The Zilog Z80 is an 8-bit microprocessor designed and sold by Zilog from July 1976 onwards . My personal goal is to design and build a fully functioning Z80 based computer, including implementation of graphics, sound and other interfaces from both discrete logic and microcontrollers. At present not much has been done other than brainstorming, however this should pick up steam throughout summer 2010.
A 'motherboard' which allows for incremental development and for new features to be added at a later date.
PIC and AVR microcontrollers may not be fast enough to generate timing signals for the display and rich graphics, however the Propellor has 8 cores, which can be devoted to different tasks. Is it right to have a video controller that is a lot more powerful than the main CPU?
FPGAs are awesome. An FPGA graphics controller will give lots of flexibility and room for expansion - plus I could offload a lot of the other tasks to it!
Ethernet controller (Microchip ENC28J60)
Proprietary wireless controller (another PIC?)
Timing circuits controllable in software, ie software overclocking
Would only require a PIC with a small address space
Expansion cards given fixed address space, first chunk is EEPROM with 'drivers'
Dual processor (in the futher future?)
Each processor has it's own memory, and a shared piece of memory
Some intermediate memory controller to allow both to access all memory
I currently have ZX80 circuit diagrams. When I have a significant chunk of spare time, I will start looking into creating some timing circuits, and a power supply. The focus will then move onto the basic CPU / RAM / ROM heart of the project. Once these are done, the fun can begin!
For now, this project will be going on hold. I'd love to say I have the time and expertise to complete it, but I think that it'd take me too much time to be able to do this whilst doing other projects. This is by no means forever, it has become a life goal for me to do this project, and once I have a few more skills under my belt, I will really get stuck in.
Grant Searle has reproduced the original circuit diagram of the ZX80 here, which I will be using to base the timing circuits, and possibly build a rudimentary graphics circuit to test with.