On Fri, Aug 27, 1999 at 07:27:43PM -0700, Anne Ogborn wrote:
>
> How do I tie pin 1 to the crystal?  Just tie it to OSC1 or OSC2?

I think that, on the PIC, OSC1 is nominally the input,
while OSC2 is nominally the output. However, I don't think
(watch everyone else say different) that it's recommended
that you use those as a clock source for other chips if
you're using the built-in oscillator with an external
crystal; I'm not sure that the PIC's oscillator has
sufficient drive for that (I know that it's been discussed
before, but it may come down to one of those questions
where the answer depends on how much of a problem it
would be for you if it didn't...)  If you forgo the PIC's
oscillator and make your own (mostly you need some more
resistors and an inverting buffer like the 74x04), then
the inverting buffer will have plenty of oomph to drive
both the PIC and other devices. uChip shows how to do this
in most data sheets, e.g. Figure 13-6 in the PIC16C6X
sheet. Where it says "To Other Devices", that's where
you'd pick up the signal to feed the 4024. Alternatively,
I suppose you could simply feed the 74x04 output straight
into the 4024, drive the PIC off pin 12 of the 4024 and the
ISD off pin 11.

BTW, the 4024 is also available in HCT; uChip shows
using an AS device feeding CLKIN... does it matter
if the CLKIN is fed CMOS or TTL levels?

--Bob

--
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Bob Drzyzgula                             It's not a problem
bob@drzyzgula.org                until something bad happens
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