Looking for an 8 bit FDC...

[Jules Richardson]

Chuck Guzis wrote:
> If what you're really after is a "read anything" system for archival
> purposes, why bother with someone's FDC?

Well I don't really need 'read anything' at this stage - handling fairly 
  stock FM disks (of various sizes) would be a good place to start...

> That was then and this is now.  If you can find a 64KB FIFO (salvaged from
> an old video card maybe) or a bunch of 8 bit counters and some SRAM, you
> can build your own version of a Catweasel and read just about
> anything--including those Victor 9000 or Motorola VersaDOS diskette or any
> number of bizarre copy-protection schemes.  You can use an 8255 for drive
> control and the rest is mostly LSTTL glue.    Writing is a  little more
> complicated, but reading is simple.

Yep, that's my ultimate aim I suppose - I know I've mentioned it on the 
list before and bounced circuit ideas around with a few people. I just 
fancy trying a simpler approach first :)

My plan was 8 bit counters and SRAM - with the latter salvaged from old 
PC cache memory, with something like 8x oversampling and buffering at 
the track level - then doing all the processing in software.

I *think* in my scribblings (which I don't have here) it required 128KB 
of SRAM, which isn't impossible - it's just a little more complex to get 
something up and running than the SBC with FDC approach.


Right now I'm leaning toward starting out using a stripped-down BBC 
micro with 1770 FDC as a development platform as it gives me all the 
necessary serial / FDC / memory circuitry and I can develop necessary 
code a little easier than doing it blind with a homebrew board. Later on 
I can simplify the BBC's circuitry a lot and put everything onto a 
homebrew board.

But yes, ultimately I'd like something that read raw track data and 
could hopefully allow analysis/recovery from disk errors as well as 
supporting a lot more formats...

cheers

Jules