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cr1901
February 26th, 2015, 03:31 PM
Recenty, I've been trying to find documents which describe how a floppy drive and controller work together to get data from floppy surface to the CPU. From previous searches, I know that the process is relatively involved. However, I know documents exist that explain the various representations that the voltage signal goes through (including the MFM encoding, data windows, clock recovery, sync marks that violate MFM encoding, and the actual control data format as stored on disk), from floppy surface to PC. They are meant for controller designers, but as someone not likely to make an FPGA version anytime soon :P, I still see utility in reading them to get a good grasp on the limitations/features of the 765 (i.e. why copy protection works, why higher density floppies and their drives need a different controller, etc). One particular copy of the NEC 765 datasheet, which I've been unable to find in the past two months, recommends reading NEC Application Notes 8 and 10 to get a full description of how a floppy disk, floppy drive, and controller work together to extract data.

Thankfully, NEC Application Note 8 is on archive.org (https://archive.org/stream/bitsavers_necdatashe79_1461697/uPD765_App_Note_Mar79_djvu.txt), and having not fully read it yet, that document is probably enough to satisfy my curiosities as described above. However, just in case... does anyone who worked with floppy controllers in the late 70's/early 80's have a copy of Ap Note 10. I'm going solely off my browser history- indeed, I did a search for "NEC Ap Note 10" two months ago, but I can't find the source which recommends reading that document in the first place :P. I just recall that it is a complement to the 765 datasheet/Ap Note 8.

Well, at least one document which describes floppy physics and circuitry is archived for years to come. It may be for only one type of floppy as specified by IBM, but it's a start.

Chuck(G)
February 26th, 2015, 05:11 PM
You'd be best off by starting at the beginning. Try the Shugart SA-800 Theory of Operation (http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/shugart/SA8xx/50664-0_SA800_801_Theory_of_Operations_Apr76.pdf) for the low-down on floppy drives.

Then, check out the a bit on double-density recording (http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/shugart/_appNotes/SA800_Series_Double-Density_Design_Guide_1977.pdf)

Take a peek at the Western Digital archive on bitsavers for controller information. The 179x app note is useful for showing how the drive is interfaced. (http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/westernDigital/FD179X_Application_Notes_Jun80.pdf)