratch an entirely original Galaksija, carefully recreating the framing of each step shown in those original photos.

This project has faced its fair share of obstacles before launching on Crowd Supply, so it’s very good indeed to see it receive its funding with time to spare. We look forward to seeing the results, meanwhile you can see a promo video in Serbian with Youtube’s English subtitling below the break. You can read [Voja]’s writing on the machine in Hackaday articles past, but don’t miss the opportunity to meet him at a live event — he’s the mastermind behind a number of hardware badges at Hackaday events.

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Portable CP/M Runs The Classics Anywhere

July 23, 2020 by Al Williams 19 Comments

If you want to run an old CP/M program — maybe you want to run WordStar or play StarTrek — you have several options. One is to acquire some classic hardware. You can also build a new computer using a Z80 or some other processor that will emulate a Z80. Finally, you can emulate old hardware on your current computer. The iz-cpm project from [ivanizag] takes this last approach. Unlike some emulators, iz-cpm doesn’t try to emulate everything in one simulated environment. Instead, it directly accesses your file system so it allows CP/M executables to run more as though they were a native program.

You can think of it as Wine for CP/M. The code is portable to Linux, Windows, or MacOS. The author mentions, though, that it won’t run on CP/M itself! The program can run an executable standalone which means you could set .COM files up to execute automatically if you wanted to.

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Grok The Z80 With This Simulator

July 20, 2020 by Jenny List 18 Comments

Many of us will have at some point encountered a Z80 microprocessor, whether we’ve bare-metal programmed for it, or simply had a go at blasting some invaders on a game system using one. Like all the processors of its era, it’s got a relatively simple and accessible internal block diagram, so there’s a good chance that readers well even know how it works, too. But do any of know how it really works, down to the gate, transistor, and net level? [Goran] does, because he’s written a Z80 netlist simulator that allows the running of code alongside the examination of the chip and its signals. It’s not particularly fast, achieving a modest 2.3kHz clock speed when run of a fairly high-end PC, but we’re guessing readers needing to run Z80 code for anything other than learning would use the real thing anyway.

There’s a video of the software in operation which we’ve placed below the break, and we can see it will be a fascinating tool even to people who aren’t dedicated reverse engineers. To be able to bring up a logic analyzer view of the internals of a processor while it is in operation is truly astounding if you are used to it as a black box, and to have logic diagrams at your fingertips rather than puzzling out individual transistors really gives a window into what is going on.

This isn’t the only such simulator out there, in the past we’ve mentioned Visual6502, when we covered the Monster 6502.

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A Z80 Board With Very Few Parts

July 17, 2020 by Al Williams 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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