Timer interrupts are a fundamental feature in embedded systems, allowing microcontrollers to perform tasks at precise time intervals without continuous CPU intervention. In the context of microchip microcontrollers, such as those from the PIC and dsPIC series, timer interrupts can be used for a variety of applications including periodic task execution, event counting, and generating precise time delays.

Understanding how to implement timer interrupts is crucial for developing efficient and responsive embedded systems. This article will guide you through the process of setting up and using timer interrupts in a microchip environment, providing practical examples and sample code to illustrate the concepts.

Examples:

Example 1: Setting Up a Timer Interrupt on a PIC Microcontroller

Step 1: Configure the Timer

First, we need to configure one of the available timers. For this example, we will use Timer0 on a PIC16F877A microcontroller.

#include <xc.h>

// Configuration bits
#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF        // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3/PGM pin has PGM function; low-voltage programming disabled)
#pragma config CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

void setupTimer0() {
    // Set up Timer0
    OPTION_REGbits.T0CS = 0; // Select internal instruction cycle clock (FOSC/4)
    OPTION_REGbits.PSA = 0;  // Assign prescaler to Timer0
    OPTION_REGbits.PS = 0b111; // Set prescaler to 256
    TMR0 = 0; // Clear Timer0 register
    INTCONbits.TMR0IE = 1; // Enable Timer0 interrupt
    INTCONbits.TMR0IF = 0; // Clear Timer0 interrupt flag
    INTCONbits.GIE = 1; // Enable global interrupts
    INTCONbits.PEIE = 1; // Enable peripheral interrupts
}

void __interrupt() ISR() {
    if (INTCONbits.TMR0IF) {
        // Timer0 interrupt service routine
        // Add your code here to handle the interrupt
        TMR0 = 0; // Reset Timer0 register
        INTCONbits.TMR0IF = 0; // Clear Timer0 interrupt flag
    }
}

void main() {
    setupTimer0();
    while (1) {
        // Main loop
        // Add your code here
    }
}

Step 2: Compile and Upload the Code

Use MPLAB X IDE and XC8 compiler to compile the code and upload it to your PIC16F877A microcontroller.

Example 2: Using Timer Interrupts on a dsPIC Microcontroller

Step 1: Configure the Timer

For this example, we will use Timer1 on a dsPIC33EP256MU806 microcontroller.

#include <xc.h>

// Configuration bits
#pragma config FNOSC = FRC       // Oscillator Selection bits (Internal Fast RC (FRC))
#pragma config IESO = OFF        // Internal/External Switch Over bit (Disabled)
#pragma config POSCMD = NONE     // Primary Oscillator Mode Select bits (Primary Oscillator disabled)
#pragma config OSCIOFNC = OFF    // OSC2 Pin Function bit (OSC2 is clock output)
#pragma config FCKSM = CSDCMD    // Clock Switching Mode bits (Clock switching and Fail-Safe Clock Monitor are disabled)

void setupTimer1() {
    // Set up Timer1
    T1CONbits.TCKPS = 0b11; // Set prescaler to 256
    TMR1 = 0; // Clear Timer1 register
    PR1 = 15625; // Load period register (for 1 second delay with Fosc = 8 MHz)
    IPC0bits.T1IP = 1; // Set Timer1 interrupt priority
    IFS0bits.T1IF = 0; // Clear Timer1 interrupt flag
    IEC0bits.T1IE = 1; // Enable Timer1 interrupt
    T1CONbits.TON = 1; // Start Timer1
}

void __attribute__((__interrupt__, auto_psv)) _T1Interrupt() {
    // Timer1 interrupt service routine
    // Add your code here to handle the interrupt
    IFS0bits.T1IF = 0; // Clear Timer1 interrupt flag
}

void main() {
    setupTimer1();
    while (1) {
        // Main loop
        // Add your code here
    }
}

Step 2: Compile and Upload the Code

Use MPLAB X IDE and XC16 compiler to compile the code and upload it to your dsPIC33EP256MU806 microcontroller.