Without proof, it is only anecdotal evidence, of course.  But here is=20
the situation:

I use the Tate programmer (from the 16C84 days) and I modified the code=20
to program chips like the 16F877 when they came out.  The customer got 6=20
free samples of  16F877As in the 44 pin SM package.  I designed a PC=20
board and built 6, using 20MHz ceramic resonators with built-in caps, as=20
I normally do.  The 16F877A programs differently than the 16F877, so I=20
had to modify the algorithm.  The software CLAIMED that the chips=20
programmed OK, but none of them oscillated.  Like you, I had never heard=20
of such a thing happening, so I searched for other causes.

After exhaustive testing without results, I replaced a 20MHz resonator=20
with a 4MHz resonator, and it suddenly worked.  An 8MHz resonator also=20
worked.  But not a 20!  The leads for the resonator were as short as=20
practical, as I have had trouble at 20MHz if the leads are too long.

At the time, that was all the proof I needed.  If you need more, I can=20
always send you a couple of the chips and a copy of the artwork.  I=20
don't think it is worth the effort, and my point is "Be aware that free=20
samples may not be prime parts".

Kerry


Olin Lathrop wrote:
> Kerry Wentworth wrote:
>  =20
>> I had a customer that ordered 6 PICs as samples from MicroChip, and
>> not one of them would oscillate at 20MHz.
>>    =20
>
> Really?  My immediate suspicion is the crystal circuit wasn't properly
> designed.  Too high or low or open load caps, wrong oscillator setting, b=
ad
> layout, etc.  I've done well over 100 PIC projects and have many individu=
al
> units in the field, yet I've never heard of a PIC not oscillating when th=
e
> rest of the circuit and the firmware setup was right.
>
> Unless you can offer some kind of proof it was the PICs, the far more lik=
ely
> reason is that you screwed up, not Microchip.  Extraordinary claims requi=
re
> extraordinary proof.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
>  =20



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