25 Oct
2005
25 Oct
'05
8:28 p.m.
OK, I'm wanting to build a board with an 8 bit CPU
(probably Z80,
possibly 6502) and a floppy controller IC on board with the intention of
hanging it off my PC (via serial or parallel, undecided yet) and
allowing me to read and write *most* formats from various 1980's 8 bit
micros...
Funny, when I asked a few months ago if anyone was interested in
collaborating on doing exactly this, I was practically run off the list
with comments about how impractical it was, nobody would build it,
and wouldn't a catweasel be ever so much better... So I let the idea
drop (still might build one privately however).
Intel's 8271 looks like a possibility at the
moment, but I thought I'd
poll the list for alternative ideas too. FM support is of course
critical - MFM is less of an issue as the host PC can handle that.
I've never built any kind of computer from scratch, so it'll be a useful
experience. I figure on putting just enough code in ROM to support
downloading of actual firmware to the device over whatever the link is
to the PC, as that should save a lot of headache!
Hopefully RAM requirements will be low enough that I can go the SRAM
route and avoid messing around with DRAM refresh (although IIRC the Z80
has much of the necessary stuff built in...)
I think the 8271 is pretty limiting ... I'd vote for a 1793 (or 2793
which has a bulld in data-separator) - it is used in a lot of classic
systems, can handle a wide variety of formats, and can do raw track
reads.
A single 32k SRAM should be plenty to buffer a few tracks, which is
really all you need.
Have you tried just using the diskette controller in a PC? - I've
found that almost all of my P1ish machines can read/write FM, and
I've used ImageDisk to backup and restore almost all of the soft-
sector formats that I have here (although some are better than others.
I've found that Intel mainboards work very well, although the ones
I have only support one drive select).
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.parse.com/~ddunfield/museum/index.html