Re: Using a PIC as a floppy disk controller

"Homer J Simpson" <nobody@xxxxxxxxxxx> wrote in message
news:KyoNg.3714$bf5.1529@xxxxxxxxxxx
I do recall that the Woz built his controller out of TTL, though in an
ingenious way. Still his clock rate was way below a PIC chips' abilities.

That's pretty much what I was suggesting with the "small CPLD" approach. You
can get, e.g., 64 macrocell CPLDs that aren't much bigger than the size of
your little fingernail, and stuff as much logic into them as a couple dozen
discrete "jellybean" logic ICs (
Granted, Joerg might be able to do it more cheaply using jellybean logic...
:-) ). The "fast" part is sampling at a MHz or so to find the clock and data
bits, synchronizing to them, and then bundling up the data into, e.g., an 8
bit latched output that a PIC could read.

Back around 2003 I provided a modicum of assistance getting the Commodore One
(http://c64upgra.de/c-one/) floppy interface going. She was using large
Altera FPGAs, and the floppy interface did end up as some pretty small "fast"
logic cells with the 6502 core having all the file system smarts. Hence if
you're up for doing a larger FPGA design, there are free microcontroller cores
on, e.g., freecores.org -- I believe some are even PIC compatible.

---Joel



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