Olin,

   In another words, weak pullup saves power since it
does not require that much current to move between the
states since MOSFET required voltage and not current
thanks to it's high impedence? Should we just design
preferable around weak pullup pins for I/O?

Thanks
John

--- Olin Lathrop <olin_piclist@embedinc.com> wrote:

> Robert Rolf wrote:
> > So they fabricate a current source that gets
> turned on to enable
> > 'weak pullup'.
> 
> I don't think so.  Most likely it's just a P channel
> high side FET
> deliberately made small to have a high on
> resistance.  In that case it looks
> more like a resistor than a current source.
> 
> The main distinction of "weak" is that its current
> is intended to be small
> enough to be within the normal sink capability of
> external components
> driving the pin.  The pullup is also designed to
> tolerate the output
> externally held low indefinitely, which is something
> the standard strong
> pullup is not rated for.
> 
> 
>
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