On Tue, Aug 03, 2004 at 07:35:50PM -0700, Vince Herman wrote:
> I have been mostly lurking, trying to absorb enough to
> get started.  Here it goes...

Well welcome aboard.

> I purchased a serial programmer from picallw.com
> (P16Pro40), a breadboard, a package of various
> resistors and LEDs.

Good start.

> A few 16F84A and 16F877A samples.

Lose the 16F84A's and get yourself some 16F88 samples. My page here talks about
the advantages, one of which you refer to later on in your post:

http://www.finitesite.com/d3jsys/16F88.html

I just updated it last week.

BTW the 16F877A is cool to work with.

> I have MPLAB installed, I assembled sample code and
> programmed an 877 with an LED blinker sample.  Looking
> at the schematic that came with the code, I see that I
> need to get crystals and caps.

Well it's a bit more complicated than that. You need some way to clock the
PIC. There are several:

1) The aforementioned crystal/caps combo. Essential for any precisely timed
   operation.
2) ceramic resonator. Cheaper. Often comes with built in caps.
3) Crystal osciallor. More expensive but only a 3 wire hookup.
4) Internal oscillator. All Pics with nanowatt technology has them. One reason
   why I like the 16F88. With it, you need no external connections.

5) RC oscillator. You have resistors. You have capacitors. Hmmmmm.

The interesting thing is that there's isn't much of anything out on Google
on the subject. I spent a whole 7 minutes looking! ;-)

The 16F877A datasheet figure 18-8 describes the effects. Try a 100 pF cap and
a 3.3Kohm resistor wired as Figure 14-3 on page 146. Should be good for the
ballpark of 2 Mhz, which will let you do all the testing you need while you
get around to getting resonators or crystals. Resonators are easier to wire
(dur to built in caps) and are cheaper. You only need crystals if you need
very precise timing resolutions.

>  The caps I can get
> form Radio Shack.  The crystals I cannot find.  Where
> do I order them from?

Cheapest overall is Randy at www.glitchbuster.com. Crystals (caps included)
and resonators in the 45 to 60 cent range, with only $1.85 shipping on an
order. Highly recommended.

>
> (sorry for the basic question, I have been reading
> trying to see someone else ask)

Ask away! Most of us love talking about this stuff.

Anyway test it out with your RC circuit until your resonators come it. Be
sure to change the CONFIG line in your program to indicate that you wish
to use the RC option.

BAJ

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