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xtal load capacitance help

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david90

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xtal load capacitance

I bought this xtal from jameco.com and it has no load capacitance cap value. Instead it says "series capacitance." What does it mean? I don't need any caps?

The model number for the xtal @ jameco is CYX006-8. It is an 8Mhz xtal.
 

FoxyRick

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placement of load res for xtal

Looks like you have a crystal calibrated for use in a series-resonant circuit. Most (all?) MCU's have a crystal oscillator circuit designed for parallel-resonant crystals.

The two modes differ only slightly in frequency, and the crystal will be forced into one of the modes by the design of the driving circuit.

So, the MCU will likely try to drive the crystal into parallel-resonance. If you don't add capacitors, it may not oscillate. If you do (and you'll have to take a guess at the values - 20-30pf ???) then it may oscillate, but not at 8MHz.

If the exact timing isn't critical, give it a go with the capacitors, it will probably work OK.

Next time, buy parallel-resonant ;-)

You may find these resources useful:

http://www.radio-electronics.com/info/data/crystals/xtals.php
http://www.euroquartz.co.uk/pdf/tech-notes.pdf

Cheers,
FoxyRick.
 

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