John J. McDonough wrote :

> OK, from your description, sounds like is should work ... but

It does not, AFAIK.


> 1) Check your circuit - again.  And then again.  Do you have power and
> ground on the correct pins?  I know this sounds stupid, but 
> when you are
> fixated on the crystal, it can be pretty easy to overlook 
> obvious problems
> elsewhere.
> 
> 2) How confident are you in your scope?  You are using a 10X 
> probe, correct?
> You don't want to be loading down the circuit with the scope. 
>  The trace
> does at least do a little dance when you touch the circuit, 
> right?  You did
> remember to switch the channel to AC coupled and not GND.  
> (Sorry, I got to
> ask all the things that have nailed me!)
> 
> 3) Take a high impedance meter and measure the voltages to 
> ground from both
> sides of the crystal.  They should be above zero but not Vdd.
> 
> 4) Check Vdd and !MCLR at the PIC.  Vdd should be Vdd, and 
> !MCLR should be
> close.
> 
> 5) AFTER trying all of the above, lift the caps and try 
> again. 99% of the
> time the PIC will oscillate with just the crystal.  If the 
> caps are shorted
> or too large the PIC won't oscillate.
> 
> 6) Remove the power and the PIC.  Measure the resistance from 
> each of the
> pins to ground.  If any are too low, you could be simply 
> sucking the life
> out of the PIC with your external circuit.
> 
> 7) Try a different crystal.  Crystals are pretty easy to 
> toast with the
> slobbering iron, and very sensitive to shock.  I know, quartz 
> should be
> impervious to heat, but it's a tiny piece of quartz and like 
> glass, a rapid
> temperature change can crack it.  Hot solder on one pin is 
> going to make a
> lot of thermal stress.  These things are way more fragile than the PIC
> itself.
> 
> You don't need an oscillator to program the PIC.

No, **BUT**, you need to program the PIC to use the oscillator.
(An un-programmed or erased chip used the RC osc. And I can't
see why the crystal osc should be enabled/running in that case...)

I'll start with that, *then* check your steps 1-7 above...

Regards,
Jan-Erik.

> Assuming 
> you are using in
> circuit programming, 4 and 6 could also prevent you from 
> programming the
> part.
> 
> hope this helps
> 
> --McD
> 



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