11 Jun
2010
11 Jun
'10
12:11 p.m.
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.
Eric