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'[SX]:Oscillator question'
2000\11\30@041733 by rubenj

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Hello all,

I have a design with a SX18 which originally used the internal RC-osc
at 4 MHz. At tests it has showed that this is not accurate enough. I
then switched to a 4MHz ceramic resonator to get better accuracy. I
also have a header with connections to the both osc-pins, 5V and 0V,
used for programming and debugging. However, when I touch this header
with my fingers (the osc-pins) the oscillator frequency goes off and
sometimes the oscillator also stops and won't start again unless I
cycle the power off and on again.

Is this normal behavior or is it something I should be worried about?
Would the same happen if I use a crystal instead?

Thanks in advance / Ruben
==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
spam_OUTrubenTakeThisOuTspampp.sbbs.se
==============================

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2000\11\30@115758 by Dan Michaels

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Ruben Jvnsson wrote:
>Hello all,
>
>I have a design with a SX18 which originally used the internal RC-osc
>at 4 MHz. At tests it has showed that this is not accurate enough. I
>then switched to a 4MHz ceramic resonator to get better accuracy. I
>also have a header with connections to the both osc-pins, 5V and 0V,
>used for programming and debugging. However, when I touch this header
>with my fingers (the osc-pins) the oscillator frequency goes off and
>sometimes the oscillator also stops and won't start again unless I
>cycle the power off and on again.
>
>Is this normal behavior or is it something I should be worried about?
>Would the same happen if I use a crystal instead?
>

Hello Ruben, there are many different oscillator selections
on the SX chips, and you might try other selections to see if
something else is more stable. There are also "long" sheets of
errata notes for the SX parts, and you might look thru those
too.

- dan michaels

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2000\11\30@143313 by MIKE

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Yes your fingers will effect/stop the oscillator.
The 'oscillator in' pin in the circuit will be adversly affected by
noise,capacitance and leakage to earth, for this reason I would normally
keep the connections between the xtal/resonator and the device short. I
would not reccomend having it connected to other connectors or anywhere
where it might come into contact or influence of other circuits etc. If it
is being driven by a low impedance source such as an oscillator module then
a more relaxed aproach can be taken.



Regards

Mike Pearce

Neutronics



Hello all,

I have a design with a SX18 which originally used the internal RC-osc
at 4 MHz. At tests it has showed that this is not accurate enough. I
then switched to a 4MHz ceramic resonator to get better accuracy. I
also have a header with connections to the both osc-pins, 5V and 0V,
used for programming and debugging. However, when I touch this header
with my fingers (the osc-pins) the oscillator frequency goes off and
sometimes the oscillator also stops and won't start again unless I
cycle the power off and on again.

Is this normal behavior or is it something I should be worried about?
Would the same happen if I use a crystal instead?

Thanks in advance / Ruben
==============================
Ruben Jvnsson
AB Liros Elektronik
Box 9124, 200 39 Malmv, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
.....rubenKILLspamspam@spam@pp.sbbs.se
==============================

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