Bob Ammerman wrote:
> Note: Don't expect too much accuracy out of your
> run-of-the-mill crystal based oscillator. You will get
> significant drift over time, temperature, and I believe
> supply voltage.

"...and I believe supply voltage" - Bob, two weeks ago
I've received few PIC16F871 from local Microchip folks
(www.microchip.com.ua) . Also received crystals from
them for these PICs. Crystals were 20 MHz without any
additional information.
   If I were Olin, I'd rather just stick them to these PICs. :-)
Look at his posting:
"Re: [PIC]: Serial resistor for the oscillator of a PIC16F876"
on 2002-07-09 :
   > > The point is that I need to know some suitable value
   > > for the serial RESISTOR
   >  I always use 0Ohms.  Where did you get the idea from
   >  to put a resistor there anyway?  I don't recall ever seeing
   >  a resistor in any Microchip documentation.

   But I asked local Microchip folks about crystals'
parameters. They sent me datasheet from witch I've
found out that crystals were

Jauch Quartz HC49/U4H SS4 0.1 mW max drive level!

From Microchip AN826 Crystal Oscillator Basics:
Power dissipation of the crystal can be computed by

P = E^2 / R1 where E is rms voltage across the crystal.

R1 is known to be about max 100 Ohm at 20 Mhz.

So aprox max P would be 2v^2 / 2 / 100 Ohm = 20 mW.

Too much for 0.1 mW max drive level crystal.

Of course, "You will get significant drift over time..." :-)

...........................

Mike.
Correct me if I'm wrong, please.

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