Understanding Timers and PWM on ATmega328P

Introduction

Timers are an essential feature of microcontrollers, enabling precise timing operations without blocking the CPU. The ATmega328P includes Timer0, Timer1, and Timer2, each with distinct capabilities. Additionally, Pulse Width Modulation (PWM) allows us to generate analog-like outputs for motor control, LED dimming, and signal generation.

Overview of ATmega328P Timers

The ATmega328P has three hardware timers:

• Timer0: 8-bit, commonly used for delays, timing, and PWM.
• Timer1: 16-bit, ideal for precise timing, servo control, and waveform generation.
• Timer2: 8-bit, similar to Timer0 but also supports asynchronous operation.

Timers work by counting clock cycles and triggering actions when they reach a predefined value. The behavior is configured using prescalers, modes, and interrupts.

Timer Operating Modes

Timers can be operated in different modes:

1. Normal Mode – Simple counting, useful for time measurement.
2. CTC Mode (Clear Timer on Compare Match) – Automatically resets the timer upon reaching a compare value, useful for accurate time delays.
3. Fast PWM Mode – Used to generate PWM signals by varying the duty cycle.
4. Phase Correct PWM Mode – Ensures symmetric PWM signals, commonly used in motor control.

Timer Registers

Timers are controlled using several registers:

Generating Precise Delays Using Timers

Instead of using _delay_ms(), which blocks execution, we can use timers for efficient delays.

Example: Configuring Timer1 for a 1s delay using CTC Mode

#define F_CPU 16000000UL
#include <avr/io.h>
#include <avr/interrupt.h>

void timer1_init() {
    TCCR1B |= (1 << WGM12); // Configure Timer1 in CTC mode
    OCR1A = 15624; // Set compare value for 1s delay (16MHz/1024 prescaler)
    TCCR1B |= (1 << CS12) | (1 << CS10); // Set 1024 prescaler
    TIMSK1 |= (1 << OCIE1A); // Enable Timer1 compare interrupt
    sei(); // Enable global interrupts
}

ISR(TIMER1_COMPA_vect) {
    PORTB ^= (1 << PB5); // Toggle LED
}

int main() {
    DDRB |= (1 << PB5); // Set PB5 as output (LED)
    timer1_init(); // Initialize Timer1
    while (1) {}
}

Explanation:

• Configures Timer1 in CTC mode.
• Uses OCR1A for a 1s delay.
• Uses interrupts to toggle an LED without blocking CPU execution.

Understanding PWM (Pulse Width Modulation)

PWM simulates an analog signal using a digital output by rapidly switching between HIGH and LOW states at a set frequency. The duty cycle determines the proportion of HIGH time in one cycle.

PWM Applications:

• LED Dimming – Controlling brightness smoothly.
• Motor Control – Adjusting speed and direction.
• Signal Generation – Creating analog-like waveforms.

PWM Output Pins:

PWM is available on these ATmega328P pins:

• Timer0: OC0A (PB0), OC0B (PD5)
• Timer1: OC1A (PB1), OC1B (PB2)
• Timer2: OC2A (PB3), OC2B (PD3)

Example: Generating PWM on PB1 using Timer1

#define F_CPU 16000000UL
#include <avr/io.h>

void pwm_init() {
    DDRB |= (1 << PB1); // Set PB1 as output
    TCCR1A |= (1 << COM1A1) | (1 << WGM11); // Fast PWM, non-inverting
    TCCR1B |= (1 << WGM13) | (1 << WGM12) | (1 << CS11); // Prescaler 8
    ICR1 = 19999; // Set TOP value for 50Hz PWM (for servos)
}

void set_duty_cycle(uint16_t duty) {
    OCR1A = duty; // Set duty cycle (0 - 19999)
}

int main() {
    pwm_init();
    while (1) {
        set_duty_cycle(1500); // Example duty cycle for servo motor
    }
}

Explanation:

• Uses Fast PWM mode on Timer1.
• Sets PWM frequency to 50Hz, suitable for servo motors.
• Adjusts duty cycle using OCR1A.

Timers and PWM are fundamental to embedded system programming, enabling precise delays and control over external devices. Mastering these concepts will allow you to build real-time applications efficiently.

In the next post, we will explore UART Communication on ATmega328P, enabling serial communication between microcontrollers and computers. Stay tuned!