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From: "Tom Faloon"
Subject: Re: 8051 clock
Date: Mon, 30 Sep 2002 22:35:39 +0100
NNTP-Posting-Date: Mon, 30 Sep 2002 23:27:51 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
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
If the levels are wrong, remove the crystal & caps, and find out why. (Maybe
a solder fault, or even lots of flux on the board. Clean the board well in
this area, look for faults.) Don't fit crystal or caps ontil both XTAL1 &
XTAL2 have a DC level near mid rail.
Your capacitor values seem very large. Fit values recommended by the crystal
manufacturer. More likely to be in the 10pF to 50pF range!
Eitan Herman wrote in message
> i connected crystal (3.57Mhz) with 2 small capacitors(800pF) wire like
> | |
> | |
> 19 18
> i can see vcc on pin 18 and something like 1.2 volt on pin 19.
> no clock showing(checked with scope).
> 1.what should i do (or what's wrong- need smaller cap?)
> 2.how can i solve it.
> 3.can i use low 555 clock for testing?
> thanks in advance,
> Eitan Herman.
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