<IF you can stick the XT keyboard (are keyboards that talk that protocol
<still being made?) then look at the circuit of the PC or XT. The keyboard
<interface is a few TTL chips hung off an 8255.
At keyboards can be used as well as they are similar (not the same). You'll
have to make a interface as the serial is not compatable with UARTs, also
you will have to convert the key down/Key up codes to something more human.
<I'd make it modular (in that I'd have expansion slots), but I'd probably
<put the CPU + RAM + basic I/O on the 'motherboard'. For prototyping,
<DIN41612 connectors are easier than edge connectors because you don't
<need special boards with the connector fingers on them.
An acceptable bus is ISA-8bit and there are plenty of FDC, VIDEO, HDC cards
for that bus that could easily interface to z80.
<SRAM is a _lot_ easier. And now that 64K SRAM is 2 chips at most (62256's
<are cheap now), I'd use that. DRAM is not too hard until you realise that
<layout and decoupling are critical if you want to avoild random errors.
Same comment, one proviso, if your doing over 256k consider DRAM and MMU.
a good article for that is at the TCJ site.
<[For the hardware wizards here : Yes you can homebrew with DRAM - I've
<done it. But not as my first real project].
For a z80 system of 64 or 128k static is far easier. Also 128kx8 parts are
cheap so even 256k or 512k ram systems are modest.
Allison
Received on Sat Apr 03 1999 - 19:19:20 BST