Drew Vassallo wrote:
>
> >What about those PICs with built-in 4 MHz RC oscillators?  How does one
> >qualify a project built with, for example, a 12c508 and not much else.
>
> The FCC requires that the operating frequency of the "circuit" be less than
> 1.7xx MHz to be exempt, I think.  Doesn't matter if it's integrated or not.
> At least that's how it struck me when I read it.


At first glance it might seem that a 12c508 running
at 4MHz (internal RC osc) is really running at 1MHz,
and the highest freq that can appear external to it is
1MHz. But this is not the case as the internals of
the PIC are very much driven at 4MHz, with different
processes operating on each 4MHz clock pulse. The
decoupling capacitor will be buffering current pulses
at 4MHz and the majority of the radiated energy will
be at 4MHz. :o)

Of course, for the cost of one R and one C you could
simply run the PIC at 1.5MHz with an external RC osc.
-Roman

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