John Pearson wrote:
>
> I am interested in Mike Harrisons idea of trying to get an mpu reset
> circuit (chip) to oscilate, using some resistors and a cap, for my low
> speed external mpu clock.
>
> I need 100Hz nominal, but higher (200, 300) would be okay.
>
> Unfortunatley, I am not really good enough in analog to implement this.
> Could anyone give me some guidelines or some ideas to get started. I have
> studied some comparator oscilators but not really sure what I am doing.
>
> Thanks for any help.
>
> John


Why not just use the RC clock with a big C??

From what I know of the RC clock driver from the datasheet,
looks like the standard C charged through R and discharged
by the open-drain fet in the PIC when the voltage reaches
the threshold. Just like a 555 timer etc. I can't see any
reason you couldn't just use a 100uF cap and have a 1Hz
clock speed if you like, and 100Hz should be fine too.

You MAY need a series R in the OSC1 circuit to reduce
discharge current but I am not sure if the PIC does this
itself anyway. All guesswork really! :o)
-Roman

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