can you please also check if the crystal is a serial cut from the supplier? Funny N. New Bedford, MA http://www.AuElectronics.selfip.com ----- Original Message ---- From: John Chung To: Microcontroller discussion list - Public. Sent: Thursday, December 20, 2007 7:48:55 PM Subject: Re: [PIC]: 16F877 oscillator does not work at 20MHz --- Bob Axtell wrote: > John Chung wrote: > >> Second, it is almost impossible to actually be > >> certain that a 20M > >> crystal is oscillating on frequency. > >> > > > > > > Why is it so? I used a scope frequently across the > > crystal to view the freq it is running at. > > > > John > > > > > > > > > ____________________________________________________________________________________ > > Never miss a thing. Make Yahoo your home page. > > http://www.yahoo.com/r/hs > > > because most oscilloscopes have a low input > impedance and a high enough > capacitance to prevent the oscillator from > oscillating properly. If yours works that's great. > Most of us have > scopes and probes that load down the oscillator when > probed. Lower frequencies, such as 4Mhz, are not > usually affected > because of the lower frequency. > > --Bob > -- Hmm. I haven't thought of it that way. Looks like I need to draw out the datasheet for the crystals before I start probing them. The current crystal I used are pretty *documentless*...... Thanks for the explanation Bob. Now I need to draw out some paper and pencil to calculate how far does my scope go.......... Thanks, John Chung ____________________________________________________________________________________ Never miss a thing. Make Yahoo your home page. http://www.yahoo.com/r/hs -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist ____________________________________________________________________________________ Looking for last minute shopping deals? Find them fast with Yahoo! Search. http://tools.search.yahoo.com/newsearch/category.php?category=shopping -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist