Retro Serial Terminal Uses Modern Chips To Get CP/M Machine Talking

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.

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CRISS CP/M Provides Modern Hardware For A Classic OS

Today you might choose run Windows, Linux, MacOS or some other OS on your computer. Back in the 1980s however, you generally had little choice: a certain home computer came with a certain OS, and that was it. If yours was based on a Z80 processor, chances are it ran CP/M. While differences in hardware often made direct data exchange difficult, CP/M provided at least a basic level of software compatibility between various Z80-based computers. Although eventually supplanted by MS-DOS (which initially aimed to be compatible with CP/M), enthusiasts kept the classic OS running on old hardware throughout the 90s and even beyond.

[Igor] decided to make a 21st-century CP/M machine by designing the CRISS, a single-board computer based mainly on AVR microcontrollers. The CPU is a 20 MHz ATMEGA1284P, which imitates a 4 MHz Z80 through machine-code emulation. A pair of ATMEGA328s run the peripheral controller and a VGA output, so the CRISS can be used with modern monitors. True to its heritage however, the image is monochrome green-on-black, looking instantly familiar to users of Kaypros, Osbornes and other contemporary CP/M machines.

Software is loaded through an SD card that holds floppy images. The CRISS can directly run programs written for the Kaypro II and Robotron 1715 computers, although other platforms can be supported as well with a software upgrade. [Igor] shows it running programs ranging from the Turbo Pascal compiler to games like Xonix and Tetris.

Housed in a neat little case, the CRISS can communicate with standard PS/2 keyboards and serial printers. Even an Ethernet port is provided for those willing to experiment with network connectivity (a rare feature in the 1980s).

We love seeing modern retro builds like this; similar projects we’ve covered before include the compact ZZ80MB and the huge Z20X. Others have used different ways of running CP/M on modern hardware, such as booting it directly on a Raspberry Pi or emulating an Altair on an ESP32.

Translate Your CP/M Code To 8086, And Leave The 1970s Behind!

“Bring our home computing out of the 1970s and into the 1980s and beyond” is the irresistible promise made by the creator of 8088ify, a piece of software which translates CP/M executables from their 8080-based originals to assembler code that should run on an 8088 under MS/DOS. How can we resist such a futuristic promise here in 2021, even though the code wasn’t written to the sound of Donna Summer or the Village People back in the day but here in 2021 for PCjam, a celebration of the original IBM PC’s 40th anniversary.

As the writer of this code [ibara] points out that Intel intended the 8088 to be a ready upgrade path for the 8080, and designed its instruction set while not directly compatible, to make translation between the two a straightforward process. There was commercial software for the task at the time, but to this day there remained nothing with an open-source licence. It’s written in ANSI C for portability across platforms and compilers, and can even be compiled under CP/M itself.

PCjam is well worth a look, and if any of you fancy a go at writing for the earliest MS-DOS machines we’d like to suggest you create something for it. Meanwhile if you’d like to explore CP/M, you can run a bare metal emulator on the Raspberry Pi.

Header: Thomas Nguyen, CC BY-SA 4.0.

Apple Gets CP/M

In case you wanted to run WordStar on your Mac, [Tom Harte] offers CP/M for OS/X, and it looks like it would be a lot of fun. Of course you might be happier running Zork or Turbo Pascal, and you can do that, too.

There are plenty of Z80 emulators that can run CP/M, but what we found most interesting about this one is that it is written in Objective C, a language with a deep history in the Mac and NeXT worlds.

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This Z80 Computer Bootstraps Itself

[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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ESP32 Altair Emulator Gets Split Personality

If you wanted me to demo CP/M running on an emulated Altair 8800, I’d pull out a tiny board from my pocket. You might wonder how I wound up with an Altair 8800 that runs CP/M (even WordStar), that fits in your pocket and cost less than $10. Turns out it’s a story that goes back to 1975.

When the Altair 8800 arrived back in 1975, I wanted one. Badly. I’d been reading about computers but had no hands-on experience. But back then, as far as I was concerned, the $400 price tag might as well have been a million bucks. I was working for no real pay in my family’s store, though in all fairness, adjusted into today’s money that was about $2,000.

I’d love to buy one now, but a real Altair costs even more today than it did back then. They also take up a lot of desk space. Sure, there are replicas and I’ve had a few. I even helped work the kinks out of Vince Briel’s clone which I’ve enjoyed. However, the Briel computer has two problems. First, it takes a little work to drive a serial port (it uses a VGA and a PS/2 keyboard). Second, while it’s smaller than a real Altair, it is still pretty large — a byproduct of its beautiful front panel.

So to quickly show off CP/M to someone, you need to haul out a big box and find a VGA monitor and PS/2 keyboard — both of which are becoming vanishing commodities. I made some modifications to get the serial port working, but it is still a lot to cart around. You could go the software route with a simulator like SIMH or Z80pack, but now instead of finding a VGA monitor and a PS/2 keyboard, you need to find a computer where you can install the software. What I really wanted was a simple and portable device that could boot CP/M.

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Portable CP/M Runs The Classics Anywhere

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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