I want to design and build an 8-bit microcomputer as an intellectual exercise.
I want to brush up on my electronics chops.
Does /g/ have any experience or advice on what CPU I should design it around?
I've narrowed it down to the Zilog Z80, the MOS 6502, the Motorola 6809, or the Intel 8080.
I'm leaning toward the Z80 or the 6502 since their still in production.
>8080 or maybe even 8051
No longer in production.
Better 6502 because Apple, Atari and Commodore all used it and it is very well documented.
It's also very simple and easy to understand since it was designed for appliances like washing machines.
It's easy as shit to find 8080s though, and they're very similar to Z80s.
Both are also going to be very well documented for OP's specific case since they were a mainstay in early S100 and other hobbyist systems.
I looked into it. I was a little put off by the fact the 6502 used the same instructions to access both memory and peripherals.
I'm a little new to design an address decoding logic to separate the operations.
The Z80 on the other hand used separate instructions to access memory and peripherals.
Should I cut my teeth on the Z80 and then move up to the 6502?
the z80 was easier to drive the hardware (fewer glue chips) and the nmemonics were easier to remember. i used the 8031/51 for circuits that needed a higher clock speed. all the chips were ripped from old modems/printers.
the 8751 is a 8051 with a otp (one-time-programmed) rom. you can disable the internal rom and use a external prom by setting a certain pin to vcc or gnd but you lose 2 internal ports in the process.
Z80 is a clear win over the 8080. I think Z80 assembly is comfier than 6502, and you can run open source CP/M which allows you to write drivers for your I/o and then run tons of off the shelf programs.
OTOH the overall community for 6502 is larger because way more 80's computers used it
Are you looking at building it around purely 70's/80's era chips? Or are you willing to use some slightly more modern components, for example instead of TTL logic for address decoding would you want to use a CPLD instead? I know it's not a Z80 or 6502 but check out the 68katy (http://www.bigmessowires.com/68-katy/). I wouldn't cross the 68000 off your list even though it looks a bit intimidating. Working on a 68k computer myself.
I'll admit the temptation to build a 6502 system is appealing because nostalgia. But I like the flexibility of the Z80.
I might progress to that some day. I've never programmed CPLDs before, but if availability or chip-count become an issue I may.
I'm a little hesitant to go 16-bit until I've gotten something relatively simple going.