At 04:19 AM 2/23/00 +1100, you wrote:
>Dan Michaels wrote:
>
>> Secondly, I've found, much to my chagrin (meaning $$$ wasted),
>> that you don't want to tie a capacitor straight onto MCLR on a PIC,
>> as this can damage the chip and lead to very large leakage
>> currents into the MCLR line (order of 100s of uA).
>
>  What I think you mean is that a large cap on MCLR pulls it well above
>Vcc when Vcc is shut off and that may cause strange behaviour.
>--
>  Cheers,
>        Paul B.
>

Paul,

Right. My take on it is, when you shutdown the system, Vcc goes
down fast and the cap discharges into MCLR, damaging internal
circuitry, probably the programming (rather than reset) stuff.

The chips are clearly damaged, as evidenced by large *quiescent*
leakage currents into MCLR, subsequently (cap or no cap). How/why
this causes flaky/hit-or-miss program execution, I have no idea.

Because of this susceptibility, I now use lower pullup R's (1-5K,
formerly used 20-50K), and NEVER tie any caps on MCLR.

- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
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