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'[PIC]Crystal Oscilator Codes anyone?'
I have a couple of hc18u quartz crystal oscillator.. and I could not find
datasheet on the net.. basically my problem is I dont know if they are
parallel cut or series cut crystal's... and what's recommended capacitor C1
C2 values to use and just incase they are strip cut crystal what resistor to
use.. and I'm not sure of using the recommended values specified in the
microchip datasheets.. should I use them?
The labels on the component says:
hope anybody here knows this component lend a helping hand by ponting me to
the right direction...
thanks a lot...
|On 9/13/06, genome <gmail.com> wrote: jtroxas
> I have a couple of hc18u quartz crystal oscillator.. and I could not find
> datasheet on the net.. basically my problem is I dont know if they are
> parallel cut or series cut crystal's... and what's recommended capacitor
> C2 values to use and just incase they are strip cut crystal what
Unfortunately, you need the data sheet.
They may be parallel or series, may have low or high drive levels, and could
require low to moderate capacitance, assuming they are parallel.
They will almost certainly sing SOME sort of tune in a given circuit, but
they might fracture from overdrive, or give just barely enough level to sort
of run the circuit, most of the time.
Giving cap values in uP app notes is just wrong, unless a particular crystal
is specified. Generally speaking, for your standard parallel rock, double
the Cl value, and subtract a few pF for strays and the chip itself.. If Cl
in the xtal data sheet is 22pF, then 22*2 = 44, - 5pF gives 39pF on each
side. The reason for this is from the crystal's point of view, the caps
are in series.
Paul James E.
For starters, try using caps in the range of 12pf to 33pf or so.
As far as shunt resistor is concerned, it isn't too critical.
However, you want to use a fairly large value (ie..100K to a few megohms).
When you get the oscillator started, measure the frequency. If it is
nearly sopt on, it is probably parallel cut. If it's off a good amount,
it's probably series cut, and the configuration will have to be changed
to get it to oscillate at it's specified (marked) frequency.
Hope this helps.
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