> The PIC datasheet for the 16F8X parts (DS30430c, pg. 40),
> in figure 8-4, shows "clock from ext. system" going through
> an inverter before connecting to OSC1.  What's the purpose
> of this inverter?

If it's an ordinary inverter and the clock signal you intend to
inject is "clean", then that inverter doesn't seem to serve any
beneficial purpose

If you look ahead to the circuits (8-5 and 8-6) for External crystal
oscillators, you'll see that an 74AS04 is used. One gate of this
hex IC is to tidy up the wave before it enters the PIC. The 04 is
not a Schmitt trigger IC. I think you need gates that can be biased
into their linear region to oscillate with a crystal, and Schmitts
are unsuitable

8-7 shows that there's a Schmitt gate inside the PIC itself, so
if you're confident that the oscillator module has at least an OK
wave (and it probably does), I wouldn't worry about adding an
external inverter

The F628 has similar diagrams but shows no ST inside the
PIC, just an ordinary inverter. I'm sure in both F84 and F628
manuals they intended to advise that Schmitts are used

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