Interfacing PIC18F45Q10 Microcontroller with Seven-Segment Display

• Raja Gupta
• April 26, 2025

This post explains how to drive a common cathode seven-segment display (SSD) with the PIC18F45Q10 microcontroller. We’ll implement a hexadecimal counter (0-F) that cycles through each digit, showcasing how to manipulate output pins to control the display.

What is a Seven-Segment Display (SSD)?

A Seven-Segment Display (SSD) is an electronic display device widely used for showing decimal numbers, hexadecimal values, and even a limited set of alphanumeric characters. It consists of seven LED segments (labeled a to g) arranged in a rectangular pattern and an optional decimal point (DP). By selectively illuminating specific segments, various characters can be displayed.

SSDs are commonly used in digital clocks, calculators, meters, and embedded systems due to their simplicity, low cost, and easy interface with microcontrollers. They are available in common cathode or common anode configurations, depending on whether the common pin is connected to the ground (cathode) or a positive voltage (anode).

Understanding Hex Table

Here’s a table that shows the bit patterns for each digit (0-F) in hexadecimal for a common cathode seven-segment display. Each bit corresponds to a segment (a-g and DP). A 1 lights up the segment, and a 0 turns it off.

How to Read the Table:

1. Hex: The hexadecimal value (0-F).
2. a-g, DP: Represents the state of each segment.
   • 1: Segment is ON.
   • 0: Segment is OFF.
3. Binary Pattern: The full binary pattern for the seven-segment display.
4. Hex Pattern: The binary pattern is represented in hexadecimal.

For example:

• Hex A: Segments a, b, c, e, f, and g are ON, forming the letter A.
• Hex 3: Segments a, b, c, d, and g are ON, forming the digit 3.

Components Needed

1. PIC18F45Q10 Microcontroller
2. Seven-Segment Display (Common Cathode)
3. 220Ω Resistors (x8)
4. Breadboard
5. Jumper Wires
6. External 20 MHz Crystal Oscillator
7. Power Supply (5V)

Circuit Diagram

The seven-segment display will connect to the PORTD of the PIC18F45Q10. Each segment (a to g and DP) is controlled by one bit of PORTD. Resistors are placed in series with each segment to limit the current. The Pin Configuration for the Seven-Segment Display:

1. Connect segments a to g & dp pin to PORTD pins RD0 to RD7 respectively.
2. Connect the common cathode of the display to GND.

Here’s the simple circuit diagram:

Code Breakdown

Here is the code to control the seven-segment display. The microcontroller cycles through hexadecimal digits (0-F) and displays them on the SSD with a delay for visibility.

/*
 * File:   main.c
 * Author: erraj
 *
 * Created on January 5, 2025, 10:08 PM
 */

#include <xc.h>  // Include the header file for the PIC18F45Q10

// PIC18F45Q10 Configuration Bit Settings

// CONFIG1L
#pragma config FEXTOSC = HS    // External Oscillator mode Selection bits (HS mode for crystal above 8 MHz)
#pragma config RSTOSC = EXTOSC // Power-up default value for COSC bits (Use external oscillator)

// CONFIG2L
#pragma config MCLRE = EXTMCLR  // Master Clear Enable bit (MCLR pin (RE3) is MCLR)

// CONFIG3L
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)

#define _XTAL_FREQ 20000000  // Define crystal frequency (20 MHz)

// Segment patterns for common cathode seven-segment display (0-F)
unsigned char segment[] = {
    0x3F, // 0
    0x06, // 1
    0x5B, // 2
    0x4F, // 3
    0x66, // 4
    0x6D, // 5
    0x7D, // 6
    0x07, // 7
    0x7F, // 8
    0x6F, // 9
    0x77, // A
    0x7C, // b
    0x39, // C
    0x5E, // d
    0x79, // E
    0x71  // F
};

void delay_ms(unsigned int ms);

void main(void) {
    // Initialize PORTD as output
    TRISD = 0x00; // Set PORTD as output
    PORTD = 0x00; // Clear PORTB initially

    while (1) {
        // Cycle through 0 to F (hexadecimal)
        for (unsigned char i = 0; i < 16; i++) {
            PORTD = segment[i]; // Display digit on SSD
            delay_ms(300);    // Delay for visibility
        }
    }
}

void delay_ms(unsigned int ms) {
    // Basic delay loop (adjusted for 20 MHz clock)
    while (ms--) {
        __delay_ms(1);
    }
}

Code Explanation:

1. Configuration Bits:
   1. Configured to use an external high-speed crystal oscillator (20 MHz).
   2. Disabled the Watchdog Timer.
2. Seven-Segment Patterns:
   The segment[] array contains the patterns for digits 0-F in hexadecimal. Each byte corresponds to the binary state of the segments (a-g, DP).
3. PORTD as Output:
   1. TRISD = 0x00: Configures all pins of PORTD as output.
   2. PORTD = segment[i]: Displays the corresponding digit by writing the pattern to PORTD.
4. Delays:
   The delay_ms() function introduces a 300 ms delay between each digit for better visibility.

Output

When powered, the seven-segment display will start counting from 0 to F in hexadecimal, with each digit displayed for 300 milliseconds before transitioning to the next.

Watch the Demo Video:

Click here to view the video demonstration!

Conclusion

This project showcases how to interface a seven-segment display with the PIC18F45Q10 microcontroller. By controlling the segments via PORTD, we successfully created a hexadecimal counter. This foundation can be expanded to drive multiple displays or implement more complex applications like displaying sensor data or time.

If you have any questions or want to explore more advanced topics, feel free to leave a comment below. Happy coding!