Looking for an 8 bit FDC...

[Jules Richardson]

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...

> GCR (apple) is all software and a trivial
> amount of hardware (no special chip). 

I'm  not hugely worried about GCR formats (I gather the ACT Sirius uses 
GCR too) at this stage, although I suppose if it's just reasonably 
simple logic then I can keep in mind - ability to add the relevant 
daughtercard to this planned board at a later date, say.

> 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 not given thought to hard sectored disks at the moment - I'd expect 
that the common FDC chips don't support them at all, so it's a different 
  project entirely...

>>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).

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...)

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.

> 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...)

> 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.

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 :)

cheers

Jules