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Configuring IO Port of PIC18F4550 – The Foundation of Embedded Control

Before diving into advanced modules like ADC, UART, or PWM, every embedded engineer must first understand IO port (General Purpose Input/Output port) — the building blocks of microcontroller programming.

The PIC18F4550 microcontroller comes with powerful, flexible I/O ports that let you read input signals (like switches or sensors) and control output devices (like LEDs, relays, or buzzers).

In this blog, we’ll explore how to configure and use GPIO ports in PIC18F4550 using MPLAB X IDE and the XC8 compiler, through simple and practical examples.

🎯 Goal: After reading this post, you’ll be able to set up I/O pins, blink LEDs, and read switch states — the essential first step to mastering embedded systems.

Understanding IO port in PIC18F4550

PIC18F4550 has five ports: PORTA, PORTB, PORTC, PORTD, and PORTE.
Each port has 8 pins (some with fewer active pins depending on configuration).
Every pin can act as input or output, configured through TRISx registers.

Basic Concepts

Output: Set TRIS bit = 0 → write data to LATx register.

Input: Set TRIS bit = 1 → read data from PORTx register.

Example:

TRISBbits.TRISB0 = 0; // Configure RB0 as output
LATBbits.LATB0 = 1;   // Set RB0 HIGH (LED ON)

TRISBbits.TRISB0 = 0; // Configure RB0 as output
LATBbits.LATB0 = 1;   // Set RB0 HIGH (LED ON)

Example 1: LED Blink Using GPIO

🔧 Hardware Setup

• Connect an LED (with 330Ω resistor) to RB0.
• Connect VSS (GND) to common ground.

#include <xc.h>
#define _XTAL_FREQ 8000000

void main(void) {
    TRISBbits.TRISB0 = 0; // RB0 as output

    while(1) {
        LATBbits.LATB0 = 1; // LED ON
        __delay_ms(500);
        LATBbits.LATB0 = 0; // LED OFF
        __delay_ms(500);
    }
}

#include <xc.h>
#define _XTAL_FREQ 8000000

void main(void) {
    TRISBbits.TRISB0 = 0; // RB0 as output

    while(1) {
        LATBbits.LATB0 = 1; // LED ON
        __delay_ms(500);
        LATBbits.LATB0 = 0; // LED OFF
        __delay_ms(500);
    }
}

✅ Result: The LED connected to RB0 will blink every 500 ms.

Example 2: Switch-Controlled LED

🔧 Hardware Setup

LED → connected to RB0 (output).

Switch → connected to RB1 (input) with pull-down resistor.

#include <xc.h>
#define _XTAL_FREQ 8000000

void main(void) {
    TRISBbits.TRISB1 = 1; // RB1 as input (switch)
    TRISBbits.TRISB0 = 0; // RB0 as output (LED)

    while(1) {
        if(PORTBbits.RB1 == 1)
            LATBbits.LATB0 = 1; // LED ON when switch pressed
        else
            LATBbits.LATB0 = 0; // LED OFF
    }
}

#include <xc.h>
#define _XTAL_FREQ 8000000

void main(void) {
    TRISBbits.TRISB1 = 1; // RB1 as input (switch)
    TRISBbits.TRISB0 = 0; // RB0 as output (LED)

    while(1) {
        if(PORTBbits.RB1 == 1)
            LATBbits.LATB0 = 1; // LED ON when switch pressed
        else
            LATBbits.LATB0 = 0; // LED OFF
    }
}

✅ Result: When you press the switch, the LED lights up!

Important Tips

• Always configure TRIS registers before using any pin.
• Use LATx for writing output and PORTx for reading inputs.
• Use digital input mode (disable ADC on analog pins if needed).

Example:

ADCON1 = 0x0F; // Configure all pins as digital

ADCON1 = 0x0F; // Configure all pins as digital

Common GPIO Applications

• LED indicators and displays
• Push-button or sensor inputs
• Relay and transistor control
• Interfacing digital modules (IR sensor, keypad, etc.)

Next Step: Go Beyond GPIO

Once you master GPIOs, you can easily move on to ADC, Timers, UART, PWM, and Interrupts – all of which depend on correct pin configuration.

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Software development tools & documents:

• MPLAB X IDE
• MPLAB X, XC8 Compiler
• Microchip Technology, pic18f4550

Tag: IO port, GPIO port, Input Output port

💬Frequently Asked Questions (FAQ)