connecting by pass capacitors to an oscillator in PIC16F84 microcontroller project

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winnie mong

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hi guys for your help on the multiplexed seven segment display

i have another question, i am a project on programmable timer switch using PIC16F84. i am in the design stage and i want to connect by pass capacitors so that the crystal oscillator will operate well.so i need some help on hw to join it to the oscillator and the microcontroller.

thanx in advance
 

If this is a normal crystal then this will specify a capacitive load for typical operation.
The problem will be that circuit layout is unknown and produces a significant capacitance.
The two capacitors for HF work are often around 10pF, hence the layout issue.
Keep the crystal leads close to the component pins, track the capacitors close to these junctions and the other ends straight to the ground plane which should also be close to the micro ground pins, i.e. very short routes and no long tracks.

Note for lower frequencies slightly larger capacitors 20 to 30pF can be used.
Some people suggest no capacitors for the HF crystals, but I avoid this situation as successful oscillation is determined by stray capacitance!
 

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