Disc reader project -- quick status update
cclist at sydex.com
Wed Dec 9 14:55:35 CST 2009
On 9 Dec 2009 at 11:35, Al Kossow wrote:
> You probably have more experience with odd formats and using the
> Catweasel. Is there anything you've run into that couldn't be dealt
> with using the sample rates on that board? Did you ever experiment
> with the sampling rates on double-density data?
I've never run into anything that could be classified as "vintage"
(>20 years old) that couldn't be handled with the original ISA Mk I
board (I do have a MK 3 and a MK 4, but they almost never get used).
The clock rates on the CW are somewhat limited, so I haven't done
much there. Generally, I aim for the shortest interval between
transitions to be about 10-20 clocks, which seems to give adequate
I wonder if there's anything to be gained by using a sample clock
that's a power-of-two multiple of the data rate. It could be argued
that dividing an MFM bit cell into 7 sample intervals rather than 8
would lead to a more accurate center-of-cell reading. My current
project uses a 14.3MHz clock instead of a 16. I'll know more when I
get it running.
The saving grace in all of this floppy business is that, unlike hard
drives, the push was to make floppies physically smaller, while
keeping more-or-less the same capacity. If the same product
development had been followed using hard drives, we might be looking
at 30MB hard drives the size of the head of a pin...
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