// PIC18 in C - Versione 0.1 - Luglio 2014
// Copyright (c) 2014, Vincenzo Villa
// Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.
// Creative Commons | Attribution-Share Alike 3.0 Unported
// https://www.vincenzov.net/tutorial/PIC18/timer0.htm

// Reference: PIC18F14K50 data sheet (note: page as DS41350C printed edition)

// [1] REGISTER 2-1: OSCCON: OSCILLATOR CONTROL REGISTER - Page 16
// [2] REGISTER 9-12: TRISC: PORTC TRI-STATE REGISTER - Page 90
// [3] REGISTER 9-11: PORTC: PORTC REGISTER - Page 90
// [4] REGISTER 7-10: RCON: RESET CONTROL REGISTER - Page 74
// [5] REGISTER 7-2: INTCON2: INTERRUPT CONTROL 2 REGISTER - Page 66
// [6] REGISTER 7-1: INTCON: INTERRUPT CONTROL REGISTER - Page 65
// [7] REGISTER 10-1: T0CON: TIMER0 CONTROL REGISTER - Page 97
// [8] TABLE 10-1: REGISTERS ASSOCIATED WITH TIMER0
// [9] REGISTER 9-13: LATC: PORTC DATA LATCH REGISTER

#define _XTAL_FREQ 1000000 // Default PIC18F14K50 clock [1]

#define TIMER0_VALUE 3036 // See text - 0,5 Hz blink

#include "configurationsbits.h"

void interrupt __low_priority my_isr_l(void) {
    if (INTCONbits.TMR0IF == 1) // Interrupt from Timer0? [6]
    {
        TMR0H = TIMER0_VALUE >> 8; // Write 8 MSB to Timer0 [8] - BEFORE!
        TMR0L = TIMER0_VALUE & 0xFF; // Write 8 LSB to Timer0 [8]

        LATCbits.LC1 = ~LATCbits.LC1; // Change LEDs status [9]
        INTCONbits.TMR0IF = 0; // Clear interrupt status [6]
    }
}

void main(void) {

    TRISC = 0x00; // Set PORTC as output [2]
    PORTC = 0; // Turn off all LED [5]

    RCONbits.IPEN = 1; // Enable priority levels on interrupts [4]

    T0CONbits.T08BIT = 0; // Timer0 is configured as a 16-bit timer/counter [7]
    T0CONbits.T0CS = 0; // Internal instruction cycle clock (_XTAL_FREQ / 4 = 250 kHz) [7]
    T0CONbits.PSA = 0; // Timer0 prescaler is assigned. Timer0 clock input comes from prescaler output [7]
    T0CONbits.T0PS = 0b001; // 1:4 prescale value [7]

    TMR0H = TIMER0_VALUE >> 8; // Write 8 MSB to Timer0 [8] - BEFORE!
    TMR0L = TIMER0_VALUE & 0xFF; // Write 8 LSB to Timer0 [8]

    INTCON2bits.TMR0IP = 0; // Set low priority interrupt [5]
    INTCONbits.TMR0IE = 1; // Enables the TMR0 overflow interrupt [6]
    INTCONbits.GIEL = 1; // Enables all low priority interrupts [6]
    INTCONbits.GIEH = 1; // Enables all interrupts [6]

    T0CONbits.TMR0ON = 1; // Enable Timer0 [7]

    while (1) { // 5 Hz LED blink, forever
        LATCbits.LC0 = ~LATCbits.LC0;
        __delay_ms(100);
    }
}