Crystal Selection

Amaral

I have a doubt on how to select a crystal for the propeller

On page 29 of the manual it has a table (1-9)

But XOUT Resistance ?? is it the maximum value or it should met with the crystal resistance ?
and the XIN/XOUT Capacitance ? should it match or always above or below ?

I need to buy these parts and can find a safe way to specify it.

thanks in advance

Amaral

Toby Seckshund

The Prop provides its own capacitance and I have not found any Xtal, from my bits box, that haven't worked OK and there are lots of them, provided that they were within the usual range specified.

With pll x 16 4MHz -> 7MHz have worked (but above 5MHz is not "official") and with pll x 8 I have often used 10, 12, and even 14.3MHz.

Are you just wanting to get a system running or are you asking because you need some form of high accuracy ?

Leon

You need to use one with the specified load capacitance if you want the frequency to be reasonably accurate.

Phil Pilgrim (PhiPi)

The Propeller excites a crystal at its parallel-resonant frequency. Crystals spec'd for parallel resonance also provide a required load capacitance to ensure operation at the required frequency. For a 5 MHz crystal, the crystal Parallax sells specs a 20pF load capacitance.

Having said all that, all crystals will operate in serial or parallel resonance. There's no such thing as a solely "series-resonant" or "parallel-resonant" crystal. What the spec refers to is what mode and load capacitance to use to get the frequency stamped on the crystal's can. If you operate outside those specs, the crystal will still oscillate, but at a different frequency.

-Phil