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S08QE8 32.768KHz external crystal hardware?

Question asked by iansmusical on Jul 17, 2014
Latest reply on Aug 11, 2014 by iansmusical

Hello All,

 

Looking at the QE8 datasheet/reference manual, I see that it's possible to directly connect a 32.768KHz crystal across the XTAL pins, without capacitors providing that the RANGE and HGO bits in ICSC2 are 0. However, the chips built in capacitors are not likely to be the same as the crystal capacitor load and therefore the frequency won't be optimal?

 

To get the optimal frequency I'd have to include external capacitors and set the HGO bit to 1? How do I simply calculate the Rf and Rs resistors? I have read application notes and while it seems easy to calculate the capacitor values, the other two values seem a bit of a mystery!? ;-)

 

Thanks,

 

Ian

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