> > To get an "exact but average" 60Hz with a 20MHz isn't too difficult
> > but there are easier ways
>
> True, but just using the closest divisor from the 5MHz instruction
> clock is still far more accurate and stable than a 555 timer.

I know - I've just refurbished someone's circuit built 10 years ago
that used  555s and 4020s as a serious attempt at a stable and
accurate 1/4s time-base. Needless to say, even if you can set the
frequency in the first place, which the user had great difficulty doing,
especially in the field, it drifts and has adjustment pots all over the
place. And it's not as smart as a PIC either

I didn't realise what the end-use of the circuit was. I asssumed the
coincidental 60Hz was some mains-power simulation

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