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'Pic Osc Problems'
1997\07\09@033554 by Robert Drake

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HI All
       Has anyone else had problems with pics and oscillators? we can
not get the levels on the OSC1 and OSC2 pins to a sufficently good level
the mchip data book says 0.7xVDD however getting this takes a large
ammount of time and playing arround. We found that for a 71/54C @500k
the best values were 150p(osc2) and 100p(osc1) but then the load
capacitance is unmatched and the waveform on osc1 is distorted. Has
anyone done any work on getting the best out of resonators(murata are
the ones we use). We use 500k 2M and 4M, with each increase in value it
is becoming harder to get 0.7VDD any ideas/ recomendations.
       Sory to go on about it but anyone seen the ATMEL AVR simulator
yet... they put in a command line like the old MPSIM for DOS, Horray :-)

       Robert Drake - Development Engineer EMS

1997\07\09@132322 by Harold Hallikainen

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On Wed, 9 Jul 1997 08:05:28 +0100 Robert Drake <spam_OUTrobertTakeThisOuTspamEMS1.DEMON.CO.UK>
writes:
>HI All
>        Has anyone else had problems with pics and oscillators? we can
>not get the levels on the OSC1 and OSC2 pins to a sufficently good
>level
>the mchip data book says 0.7xVDD however getting this takes a large
>ammount of time and playing arround. We found that for a 71/54C @500k
>the best values were 150p(osc2) and 100p(osc1) but then the load
>capacitance is unmatched and the waveform on osc1 is distorted. Has
>anyone done any work on getting the best out of resonators(murata are
>the ones we use). We use 500k 2M and 4M, with each increase in value
>it
>is becoming harder to get 0.7VDD any ideas/ recomendations.


       We are using muRata resonators with built-in capacitors at 16
MHz.  They have worked well for us.  We originally tried some from ECS
and from Integrity Technology.  Both worked well in the prototypes but
failed in production.  We were getting about a 50% failure rate.  We have
not had any of the muRata's not work.  We talked with ECS, Integrity and
muRata.  Also talked with Microchip about getting a good model of the
oscillator (on the 16C74A) (graphs of input Z, output Z, gain and phase
vs frequency) so we could pass that on to the resonator companies.
Microchip did not have that info available.  They pointed out that their
oscillator documentation isn't worse than anyone else's (true...).
murata said they were working with Microchip in Japan to characterize
resonators for use with the mMicrochip chips.
       For now, we're using muRata with built in capacitors!

Harold

1997\07\10@072912 by all (Stephen Birchall)

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we tend to use 4meg ceramics a lot  and tho' we get them from various
suppliers, find about 10 per cent or so won't work. (on any pic)





{Quote hidden}

1997\07\10@114333 by Reginald Neale

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>we tend to use 4meg ceramics a lot  and tho' we get them from various
>suppliers, find about 10 per cent or so won't work. (on any pic)

We use a Panasonic 2 MHz with built-in caps (PX200) with a 16C54. We've
built tens of thousands with no statistically significant resonator
failures.

Reg Neale

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