amiga floppy disk reading experience
eric at brouhaha.com
Fri Jun 11 14:11:58 CDT 2010
Chuck Guzis wrote:
> Take a look at some of the old Western Digitial FDC app notes,
> particularly those for the 179x controllers for ideas on how data
> separators can be implemented.
Note that the only data separator worth a damn in the WDC app note are
the two that use PLLs. The most commonly used was the one in Figure 14
that uses a 74LS629 VCO and the phase comparator of the WD1691. The
circuit by MPI in Figure 13 that uses an MC4024 VCO looks OK but I
haven't seen it used. The rest are crap.
Figure 11 uses a one-shot, and won't work reliably even for single
density. It's comparable to the worthless data separator built into the
1771. Figure 12 uses a state machine and works approximately the same
way the Apple II read state machine works. It's probably good enough
for single density, but won't work reliably for double density.
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