Looking for an 8 bit FDC...

[Dave Dunfield]

>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