Basic Circuit Of PIC16F877A

Basic Circuit Of PIC16F877A

Power Supply

To start up your PIC16F877A, there are 7 pins you should connect correctly. Likes others electronic component, the supply pin is the most important. The ideal voltage for PIC16F877A is 5V (Direct Current). It should not be higher then 5.5V because it going to blow up. It also should not be less then 2V because it not going to be operate. You will have various type of supply such as battery and DC adapter. The problem is, if you use battery, it hard to fine normal battery in 5V. Yes you can use 3 normal 1.5V battery that connected in series. But I don’t think it will be efficient enough. So how if I use 9V battery? Yes I can use it but I need to step it down to 5V. How? You can use voltage regulator. LM7805 the part number of the voltage regulator that I used. The two number at the end of the part number is 05 which is mean it will step down the larger input voltage to 5V. Let say if use LM7809 it will step down the higher voltage then 9V to 9V. Here is the datasheet. This is the basic connection to step down 9V to 5V by using LM7805.

Using LM7805 is not only limited to battery supply source. But you can also use it at your rectifier circuit. Picture below show how the connection from the output of rectifier to the LM7805 and to PIC16F877.

Reset Pin

So, how to give power supply to PIC is already covered. As I said before, there are 7 pins should be connect in order to let your PIC operate. 4 pins is already connected which is 2 pins for 5V and 2 pin for ground (negative). It 3 more pins left. The other important pin is Reset pin (MCLR - Master Clear Reset at Pin number 1). If PIC read 0V at MCLR pin, it will reset the program, so if you not connect the MCLR pin with 5V, PIC will remain reset and your program will not execute. You can directly connect the MCLR with 5V (series with resistor likes picture below) but you will unable to reset if your system goes wrong.

If you want to use the reset function, you need to create logic condition which is 1 and 0 to the reset pin. 1 is mean the reset pin get 5V. If the reset pin logic is 1, then the program in your PIC will execute, but if the reset pin logic condition is 0 (which is 0V) then your PIC will not execute the program.

Logic Condition	Voltage	Program Status
0	0V	Not Execute
1	5V	Execute

So, how you can get this condition? The answer is simple, you just need a switch. But you cannot simply add a switch between the 5V and the reset pin. You will need the Pull Up Resistor. What is that thing? See the picture below, that is the correct way how to add up a switch in order to create the logic condition.

When the switch is not pushed, current will flow trough 10K resistor and MCLR Pin. As a result, MCLR Pin receive 5V and PIC read it as logic 1. But when switch is push, current will flow through 10K resistor, switch and directly to ground. There is no voltage will receive at MCLR Pin. This give 0 logic at MCLR Pin.

The Oscillator

Five from seven of important pins already covered, now there are only 2 pin left which is pin number 13 and 14. Those pin was named as OSC1 and OSC2. You can connect the crystal osillator from various frequency. Pulse generated from the oscillator will some time have the noise. To reduce the noise, two capacitors in piko farad value is needed. The value of capacitor is depend on the speed of oscillator that you use. Here is the way how to connect the the crstal oscillator and capacitor value table.

VCC (+5V)	GND
PIN 11	PIN 12
PIN 32	PIN 31