Looking for an 8 bit FDC...

Allison ajp166 at bellatlantic.net
Tue Oct 25 13:09:55 CDT 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 
>>>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,

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