PIC16F84 Introduction

The 16F84 is deserves looking at because it is the GranDaddy of PIC Microcontrollers but you should not use it for new designs (see Below)...

The PIC16F84 is a the most well known and most well used of all the PIC microcontrollers - it is used in numerous projects that you can find across the web.

Even though the 16F84 is getting on a bit, it is one of the most popular of the PIC microcontrollers and there are hundreds of circuits for it on the web but it does have limited memory, RAM and peripherals (See diagram below). As of 2015 microchip are recommending that you use 16F84A instead of 16F84 with the only difference being that the A-version runs at 20MHz using a 20MHz crystal (the non-A version runs at 10MHz crystal speed only).

It is an 8 bit mid-range microcontroller having 1024 words of program memory, 68 bytes of RAM and 64 bytes of long term EEPROM storage and a single peripheral - an 8 bit timer - Timer0. The real innovation of this device is that it can be re-programmed using ICSP in circuit - and the interesting thing is that this same scheme is used in all PIC devices proving that the design was and is good from the start. The same can be said of Timer0 which is also used throughout the PIC family ranges, although in 18F devices you can set a control bit that turns it into a 16 bit timer. Of course the 8-bit implementation in that device is still the same as the 16F84!

ICSP

The most useful feature of this microcontroller is that it's flash based so  it can be re-programmed many times.  In addition if you design the circuit correctly you can re-program it in-circuit without removing the chip using (ICSP) In Circuit Serial Programming.

Since it is an older device you can not program it using a Low Voltage Programmer (but LVP is only for very specialised usage) - I just turn it off (setting in the control bits that configure a PIC chip) you must use a High Volt Programmer e.g. PICKi3 or PICKit2.


Warning the 16F84 is obsolete.


You can still buy it but it's getting more expensive.


The 16F88,1FF628,16F627 have the same pinout

and are cheaper!

(There are also many other similar chips with different RAM/EPROM/internal peripherals).


Even so if you already have a PIC16F84 then this introduction will show you how to program it with a ICSP programmer. For a comparison between the 16F84 and some other PIC micros (including the 16F88) you can compare bubble diagrams showing PIC features visually here.

In fact the 16F88 is a good PIC micro to progress onto after starting out on the 16F84 as the 16F88 is backwards compatible with the 16F84 -it has the same number of pins and same pin functions.  Some pins are more flexible but still backwards compatible with the 16F84.

Note: You can't easily go from a 16F88 back to a 16F84A, as the 16F88 lets you use pins in a more flexible manner e.g. the 16F88 has an internal oscillator and you can use the crystal oscillator pins either for an external crystal oscillator (as in the 16F84) or as normal I/O pins. This lets the 16F88 have 16 I/O pins as compared to the 16F84 with 13 I/O pins.

For this introduction you need a PIC programmer with an ICSP output connector e.g. PICKit3.

You'll also need to download the C compiler for source code re-compilation (if you want the re-compile code). The compiler is free for the small amounts of code used here.

Jump to Circuit diagram.

PIC 16F84 Index
Features
Programming
ICSP Connection
Power Supply
Oscillator modes
Starter circuit and software


Before you start have a look at the following for background info:  

PIC16F84 Features

The 16F84 is packaged in an 18 pin chip and although it has limited peripherals it is usable in many circuits. Here are its features and a short comparison.

Comparison 16F84 16F88
Program Memory 1024 Words 4096 Words
RAM 68 Bytes 368 Bytes
EEPROM 64 Bytes 256 Bytes
I/O PINS 13 16
PERIPHERALS 1 9
List of peripherals Timer:1 Timers:3, ADC 7 i/ps, 2 Analogue comparators, CCP,SSP, USART


The following bubble diagram shows the major peripherals and features of the 16F84 in a visual format:

16F84

12F675 bubble diagram


Note: You can compare this chip (using bubble diagrams) to some others used on this site by clicking here.

PIC16F84 Programming

You can program the chip using the same ICSP programmer used for the other PIC chips with the circuit shown below and use ICPROG (PC software) to control the programmer hardware from the PC.


You can find a programmer circuit hereand information on using ICPROG here.

PIC16F84 : ICSP connections:

16F84 ICSP connections

PIC16F84 Power Supply

If you don't have a bench power supply then you can use this circuit.

five volt power supplyx


 All you will need is a power supply block with dc output (greater than 8V and no more than 35V) or a 9V battery to plug into CN1.  

Note: It is best to use the 5V power supply circuit as it not only correctly regulates the dc voltage but it protects your PIC chip.  The input voltage can go up to 35V without damaging the 7805 (although the power dissipated by the 7805 will increase for higher input voltages i.e.it wail get hot!) .

7805 pinout

PIC16F84 Oscillator modes

There are four oscillator modes either using an resistor and capacitor pair or a crystal.

PIC16F84 Flashing an LED

16F84 flashing led schematic

Note: The LED current limiter resistor (1k) is not ideal it just lets you see the led (you don't need maximum current to see it) - Replace the 1k with a 220 if you want brighter output.

PIC16F84 Flashing LED

The following code flashes the LED.

Download the source file and hex files here.

You can use the hex file directly to program the 16F84 then it will flash the led on and off or you can re-compile the files using the Mikroelectronika compiler MikroC. 

Some of the PIC16F84 C source code is :

//////////////////////////////////////////////////////////////////////
// Start here for PIC16F84 led flash
//
void main() {
unsigned short pa=0;
unsigned int i;


  PORTA = 0;
  TRISA = 0; // o/p   - sets analogue pins to digital output

  TRISB = 0;
  PORTB = 0;

  while(1) {

     pa=~pa;
     if (pa) {
        setBit(PORTB,3);
     } else {
        resBit(PORTB,3);
     }
     Delay_ms(100);
  } ; // infinite while loop
}


First of all the ports are initialized using TRISA, TRISB which set up the direction of pins for each port - in common with all the other PIC Micros you can change the port direction at any time using  a TRIS keyword (which is just another register location).  

Setting a bit in the TRIS register to zero sets the pin direction to an output.  Here all bits are zero for TRISA and TRISB so all PORTA and PORTB bits are set as outputs.  Then PORTA and PORTB are initialized to logic level zero.

As you can see main() is a very simple it alternately sets and resets bit 3 of PORTB

Try changing the delay time in the delay_ms statements to a smaller or larger value, re-compile and re-program the chip to see the effect.

This gives you the basis for using the PIC16F84 so that you can move on to more complex projects.

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