Thanks guys!  This and Bob's feedback are what I was
looking for.  It's not hard to "read the datasheet",
but unfortunately, the datasheets for any chip list
what it's rated to do.  While you *should* stay within
these limits, I was wondering what experience you guys
have had actually using it.

On a side note, the 4017 is only rated to source about
10mA per output (if I recall correctly), but I've
built a circuit which drives 20mA per output ... built
the same circuit at least a couple of dozen times, and
never had any problems.  Again, this may not be
"optimal" design practices - but I'm not
mass-marketing anything, or putting it into a
life-and-death type of circuit.  Thanks for the
feedback and experience.   :)

ATM

--- "Gennette, Bruce" <bruce.gennette@TAFE.NSW.EDU.AU>
wrote:
> About RA4 - Open-collector Output, Schmitt trigger
> Input
>
> 1 - It can't source *ANYTHING*  itself
> 2 - It can sink quite a bit, and it has in-built
> protection diodes to drain
> off excess voltage (at the level you would use).
>
> As you have suggested the solution for your problem
> is to make the pin an
> output and 'pull up' its output with a resistor from
> +9V.
> The +9V either goes to the 4017 when the PIC +5V
> output is Hi, or is pulled
> into RA4 when it is Lo (thus providing a level
> shifted output, exactly what
> RA4 was designed to do).
>
> If it doesn't reliably clock then add a 1K between
> the 4017 and the pull up
> so that the PIC will always win a struggle to sink
> the voltage.
>
> You should design for a minimum 1mA @ 9V to trigger
> the 4017, so from R=V/I
> = 9/0.001 = 9K, use 4K7 for a 'more than strong
> enough' signal.
>
> Bye.


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