25 Oct
2005
25 Oct
'05
5:18 p.m.
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