piclist 2000\06\09\110726a >
Thread: XTAL startup issues on PIC 73B
www.piclist.com/techref/microchip/time.htm?key=xtal
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face BY : Don B. Roadman email (remove spam text)



On 9 Jun 2000, at 14:29, D. Schouten wrote:

{Quote hidden}

I'm posting this reluctantly because it is not a solution. Some
others had some good Ideas, and I thought I'd submit this little
piece of info for what its worth. I was playing with some 16F84s. I
had a 10 Mhz part that I bought back in 98, I believe, and had been
using it with some 8.7Mhz crystals that came in a grab bag from
Dan's. I tried a bunch of them and they all worked fine with this 10
Mhz pic. About a month ago, I yanked this pic to use temporarily
untill some new ones came.  The vendor screwed up and sent 4
Mhz parts, and I tried them anyway using the 8.7M crystals. None
of them worked and I tried several crystals, so I figured that pics
arent capable of much overclocking. They did work with some 4.7
Mhz crystals.

Just recently, I got very bored and hooked up a 10 Mhz crystal to
one of these 4 Mhz pics, and it ran fine with a simple little led
flashing program. I was amazed, so I stuck a 20 mhz crystal on,
and it still worked! I tried several of both 10 and 20 Mhz crystals
and it always worked. Also tried 3 or 4 of the pics, and always, it
worked. I didnt have any higher freq. crystals to try, so I still dont
know where these chipc would crap out. I didn't have the presence
of mind to examine the oscillator ouput with a hi impedance probe,
so I dont know if the osc wasnt running or the chip crapped out.
Now I suspect the oscillator didnt start. I  surmise that there are
some crystals that some pics just don't like, but I don't know why,
and I guess I never will short of doing fully instrumented detective
work.

I posted a querry looking for test programs that are designed to
wring out a pic and put it through its paces to see if it is a good
part as far as possible, but I still havent found anything done just
as a thorough chip test program. I've only played with the '877 parts
a llittle, so I am interested in this thread and its eventual outcome.

<3940C14E.8435.AABBEC@localhost> 7BIT

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