Just a quick thanks to all the suggestions on this.  Turns out that the 
  bypass caps were part of the problem.  Once in, the oscillator started everytime
  just fine.  Turns out that it was occasionally starting before and I believed
  it to be running erratically, but it was fine and the code had incorrect
  timing in it 8-)  Darn PIC was doing exactly what I told it to! 
  Again, thanks for the help.  -James

> 
> Hello James,
> 
> Try to put a small 0.1uF capacitor across Vdd and Vss pins, close to the 
> chip.
> 
> I think this will fix the problem.
> 
> Regards,
> Marcus
> 
> ----- Original Message ----- 
> From: "James Cizek" <jcizek@yuma.acns.colostate.edu>
> To: <piclist@mit.edu>
> Sent: Friday, September 26, 2008 4:12 PM
> Subject: Re: [PIC] Oscillator stability question
> 
> 
> >
> >
> >  I am trying to use this ceramic oscillator:
> > 
> > http://www.mouser.com/Search/ProductDetail.aspx?qs=jVl71O%2frr735X6dB780dCg%3d%3d
> >
> >   I DO have the XT fuse set, and I do have both sets of Vdd and Vss pins 
> > connected
> >  to supply.
> >
> >  Marcel,  you mention a bypass capacitor as close to chip as possible. 
> > Are you
> >  referring to a cap across the supply lines? Or the caps from the crystal 
> > to ground?
> >  I currently don't have any capacitors across the supply line.  (I am 
> > using a lab
> >  quality power supply for testing, but it certainly doesn't mean that the 
> > leads in
> >  aren't picking up noise.... a good point to remember)
> >
> > Bill, you might be right on the crystal, I was told it was parallel cut 
> > when I
> >  purchased, however, I don't have a lot of faith the salesperson actually 
> > knew.
> >
> >  Thanks for the insight.  -James
> >
> >>
> >> James Cizek wrote:
> >>
> >> >
> >> >   Hi folks, new to list but have been searching archives for several 
> >> > days now.
> >> >   I have been using 16F84 pics for a long time. No trouble. Venturing 
> >> > out to
> >> >   the 16F877A chip now and having LOTS of OSC problems. I found several 
> >> > people on
> >> >   list in the archives that seem to say the Murata ZTT-4.00MG ceramic 
> >> > osc works
> >> >   great.  I cannot get mine to start at all.  I gave up and went to a 
> >> > parallel
> >> >   cut 4.00mhz crystal with 27pf caps to ground. All leads are VERY 
> >> > short, and grounding
> >> >   is good.  It will start, but oscillates wildly, one interesting 
> >> > point, if I touch
> >> >   the crystal pins while it's running (with my finger) it seems to 
> >> > settle down and
> >> >   operate close to proper.  I get same results with breadboard OR 
> >> > soldered into
> >> >   circuits. I have tried several different 877's also with same result.
> >> >   I did see that in the datasheet for the 877 they show a resistor 
> >> > marked "RF"
> >> >   in series with the crystal and state that it "may be needed with AT 
> >> > strip cut crystals".
> >> >   Might I need this resistor?  I am not sure if my crystals are strip 
> >> > AT, I was sold
> >> >   them as "parallel cut" and nothing more.
> >> >   Anyone have any insight on my instability with the 877??  Many 
> >> > thanks.  -James
> >> >
> >> >
> >> >
> >> >
> >> Hi James,
> >>
> >> 1. ZTT is a ceramic resonator and they do work great.  I've put 10's of
> >> thousands in the field over the past 16 years on PICs.
> >> 2. Do you have the oscillator config bits set for XT mode?
> >> 3. Do you have a part # on the crystal you are using?  It sounds like it
> >> might be a series cut by its behavior.  Spec sheet says it must be a
> >> parallel cut.
> >>
> >> Personally, the only oscillator troubles I've ever had with any PICs
> >> centered around using an SMD style resonator and that was only a couple
> >> of different manufacturers at the higher frequencies.
> >>
> >> Bill
> >> -- 
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> >>
> >>
> >
> > -- 
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> 
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