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ATMega328P generating PWM with timer2

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I'm trying to generate a PWM singlal with timer2 module of ATMega328P. Say I want to generate a 50% duty cycle signal. I have attached a DC motor at the output OOC2A(RB3) to see the value of the signal.

I wrote this code: Initialised TMR2 in fast pwm non inverting mode. My freq is 1Mhz and I used /8 prescaler option.
From my understanding OCR2A is the duty cycle when TMR2 is in PWM mode. Now since TMR2 is an 8-bit timer from my understanding writing 255 in OCR2A means 100% duty cycle. And 127 means ~50% duty cycle. So I wrote 127 in the OCR2A and expected a 50% duty cycle. Please correct me if I'm wrong here.
WHen I run the code the motor runs full speed no matter the value which I put in the OCR2A register :(. Am I missing something here?

 * AVRGCC1.c
 * Created: 2/19/2017 4:28:32 PM
 *  Author: Jarvis

#include <avr/io.h>
#include <util/delay.h>
#define F_CPU 1000000L

void pwm_init()
    // initialize TCCR2 as: fast pwm mode, non inverting
    TCCR2A |= (1<<COM2A1) | (1<<COM2A0) | (1<<WGM21) | (1<<WGM20);
    TCCR2B |= (1<<CS21); // clkT2S/8 prescale
    // OC2RA pin made as output 
    DDRB |= (1<<PB3);

int main(void)
     OCR2A = 127;    


Active Member
The code seem's to be right.
Have You disconnected the motor and measured the signal with an oscilloscope?
You can simulate the code with AVR Studio 7.

You have attached a free wheeling diode to the Motor?


I've edited some stuff in the code and it runs fine now for small duty cycles. If I give it a high duty cycle the motor does not start.


Active Member
I think the PWM generation will not be the problem.
In the L293 datasheet i've seen that the t/on time ist about 700ns for the half amplitude of output signal.
I think that ist the time from input signal to output signal.
For the enable pin is explicid not time given in the datasheet.

I would suggest You to test the time from rising the enable pin to the output signal with an 2 channel oscilloscope.
Possibly at one point the pulses from the PWM are to short for the L293, and so the Motor wouldn't start.
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