PIC on breadboard

Discussion in 'Embedded Systems and Microcontrollers' started by bobparihar, Oct 11, 2014.

  1. bobparihar

    Thread Starter Member

    Jul 31, 2014
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    i just want to know the circuit diagram for a 40 pin DIP pic16F877a micro controller..like
    how the external crystal oscillator is attached with the controller and the reset button circuitry and the port connections etc.
    so that i can do its interfacing even on the breadboard with different periphrels
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    This circuit is for a simple security controller, it shows the crystal and reset connections as you requested.
    E
     
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  3. bobparihar

    Thread Starter Member

    Jul 31, 2014
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    thanks for help!
    in some circuits i have seen 22pf capacitors with a 20 MHz crystal for PIC16f877a oscillation circuit.
    why there is variation??
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    I have seen and used both 12pF, 15pF and 22pF and never had a crystal start up problem.

    On a bread board there is sufficient on board capacitance due to the proximity of the rows of the contacts, so the crystal will oscillate without 22pF's.
    I would recommend having cap values between 12pF and 22pF on your final PCB.
    On some layouts you may also see a 1 megohm resistor across the crystal, I have never used a resistor.

    E
     
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  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    33pF worked always Ok for the 16 and 18F families.
     
  6. adam555

    Active Member

    Aug 17, 2013
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    Almost every PIC's datasheet I read comes with a little table like this in the "Oscillator Configuration" section. This one is for the PIC16F88:

    crystal.jpg

    Further down in the same section you can find the different configurations for each type of crystal.
     
    Last edited: Oct 11, 2014
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  7. bobparihar

    Thread Starter Member

    Jul 31, 2014
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    how important are exact values on the capacitors, and is the crystal
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The exact values of the caps is not very critical.
     
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