> Thanks for all your replies guys,
>
> I've got it working.

No problem, glad you can move on

> I used a 33 pf cap and a 4.7K resistor.
> I noticed that if the value of the cap is increased,
> the OSC frequency decreases.

And if you increase R also

> I even managed to run without a cap. May be the residual
> capacitance of the PCB was acting.

There will be some stray capacitance but I wouldn't rely
on it being either constant because of humidity, temperature,
closeness of other devices etc or the same as another board.
You will be best to put a known C in and then you don't have
to worry about it

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