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Thread: Crystal/Capacitor Selection for the hobbiest
www.piclist.com/techref/index.htm?key=crystalcapacitor
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face BY : Mike Knoll email (remove spam text)



I am attempting to select a crystal for a 16F84, running at 4Mhz.  I am
just getting started with PICs.  The PIC datasheet for the 16C84 has a
table instructing me to use two 15pF, one on each pin of the cyrstal,
connected to ground.  But, from ECS's website(http://www.ecsxtal.com), thier 4Mhz
crystal(ECS-40-20-1)) has a load capacitance of 20pF, using the formula on
thier application notes:

      C1 * C2
CL =  ---------  + 5pF
      C1 + C2

Instructs me to use 30pF caps.  (Setting CL=20pF, C1=C2)

Who do I believe?  I've found information out there too general, or too
technical.  The data sheet for the 16F84 seems too general, and I can't
understand too far into MicroChip's app note on crystals.  An index
of commonly avaliable crystals and caps to use would work great.

Also, if series crystals don't need capacitors, why not use them to reduce
parts count?

Also, all instructions I've seen to prevent from over driving the crystal
include using an oscilliscope to measure current.  An oscilliscope is far
from in my budget.  Is there any way to prevent overdriving my crystal
without using an oscilliscope?

Mike

<Pine.SOL.3.96.1000502235658.12109A-100000@lafcol.lafayette.edu>

See also: www.piclist.com/techref/index.htm?key=crystalcapacitor
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