PIC16F84 is one of the very basic and small microncontrollers offered by Microchip. It approves to be the best controllers for beginners and newbies. It offers following fearures;

Operating Speed: Max 20 Mhz.
Input/Output Pins: 13
Current Source/Sink via I/O Pins: 25mA
Interrupts: 4
Timers: 1 Timer of 8-Bit
Watchdog Timer: Yes, with On-Chip RC Oscillator for reliable operation.
In-Ciruit Serial Programming via 2 Pins.

PIC16F84- At a glance

Even though these features are very basic, but they provide a solid base for a beginner to understand the architecture and techniques of using PIC Microcontrollers.

Pinouts:

PIC16F84 Pinouts

The description of the above pins;

Pin 1: RA2Digital I/O.
Pin 2: RA3 Digital I/O.
Pin 3: TOCKI/RA4Clock input for TMR0 Counter/Timer ALSO Digital I/O.
Pin 4: MCLR - Reset Pin (Active Low).
Pin 5: GND - Ground.
Pin 6: INT/RB0 - External Interrupt ALSO Digital I/O.
Pin 7: RB1 -Digital I/O.
Pin 8: RB2 -Digital I/O.
Pin 9: RB3 - Digital I/O.

Pin 10: RB3 - Digital I/O.
Pin 11: RB3 - Digital I/O.
Pin 12: CLK/RB6 - Clock for ICSP(In-Ciruit Serial Programming) ALSO Digital I/O.
Pin 13: DIO/RB7 - Data Input/Output for ICSP ALSO Digital I/O.
Pin 14: +VE - +5v Input.
Pin 15: OSC2/CKO - Osciallator Input PIN#2 ALSO In RC mode, the pin outputs 1/4 of the frequency of OSC1.
Pin 16: OSC1/CKI - Osciallator Input PIN#1 ALSO External clock input.

Baisc Circuit:

Below is the diagram for a basic PIC16F84 circuit, required to run it. Its uses a 4MHz Crystal Osciallator.

Basic Circuit

Other Sources:

The links below provide some good projects running oc PIC16F84;

http://www.ke4nyv.com/picprojects.htm
http://www.piclist.com/techref/piclist/weedfreq.htm

If you have any queries related the usage of PIC16F84, please post in the comments section.

Happy PICing =)