Disc reader project -- quick status update

[Chuck Guzis]

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 
results.

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...

--Chuck