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Colpits blocking cap value for MC9S12DP256

Question asked by Kevin Huffman on Oct 20, 2012
Latest reply on Oct 21, 2012 by Kevin Huffman

Freescale recommends use of a blocking cap with the MC9S12DP256 Colpits clock circuit.  The cap blocks DC voltage between Extal and the crystal.  It is referred to as C11 in the Developer User's Guide (V2.05).  What is a recommended value for C11 if the device is using a 16 MHz crystal with 18 pF caps?  Apparently this cap is recommended to limit DC voltage applied to the crystal (thereby reducing crystal life expectancy) and minimizing startup issues.