> Basic PIC like the 16F84.. I have a few free ones I got from
> MicroChip, some of which I think will work. 
> 
> 16LF819
> 18F252
> 18F452
> 16F630

Well, you'd hope they all work ;-) Not a good look is it, starting
a new hobby with duff chips

The F84 works fine, although it has only simple I/O. It's one of
Microchip's earliest micros and there's a lot of code out there
for it. If you already have some, by all means use them, but they
are more expensive than the replacements (F628, F88 etc, check
the line card) and you can do better performance-wise for a lower
price if you're buying micros in the future

Even the 18Fx52 are getting a little old too now but are a good
introductory micro and still commonly available. All of the above
can do everything the F84 can do and more

As for your registry problem with MPLAB, I've never struck
that either. Sounds very odd

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