On 10 May 2009 at 23:21, Andrew Lynch wrote:
Hi! I sent this message earlier but it seems to have
gotten drowned
in all the unpleasantness. Hopefully we can move on to something more
constructive. If anyone would like to discuss disk archiving legacy
formats with an existing low cost home brew Z80 CP/M SBC and Disk IO
board I think the N8VEM project would make a great starting point.
It does everything described by Jules and is common enough now to have
a decent support base. There are at least one hundred N8VEM SBC
owners so that might be helpful in using it to archive disks. It uses
a standard Intel 8272/NEC 765A FDC with some extensions for use with
formats other than the usual 5.25"/3.5" DSDD/DSHD. Especially when
paired with an IDE CF adapter I think it would be a very useful tool.
By "extensions" what do you mean, Andrew? Will it archive Victor
9000 diskettes?
--Chuck
-----REPLY-----
Hi Chuck! Thanks! By extensions, I mean the Disk IO has a regular Shugart
mini-disk interface with all the usual signals and options. It also has the
"feature" interface which imports/exports the rest of the NEC765/i8272
signals necessary for 8" and other drive support. An 8" drive cable with
what signals are needed for that drive could be fabricated using the Shugart
mini-disk interface plus whatever signals/options are needed from the
feature connector. The 8" drive cable would be custom to Disk IO and that
drive but there are multiple 8" drive interfaces so that seemed to me to be
the most flexible way to provide support in a limited PCB space format.
Please check out the Disk IO schematic on the N8VEM wiki for illustration of
what I mean.
http://n8vem-sbc.pbworks.com/browse/#view=ViewFolder¶m=Disk%2520IO
The Disk IO also brings to the feature connector intermediate signals for
external processing like RAWREAD, /INDEX, the decoded FM/MFM stream from the
FDC9229, etc. It also has VCC and GND for easy extension into "smart
cables" to allow external processing of the intermediate signals. A uC or
PC interface could tap off the RAWREAD and /INDEX signals and decode the
disk directly or use the FDC9229 data separator to decode FM/MFM data. I
think hard sector disks could be supported using this technique and even
more exotic formats such as M2FM, etc.
I don't know if the N8VEM SBC + Disk IO board could decode a Victor 9000
disk as I don't know anything about the format. However, with the Shugart
mini-disk interface and the feature connector by themselves it may be
possible. It's very likely (IMO) by using the intermediate signals fed to
an external uC or PC for high speed sampling/decoding using the Z80/i8272 as
a mode controller. I am not suggesting the plain 4MHz or 8MHz Z80 has
enough bandwidth to decode raw read disk flux transitions like a Catweasel
does.
What I am suggesting is if someone were interested in pursuing such a serial
port based floppy disk archiving project is to use the N8VEM SBC and Disk IO
as a starting point since much of the work has already been done. Starting
over from scratch would add a lot of unnecessary work and probably some
marginal benefit when done, if it lasts that long. Using the N8VEM SBC and
Disk IO board the project could launch in days or weeks rather than months
with a "clean sheet" design. If the really exotic stuff were desired which
required a uC or PC interface that could still leverage the existing N8VEM
design as infrastructure and focus on just the disk sampler/decoder using
signals and power supplied from the Disk IO board.
I hope this helps! Thanks and have a nice day!
Andrew Lynch