>I have a design which we are having occasional in-field lockup issues
> with...  I'm still troubleshooting and trying to reproduce (and cure) on
> the bench.
>
> The specs of relevance:  3.3V supply, PIC18f26K20, 47K external pulling
> MCLR high.
>
> Tonight I had a locked-up unit.  Curious if a reset by putting MCLR low
> would resolve the issue, I hooked a jumper to the MCLR end of the 47K
> resistor - and amazingly (without anything attached to the other end,
> the unit reset).

We had problems with the 18f45k20 locking up after being switched on.
It needed some series resistance into Vdd to limit the rise time.

I looked in the 18f26k20 errata sheet for revisions A4 and A5 (80379A) and=
=20
found the same fault (section 18):

"The part may hang in the Reset state when VDD
falls to the POR rearm threshold of approximately
1.2 volts then rises at a rate faster than 7500 volts
per second to the operating range. Recovery from
the hung state is possible only by first lowering
VDD to below the POR rearm threshold followed by
raising VDD to the operating range."

If you happen to be using that silicon revision this might be related.

James
The part may hang in the Reset state when VDD falls to the POR rearm=20
threshold of approximately 1.2 volts then rises at a rate faster than 7500=
=20
volts per second to the operating range. Recovery from the hung state is=20
possible only by first lowering VDD to below the POR rearm threshold=20
followed by raising VDD to the operating range.

--=20
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