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From: email@example.com (Eitan Herman)
Subject: Re: 8051 clock
Date: 1 Oct 2002 12:53:04 -0700
NNTP-Posting-Date: 1 Oct 2002 19:53:04 GMT
Hello, i did 2 things,
1st - change the capcitors to 15 pF.
2nd - measure these values with X10 scope probe and found: on pin
19:100mv (after x10), pin 18: 5v.
still after changing the capacitors, no clock can be found (what
should be its voltage pick-to-pick values?)
"Tom Faloon" wrote in message news:...
> Hi Eitan,
> 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!
> Tom Faloon
> Eitan Herman wrote in message
> > i connected crystal (3.57Mhz) with 2 small capacitors(800pF) wire like
> > Cap-GND-Cap
> > | |
> > | |
> > 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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