z80

118 Articles

Protected Mode On A Z80! (Almost)

October 23, 2022 by 27 Comments

The microprocessor feature which probably most enables the computing experience we take for granted today is protected mode. A chip with the required hardware can run individual software processes in their own environments, enabling multitasking and isolation between processes. Older CPUs lacked this feature, meaning that all the resources were available to all software. [Andy Hu] has done the seemingly impossible with a Zilog Z80, enabling a protected mode on the chip for the first time in over four decades. Has he found an elusive undocumented piece of silicon missed by every other researcher? Not quite, but it is a clever hack.

The Z80 has two address spaces, one for memory and the other for I/O. He’s taken the I/O request line and fed it through a flip-flop and some logic to call a hardware interrupt the first time an I/O call is made or when a RST instruction is executed. Coupled with a small piece of memory for register contents, and he’s made a Z80 with a fully-functional protected mode, for the cost of a few logic chips. It’s explained in the video below the break, and we hope you agree that it’s rather elegant given the resources in hand. It’s too late for the commercial 8-bit machines of the past, but it would be interesting to see what today’s retrocomputer designers make of it.

Continue reading “Protected Mode On A Z80! (Almost)” →

A small keyboard form factor retrocomputer with blue keys on a black background sits in front of a display and a LEGO model of the Space Shuttle. There are a number of jumper wires and a breadboard coming from an open panel on the right side of the machine.

Aqua PCB Is A Big Upgrade For The Mattel Aquarius

October 15, 2022 by 9 Comments

In case you weren’t around in the 80s, or you happened to blink, you may have missed the Mattel Aquarius computer. [Nick Bild] has a soft spot in his heart for the machine though and built the Aqua cartridge to make the Aquarius into a more usable machine.

Originally equipped with a mere 4 KB of RAM and a small, rubbery keyboard, it’s not too surprising that the Aquarius only lasted five months on the market. [Nick] decided on the cartridge slot to beef up the specs of this little machine given the small number of expansion ports on the device. Adding 32 KB of RAM certainly gives it a boost, and he also designed an SD card interface called Aqua Write that connects to the Aqua cartridge for easily transferring files from a more modern machine.

The Aqua Write uses an Arduino Mega 2560 to handle moving data between the SD card and the system’s memory. This is complicated somewhat because a “PLA sits between the Z80 and data bus that XORs data with a software lock code (initialized to a random value on startup).” [Nick] gets around this by running a small program to overwrite the lock code to zero after startup.

Getting data on and off retrocomputers can certainly be a challenge. If you’re trying to get files on or off another old machine, check out this Simple Universal Modem or consider Using a Raspberry Pi as a Virtual Floppy Drive.

TRS-80 Model II Lives Again

September 17, 2022 by 15 Comments

A lot of people had a Radio Shack TRS-80 Model I. This was a “home computer” built into a keyboard that needed an external monitor or TV set. Later, Radio Shack would update the computer to a model III which was a popular “all in one” option with a monitor and even space for — gasp — floppy disks. But the Model II was not nearly as common. The reason? It was aimed at businesses and priced accordingly. [Adrian] got a Model II that was in terrible shape and has been bringing it back to life. You can see the video of how he’s done with it, below.

The Model II was similar to the older “Trash 80” which had been used — to Radio Shack’s surprise — quite often by businesses. But it had more sophisticated features including a 4MHz CPU — blistering speed for those days. It also had an 80×25 text display and a 500K 8-inch floppy drive. There were also serial and printer ports standard.

There were a few interesting features. The floppy drive’s spindle ran on AC power and if the computer was on, the disk was spinning. In addition, there was bank switching so you could go beyond 64K and also you didn’t have to share your running memory with the video display. In theory, the machine could go beyond 64K since half the memory was bank switchable. In practice, the early models didn’t have enough expansion space to handle more than 64K physically.

Continue reading “TRS-80 Model II Lives Again” →

Z80 Single-Board Computer Looks Like It Could Have Been A Killer Product

August 20, 2022 by 30 Comments

Most retrocomputer builds seem to focus on either restoring old machines or rebuilding them from scratch. Either way, the goal is to get as close as possible to the original machine, and while we certainly respect those builds, there are other ways to celebrate the computers of yesterday, as this Z80 single-board computer nicely demonstrates.

[Ivan Farafontov]’s SBC is sort of a “Z80 that never was” build, one that would almost have been possible back in the heyday of 8-bit computing, and would have made quite a splash if it had. Most of the peripheral chips are from Zilog and would have been found in many of the Z80 machines of the day, like the TRS-80 and ZX Spectrum. Where it goes off the old-school path is with the video section, which uses an Atmel CPLD chip and a dual-port RAM to drive a VGA monitor. It still looks the part, though, with a 256×192 pixel, 16-color display. The compact video section helps keep the overall footprint of this machine pretty small, at least by the standards of the old machines. The machine is barely larger than its custom keyboard, which is populated with mechanical switches and really nice-looking custom keycaps, and everything fits into a 3D-printed case.

The demo that starts at the 4:30 mark of the video below will be a nostalgia storm for a lot of readers, starting as it does with a version of Boulder Dash that [Ivan] wrote from scratch, along with the tile editor he used to create the sprites for the game. All the design files and code are available if you want to build your own, of course. We recently featured another Z80 that never was, but [Ivan]’s machine really makes a statement with its compact size and its capabilities.

Continue reading “Z80 Single-Board Computer Looks Like It Could Have Been A Killer Product” →

Modular Z80 Really Racks Up The Retrocomputer Cred

July 19, 2022 by 24 Comments

Very few retrocomputing projects are anything other than a labor of love. There’s really no practical reason to build a computer that is woefully inadequate for just about any task compared to even an entry-level PC today. But the lack of a practical reason to do something rarely stops a hacker, as with this nifty modular Z80-based rack computer.

Actually, there’s at least one area where retrocomputers excel compared to their modern multi-core gigahertz counterparts — and that’s nostalgia. That’s what [Ricardo Kaltchuk] was going for with his build, which started by finding a Z80 and an Intel 8251 USART in his parts bin. Those formed the core of what would become the “Proton” computer, a modular beauty built around 7 cm by 10 cm PCBs that plug into a backplane inside a rack made from aluminum angle. Aside from the power supply and the Z80 CPU, other modules include a RAM card with a zero insertion force socket for an EPROM, a mass-storage module sporting a 128 MB Compact Flash card, plus modules for standard serial and I2C comms.

The fit and finish are excellent, and the performance is impressive. The Proton runs CP/M and boasts a ton of old applications that will bring back some memories, like SuperCalc and dBase. We’d venture a bet that WordStar is in there someplace, or easily could be. The video below is a little rough, but shows everything off really well.

In some ways, the Proton reminds us of the RC2014, but its fit and finish are what bring this build home. That’s not to take away from the work [Ricardo] obviously put into documentation, though. The 62-page manual has every detail of every module, plus instructions for building one of your own.

Continue reading “Modular Z80 Really Racks Up The Retrocomputer Cred” →

CP/M Is Now Freer Than It Was

July 13, 2022 by 32 Comments

It’s easy to think of the earlier history of desktop computing operating systems in terms of DOS, Windows, and Mac OS with maybe a bit of AmigaOS, TOS, or RiscOS thrown in. But the daddy of desktop computing, the OS that put word-processors and spreadsheets in 1970s offices and had a huge influence on what followed, isn’t among that list. Digital Research’s CP/M ran initially on Intel 8080-based machines before losing out to MS-DOS as IBM’s choice for their PC, and then gradually faded away over the 1980s. Its source has been available in some form with a few strings for a long time now, but now we have confirmation from Digital Research’s successor company that it’s now available without restrictions on where it can be distributed.

For years it was something an operating system that had been bypassed by the hardware and hacker communities, as the allure of GNU/Linux was stronger and most available CP/M capable machines were also 1980s 8-bit gaming platforms. But with the more recent increased popularity of dedicated retrocomputing platforms such as the RC2014 it’s become a more common sight in our community. Brush up your command line skills, and give it a go!

Header: Michael Specht, CC BY-SA 3.0.

A Z80 CPU board built on a piece of prototype board with an edge connector

Designed From Scratch And Fully Handmade: The Modular Coleman Z80 Computer

March 25, 2022 by 34 Comments

While the phrase “I built my own computer” might sound impressive to the uninitiated, anyone with an interest in modern computer hardware knows that there’s really not much to it: buy a case, a motherboard with a CPU, some RAM and peripherals, and you’re pretty much there. What’s way more impressive is designing a complete computer system from the ground up, as [Joshua Coleman] just did when he built the Coleman Z80.

And when we say “from the ground up”, we mean it: everything down to the system bus was hand-drawn by [Joshua] himself. It does share something with modern PCs though: a strictly modular design. There’s a Z80 CPU board, a ROM and RAM board, and even two modules that you could describe as a video card and a sound card. All of these are built on prototyping boards with a 40-pin edge connector and hooked up to a single backplane carrying the main system bus.

Designed as an experimentation platform, the Coleman Z80 has many features that enable testing and debugging, such as an adjustable clock generator and a few beautiful vintage LED displays that show the status of the main bus. Input and output are mainly through a serial link and a 16×2 LCD, but [Joshua] is already planning a keyboard interface and composite video output to give it that proper 1980s home computer vibe. The software is currently limited to a ROM monitor that enables basic I/O commands, but with 256 KB of RAM there’s plenty of potential for writing useful software.

Just as impressive as the design itself is the fact that this was [Joshua]’s first electronic design project; we’ve certainly seen worse first projects! Over the years we’ve featured several cool homebrew Z80 computers, such as a super-minimalistic board, a modular system based on the powerful eZ80, and this cute little one that fits inside an Altoids tin.

Continue reading “Designed From Scratch And Fully Handmade: The Modular Coleman Z80 Computer” →