In 1983 I bought my first book about microprocessors during a summer holiday in Austria, it was titled “Microcomputer selbstgebaut und programmiert” (“Microcomputer self-built and programmed” in English) written by Rolf-Dieter Klein. German television made even a course on it and a lot of the material is still there. Also my thesis was done around the Z80 working on a MPF-1B Z80 trainer. Over the years I kept my plans alive to build/design something myself like that but never got to it. Also in the meantime I did some side-steps to the 6502 processor.
Last year I discovered the RC2014 project / website and got inspired to dig out my old plans make something my own.
Especially in the RC2014 project I like the active online community (which didnt exist in the 80’s) we had real “Computer geek meetings” but they were very local.
What do (did) I like about RDK’s book/modules, and RC2014. First of all its modularity, the RC2014 even more than RDK’s. The “low level entry”, it is almost possible for everyone with some soldering skills to build a Z80 computer, making LED’s , displays, and relays blink and click. Make sound, video boards etc.
What did I do different. The major thing I dont like about RDK’s designs as well as RC2014 is the “wobbly single row connector backplane” (some might shoot me for this statement <Grin>). And where RDK’s boards were well buffered I see this lacking in the RC2014 design.
So the design criteria for my own system were :
- Eurocard (100x160mm) form factor board with 64-PIN A-C row connector.
- A decent (19″ rack) based backplane.
- All exension boards as well as the CPU board buffered.
- Doesn’t necessarily have to be very low (basic electronics) level, I might use SMD components as well as programmable logic (GAL, CPLD). But everyone with some soldering skills might be able to build it.
What do I NOT intend (to be) :
- Commercial , I am not planning to make a business out of it.
- Being a competitor for RC2014, as said , I very much love the project and community, I do have some other ideas about designing though.
I DO hope to inspire other people tinkering with old school (Z80) processors, peripherals etc. that are still widely available and sometimes even being manufactured.
NDR Kleincomputer by Rolf-Dieter Klein (For those who speak German) : http://www.ndr-nkc.de/compo/index.htm
RC2014 Site : https://rc2014.co.uk/
I agree about the RC2014 system, it is not well designed. I pointed out all the issues with it but many people don’t really want to hear negative comments.
The RDK system has similar issues. Wobbly boards, etc.
Porting RDK to Eurocard solves the mechanical issues but not the electrical ones. If you have a backplane, wires become transmission lines so you must have a known impedance and matching terminators to prevent reflections and ringing. Clamping diodes will prevent overshoot and undershoot.
This is a properly designed bus: https://hackaday.io/project/28936-stebus
It is not tied to any CPU or speed. It addresses all the transmission line issues, multi-master arbitration, etc that other bus standards ignore.
First of all thanks Keith for the reply , your thoughts and the documentation. It’s a thing to think about. And I agree the STE and VME busses are well designed and robust. Especially thanks for sharing the reference material. Already the mechanical definitions are very useful.