Rick wrote:
>You haven't looked hard enough. Just about every CMOS clock circuit I've seen
>has a feedback resistor across its input/output typically 1 meg to 10 meg.
>This
>ensures a reliable startup. The PIC16f is a CMOS device with a high input
>impedance pin and a low output impedance pin (typical of CMOS clock
>generators). The data sheet for the 75T202 chip recommends a 10 meg resistor.

What Olin is saying is that Microchip don't mention it do they?
I would not say a 16F628 oscillator is the same as a standard CMOS clock
circuit.

>The Basic Micro http://www.basicmicro.com/  MBasic manual page 146
>recommends a
>10 meg resistor across the 16f628 using a resonator. The Motorola CMOS
>handbook
>is infested with clock circuits with this feedback resistor. I have designed
>equipment with CMOS logic in commercial/broadcast circuits that use this
>resistor. VDO specifies this resistor in their automotive applications in
>their
>instrument clusters. The Piccon at http://www.qsl.net/n6bg/piccon/ shows a 1
>meg across the xtal. The Simon Bus radio alert receiver uses a PIC, 4mhz xtal
>with a 10 meg across its clock. I could go on and on.....
>Rick

Are any of these examples what Microchip suggest?
I'd say some designers add the resistor out of habit with other micro's.

>Olin Lathrop wrote:
>
> > > Try a 1 to 10 meg resistor across the osc pins. I think I saw a datasheet
> > > somewhere with this requirement.
> >
> > I haven't.  Care to provide a reference?

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