I'm using a 16F84, so you guessed it ... I'm talking
about RA4.  It's the only unused pin I have for a
project, and I'm wanting to clock a decade counter
4017 with it.  I know it can't source much, so I want
it to sink current (trigger the counter on a negative
going pulse).  Anyway, the question is:

The PIC runs on 5V, while the 4017 runs on 9V.  If I
tie the clock input of the 4017 to 9V through a 4.7k
or 10k resistor, and use the PIN input to pull it low
(tied between the resistor and 4017 input), will this
hurt the PIC?  I know it would be sinking current, and
it would be low, which is OK.  But will putting 9V
into the open-collector output cause problems?  I'd
like to see if anyone knows from experience before I
kill a good chip.  :)   If this won't work, does
anyone have any other low-parts count alternatives?

Thanks,

ATM

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