25 Oct
2005
25 Oct
'05
10:04 a.m.
Subject: Looking for an 8 bit FDC...
From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
Date: Tue, 25 Oct 2005 17:28:35 +0100
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>
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...
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.
ick poo.. The 8271 was not widely used especially on 8bitters. If your
serious then 1793 that was common as house flies and does most all soft
formats. Actually with the exception of the GCR and hardsector formats
that one chip is a good start. GCR (apple) is all software and a trivial
amount of hardware (no special chip). Other hard formats have the problem
of being unique to themselves (NS* hard is not like Heath hard) though
it's possible to create copies of each of those as well.
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...)
Seriously 32kbyte static ram chips are easy to get (JDR and other have them)
and EEprom (small is 2k and 8k are easy to find).
Another way to do this is a small S100 bus with 16k of ram, a rom card
Z80 cpu card and a serial board with one each of:
NS* MDSA-4(a common hard sector that one does SD and DD)
Tarbel 1771 based card (SD and really off 1771 specific formats)
CCS 1793 based soft sector card. (most all softsector formats)
Compupro 765 based card (why not!)
In 7 commonly found S100 cards you cover 90+% of all floppies.
The rest is software.
If you stick to static parts and 6502 or Z80 the whole thing should be
simple. Parallel port (bidirectional) will be faster but serial is easier
though slower.
Allison