Hello Jan-Erik,

I use crystal resonators all the time and have never had any problem
with them. This is the first time when PIC marked -20/P refused to work
at 20 MHz. I asked only if someone had the same experience. Tried the
second one (-4/P) to assure myself the fuses are well programmed.

Igor



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Jan-Erik Soderholm
Sent: Friday, March 19, 2004 8:24 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC:] PIC 16F628 an 20 MHz


Igor Pokorny wrote :

> just built Vouter's Wisp628 programmer. It doesn't work because the
> oscilator doesn't start.

I build one a year ago, works just fine. :-)

> I have only two PICs, the second one
> is marked for 4 Mhz.

Exactly how are they marked ?
Mine is marked PIC16F628-20I/P.

> Both work fine at 10 MHz, but none at 20 MHz.

Why do you expect the 4Mhz part to work at all at 20 Mhz ????

> Tried to change capacitors

What capacitiors ?

> and resonators

What type of  "resonators" ?

(You are sure you don't have a crystal? I think you should
anyway...)

> but no result. Both resonators work
> fine with a PIC 16F877. Does someone knows if the maximal frequency
> printed on a chip determines an ability of the oscilator circuit too?

It *is* just that !!!

You leave out far to much to be able to answer better,
I'm afraid...

Regards,
Jan-Erik.

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