On 28 Mar 2017 at 11:21, James Wages wrote:

> Brent,
>=20
> Specifically, have a look at the rightmost column of text on page 2-4 of =
the following PDF:
>=20
> http://ww1.microchip.com/downloads/en/DeviceDoc/01146B_chapter%202.pdf
>=20
> QUOTE: "...especially useful in cases where the pull-up can be
> increased to a very high resistance such as 100k or 1M."=20
>=20
> Hmmm...  What "cases" would those be?

....cases where power consumption would be compromised if lower values were=
=20
used, and cases where noise immunity concerns are less of a problem.

In the specific case of MCLR though, it can often be that the pin has a pul=
l-up tied to=20
it and connects to a programming header and nothing else... so long as it f=
loats it=20
essentially consumes no power most of the time, regardless of the value of =
the=20
resistor.
=20
> I myself have been using 100k pull-ups with a Vcc=3D3.0V on a
> PIC16F1508 without problem, but I've not yet tried 1M? pull-ups.  I
> would think 1M? pullups would cause noise issues, even if they do
> work.

If all your PIC circuits are bread-board or other "in the lab" type applica=
tions, then=20
yes they may well workd acceptably. But somewhere else like say an industri=
al=20
environment, then yes you are correct - expect noise issues.

> But if it is possible to use such high values for pull-ups,
> that means the internal impedance of the PIC's digital I/O input
> pins would have to be much higher than 1M=A9, possibly on order of 10
> times higher.  But is the internal impedance of a m?dern PIC's
> digital I/O input? really on order for 10M=A9 or higher?=20

Yes, really. Why shouldn't it be?



--=20
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