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From: John Woodgate
Subject: Re: 8051 clock
Date: Sat, 5 Oct 2002 11:15:53 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sun, 6 Oct 2002 10:46:57 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Eitan Herman
wrote (in <67c4ed7e.0210050140.51f8888b@posti
ng.google.com>) about '8051 clock', on Sat, 5 Oct 2002:
>when i'm using the 8051 with crystal and 2 small caps - outside the
>original circuit that i described below , it's working fine.
>so something in my circuit load it and make it stop working...
>what can it be?
There isn't really anyway to tell, without examining your printed board
in detail. But you measured unexpected voltages on XTAL1 and XTAL2 on
the board. What voltages do you measure on the working circuit?
Quote from Tom Falloon's post:
Your DC values are bad. You should see a DC voltage close to mid rail on
both XTAL1 and XTAL2.(Measure these voltages only with a DVM having 10M
input impedance, or with a X10 (10M) scope probe. A lower impedance
meter could give a misleading reading at XTAL1, depending on the value
of the (internal) feedback resistor.)
You may have a short-circuit from XTAL2 to Vcc on the printed board.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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