Now we are going to see PIC16F877A LED Interfacing Tutorial (PIC16F877A GPIO Tutorial). If you want to interface LED, you should know Registers used for GPIO. At the end of this tutorial you will be familiar with the PIC GPIO’s and the associated registers for configuring and accessing the GPIO’s.

Prerequisites

• PIC16F877A Introduction

PIC16F877A GPIO Tutorial

Introduction

 PIC16F877A has 33-GPIO’s grouped into five ports namely PORTA to PORTE. They are used for the input/output interfacing with other devices/circuits. Most of these port pins are multiplexed for handling alternate function for peripheral features on the devices. All ports in a PIC chip are bi-directional. When the peripheral action is enabled in a pin, it may not be used as its general input/output functions.

• PORTA
• PORTB
• PORTC
• PORTD
• PORTE

Now we will get into GPIO registers.

GPIO Registers

Register	Description
TRISX	This Register is used for Select that respected IO port as a input or output.
PORTX	This is the IO Port

Note: Here ‘x’ could be A,B,C,D,E so on depending on the number of ports supported by the controller.

TRISX Register

Before accessing the PORTX register, we should declare that port weather input or output. So this register is used to select that direction. If you set 0 that IO port will act as output port. If you set 1 that IO port will act as input port. Just see the snippet below. Then you will understand.

TRISB = 0xff;  // Configure PORTB as Input.
 
TRISC = 0x00; // Configure PORTC as Output.
 
TRISD = 0x0F; // Configure lower nibble of PORTD as Input and higher nibble as Output
 
TRISD = (1<<0) | (1<3) | (1<<6); // Configure PD0,PD3,PD6 as Input and others as Output

PORTX Register

This register is used to read/write the data from/to port pins. Writing 1’s to PORTx will make the corresponding PORTx pins as HIGH. Similarly writing 0’s to PORTx will make the corresponding PORTx pins as LOW. PORTX registers and its alternate functions are shown in below table.

PORT	Number of Pins	Alternative Function
PORTA	6 (PA0-PA5)	ADC
PORTB	8 (PB0-PB7)	Interrupts
PORTC	8 (PC0-PC7)	UART,I2C,PWM
PORTD	8 (PD0-PD7)	Parallel Slave Port
PORTE	3 (PE0-PB2)	ADC

I think this is enough for make code. Let’s move into coding part.

LED Interfacing

Code

In this code I’ve connected LEDs to Port D.

#include<htc.h>

void delay()
{
    unsigned int a;
    for(a=0;a<10000;a++);
}

void main()
{
    TRISD=0;              //Port D is act as Output
    while(1) {
        PORTD=0xFF;   //Port D ON
        delay();
        PORTD=0x00;   //Port D OFF
        delay();
    }
}

Output

[ Please find the output image Here ]

Switch Interfacing

Code

In this code, Switch is connected into Port D. LEDs are connected into Port B.

#include<htc.h>

#define sw RD0                  //Switch is connected at PORTD.0

void delay()
{
    unsigned int a;
    for(a=0;a<10000;a++);
}

void main()
{
    TRISB=0;               //Port B act as Output
    TRISD=0xff;            //Port D act as Input
    while(1) {
        if(!sw) {
            PORTB=0xff;       //LED ON
        } else 
            PORTB=0;          //LED OFF
    }
}

Output

[ Please find the output image Here ]