Of course everyone knows the Raspberry Pi, the ultimate microcomputer board. But there is (much) more under the sun. Such as the special Z80-MBC2 based on a Z80 and a modern microcontroller.
The Z80 microprocessor was a popular 8-bit CPU that had its heyday, especially in the illustrious 1980s. In fact, the Z80 was an extended 8080. That compatibility with Intel’s older 8080 allowed it to run a popular operating system from those days: CP/M. That CP/M was the predecessor of MS-DOS. If there hadn’t been an agreement between IBM and a very young Bill Gates of the then still very young Microsoft, there would have been a huge chance that CP/M would have been the PC operating system for decades to come. Things turned out differently, which meant that in the late 1980s, MS-DOS took over as the most popular OS. However, CP/M has been around for a long time and there is a huge mountain of software available for it. Only: on a modern system, all that beauty no longer runs. Emulate (see image above) is an option, but Z80-MBC2 offers a much nicer solution.
Z80 and Atmel
The Z80-MBC2 is a single board computer based on a Z80. In addition, we also find a (more) modern microcontroller in the form of the Atmel ATMEGA32A at. The software in it replaces a mountain of surrounding chips that were previously necessary to build a Z80 system. The result is a very affordable system. Both the Z80 and the Atmel cost an apple and an egg these days and the handful of other parts are also peanuts. If you want to build the system yourself, it will cost about three to four tens. Includes circuit board and parts. If you do a bit of searching on eBay, interesting offers regularly pop up. We scored a ready-built PCB plus two expansion modules for less than six bucks. The latter are very practical, because they allow you to download all the necessary software from a modern micro-SD memory card. The other module is a real-time clock, which is always handy.
128 kB RAM
The idea is to pay more attention to this system in the near future. For now, as an introduction, we first look at the possibilities. And there are quite a few. However, you must understand that this is a ‘classic’ computer, for which you need an equally classic terminal for access. Or a terminal program. So no graphical fuss, everything is text-based. But yes, that was more than enough for most users at the time. CP/M is also essentially a text-based operating system, so that’s no problem at all. The Z80-MBC2 also has 128 kB of RAM. That would have been a huge amount in the heyday of CP/M. Especially when you consider that the Z80 could actually control a maximum of 64 kB. More was possible via bank switching – the trick that was also used here. But that turned out to be an expensive joke.
Terminal
As mentioned, you use your computer as a terminal (or if you really want to go retro, get yourself a second-hand terminal on eBay, but pay close attention to the signal values. This board is RS232 compatible, but on TTL- level. Most real terminals use voltage levels that far exceed that. So a converter is necessary. If you want to play it safe, buy a USB-to-serial (RS232) TTL converter for a few Euros. There are a lot of them because these are (among other things) used to program microcontrollers.
Collapse OS and UCSD Pascal
Apart from CP/M, Z80-MBC2 also supports Collapse OS, an operating system based on the programming language forth. That Forth is of course also an old-timer, but even today it still offers interesting possibilities on this kind of 8-bit microsystems. Another veteran who also runs effortlessly on the system is UCSD Pascal. Pascal was the ‘elegant’ and structured alternative to Basic. Pascal lives on today and is better known as Delphi. By the way, if you start the system in CP/M mode, then of course more programming languages are available for this operating system. For example, you can go to this site. You will see illustrious programming languages of equally illustrious origins from the gray digital past.
Old and new
Of course, ‘old’ does not mean that the Z80-MBC2 can only be used for retro applications. Admittedly, that will be the most interesting main goal for most users. But keep in mind that the system is nice and energy efficient (a CMOS version of the Z80 is used) and it is therefore no problem to leave it switched on for a long time. In short: what do you care about using the computer to control something? It is precisely the simplicity of the Z80-MBC2 that makes it an accessible whole. However, there is a small hurdle: the computer does not have an Ethernet connection. They didn’t exist at the time, that’s why. But that’s pretty easy to fix. You can buy RS232 serial to Ethernet converters from Chinese manufacturers for less than a tenner. These devices have their own web interface in which you can configure everything as desired. And so you can still use your Z80-MBC2 via a terminal program via the network to approach.
There are also modules (not ordered by us) that allow you to make a serial port available via WiFi and/or Bluetooth. So it doesn’t take a lot of effort to bring an essentially retro system like this into the modern age.
All parts mentioned in this article have already been ordered and received by us. We will definitely come back to it, because you can have a lot of fun with this!