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

 

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

 

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

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

 

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

 

33pF worked always Ok for the 16 and 18F families.

 

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

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:



Further down in the same section you can find the different configurations for each type of crystal.

 

how important are exact values on the capacitors, and is the crystal

 

The exact values of the caps is not very critical.