Looking for an 8 bit FDC... - test-drb@ccmp.vtda.org

25 Oct 2005

...

Subject: Re: Looking for an 8 bit FDC...
   From: Jules Richardson <julesrichardsonuk at yahoo.co.uk>
   Date: Tue, 25 Oct 2005 18:43:13 +0100
     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>

Allison wrote:
  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.   
Ahh, not had experience of that one before (I don't think anyway). 177x 
was pretty common in machines over here, and the 8271 gets used in a lot 
of Acorn hardware which is why I'm used to it... 
the Acorn is one of the few that used it.  The 8271 was rare here compared 
to 1771 and 1793.

...
   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). 
Well part of the plan is to raid the junk pile and at least put some of 
it to use, which would likely mean a 2732 EPROM for on-board ROM and 
6116 SRAM chips for memory - latter subject to power requirements and 
board space though. I know I've got quite a few of them kicking around, 
but they're physically large chips and not *that* big a capacity (8kbit 
or 16kbit I think, going from my hazy memory...) 
The 6116 is a great part and 4 of them are enough for a track level buffer
and another 2 would provide adaquate code space.

...
 Of course I've got a boatload of various DRAM chips
though, so if the 
Z80 does provide pretty much all the refresh needed then maybe that's a 
better bet. 
GO TO Gaby's site and look for Tim Olmstead DRAM article.  It covers DRAM
interface in the context of Z80 systems and is very complete.

...
   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!)

Ahh, thanks for that list. We've got a truckload of S100 hardware at the 
museum, so there's definitely a possibility there - I'm just not sure 
without checking what FDC cards we have. I don't know what spare ROM 
boards we'll have either (my programmer won't do three-rail devices, so 
I'd need a board that'd take slightly newer EPROMs...) 
Or enough eprom to boot over wire.  Everytime I need a system to do xxzzy
I find enough peices in the S100 spares bin to build it with minimal fuss.

Simple enough, anything with WD1771 will do SD, 1791/93 does SD and DD
and there were some cards with 765 (Compupro) that do SD/DD. 
The real key is documentation, however for the popular cards its wasy to
docs on line.

...
   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. 
Agreed :) I can't see parallel being complex though; I guess there's 
just handshaking protocol to design on top of hooking the chip itself up 
(unless I got for individual ICs to do the parallel interface), but it 
doesn't need to be anything complicated. 
It's really traffic management, who talks first and when. ;)

...
 I've got a few weeks until I'm back in the UK,
so it gives me something 
to ponder over in the meantime though :) 

Good luck,
Allison