// PIC18F4321 Configuration Bit Settings
#pragma config OSC = HS     // HS oscillator (8MHz crystal)
#pragma config WDT = OFF    // Watchdog Timer disabled
#pragma config LVP = OFF    // Low-Voltage Programming disabled
#pragma config PBADEN = OFF // PortB<4:0> pins are configured as digital I/O on Reset
 
#include <xc.h>
 
#define _XTAL_FREQ 8000000 // 8 MHz Crystal
 
volatile unsigned int seconds = 0;
volatile unsigned int minutes = 0;
volatile unsigned int hours = 0;
 
void timer0_init() {
    T0CONbits.T08BIT = 0;   // 16-bit Timer
    T0CONbits.T0CS = 0;     // Internal instruction cycle clock (Fosc/4)
    T0CONbits.PSA = 0;      // Prescaler assigned
    T0CONbits.T0PS = 0b110; // Prescaler 1:128
    TMR0H = 0x0B;           // Preload high byte
    TMR0L = 0xDC;           // Preload low byte (for 1 second interrupt approx.)
    INTCONbits.TMR0IE = 1;  // Enable Timer0 interrupt
    INTCONbits.TMR0IF = 0;  // Clear Timer0 interrupt flag
    T0CONbits.TMR0ON = 1;   // Turn on Timer0
}
 
void interrupt isr() {
    if (INTCONbits.TMR0IF) {
        TMR0H = 0x0B;       // Reload for next interrupt
        TMR0L = 0xDC;
        INTCONbits.TMR0IF = 0; // Clear interrupt flag
 
        // Increment time
        seconds++;
        if (seconds >= 60) {
            seconds = 0;
            minutes++;
            if (minutes >= 60) {
                minutes = 0;
                hours++;
                if (hours >= 24) {
                    hours = 0;
                }
            }
        }
    }
}
 
void main() {
    // Configure interrupts
    INTCONbits.GIE = 1;   // Enable Global Interrupts
    INTCONbits.PEIE = 1;  // Enable Peripheral Interrupts
 
    timer0_init();
 
    while (1) {
        // Main loop does nothing; everything handled in interrupt
        // You could add LCD code here to display the time
        // For example: lcd_display(hours, minutes, seconds);
    }
}
 

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