02-17-2016, 01:43 PM
(02-16-2016, 02:49 PM)admin Wrote: Please note, that I made a typo in my post. You have to ignore every other bit (the clock bit) when doing the decode to standard data!
Ah, yes. bit vs. byte certainly makes a difference.
The confusing part for me is the base timing, which I recently learned is in units called "bit cells." I had no idea what to do with the flux durations other than relate then to themselves and not to another base standard. After looking at an SCP file of an MFM DOS disk in the HxC visual viewer did I notice that application putting tick marks at regular intervals in and around "spikes" which I believe indicate flux transitions. After reading academic papers on the subject did I learn of the term bit cell, and that's what HxC is outlining with those tick marks. But, I still needed to know the length of a bit cell so I can correlate the SCP flux durations with the bit cells needed to decode MFM. I finally found this resource, ftp://ftp.eskimo.com/home/mzenier/cd-8002-1.pdf which explains that a bit cell is 2us wide for MFM and 4us wide for FM.
Now, I may be completely overlooking some obvious fact otherwise, which is not uncommon for me sometimes, but the above knowledge has helped me to understand the encoding scheme. It makes sense to me, but I haven't tested the theory yet. I posted it here in case it helps others, too.