02-16-2016, 08:27 AM
(02-15-2016, 09:10 PM)admin Wrote: Each 16 bit value represents the flux duration/25ns. So, you take the value and multiply by 25 to get the total number of nanoseconds that each flux duration lasts. You have to also convert the drive speed to match the original recording speed during your conversion. That value gets converted into a 0 or 1 that is used for the FM encoding. You will notice that your values are either approximately 0x010A or 0x0085. These values are 8us and 4us. You are using a 360 RPM drive to read your disks. This is how you calculate it:
0x010A = 266
266 x 25 = 6650
6650 x 1.2 = 7980ns (7.98us)
1.2 is the value needed to convert a 360RPM value to a 300RPM value.
I know MFM and GCR quite well, but I don't really know much about FM, so you will need to figure out the encoding/decoding requirements.
Thanks! that clears up just about everything. So in essence, there is no "level" of flux intensity, just a duration, where shorter durations represent a "0" and longer durations represent a "1." That would mean all I need to do is build a sequence of 0's and 1's from the flux data, then interpret that binary sequence using whatever encoding scheme is being used (FM, MFM, GCR), correct? I read up on FM encoding and shouldn't have too much of a problem interpreting it. It's just inefficient compared to MFM.
I suppose if I were to plot the flux durations on an x-axis graph, I'd find nearly all of them will end up near one of two points along the axis to give a visual representation of their distribution.