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Fast PWM for ATMega328
#include <avr/io.h>
#include <util/delay.h>
int main(void)
{
pinMode(3, OUTPUT); // output pin for OCR2B, this is Arduino pin number
// In the next line of code, we:
// 1. Set the compare output mode to clear OC2A and OC2B on compare match.
// To achieve this, we set bits COM2A1 and COM2B1 to high.
// 2. Set the waveform generation mode to fast PWM (mode 3 in datasheet).
// To achieve this, we set bits WGM21 and WGM20 to high.
TCCR2A = _BV(COM2A1) | _BV(COM2B1) | _BV(WGM21) | _BV(WGM20);
// In the next line of code, we:
// 1. Set the waveform generation mode to fast PWM mode 7 —reset counter on
// OCR2A value instead of the default 255. To achieve this, we set bit
// WGM22 to high.
// 2. Set the prescaler divisor to 1, so that our counter will be fed with
// the clock's full frequency (16MHz). To achieve this, we set CS20 to
// high (and keep CS21 and CS22 to low by not setting them).
TCCR2B = _BV(WGM22) | _BV(CS20);
// OCR2A holds the top value of our counter, so it acts as a divisor to the
// clock. When our counter reaches this, it resets. Counting starts from 0.
// Thus 63 equals to 64 divs.
// For example, to get 1.6MHz we give it 9. Which will be 16000000 / 10 because counter start at 0.
OCR2A = 63;
// This is the duty cycle. Think of it as the last value of the counter our
// output will remain high for. Can't be greater than OCR2A of course. A
// value of 0 means a duty cycle of 1/64 in this case.
OCR2B = 0;
// Just some code to change the duty cycle every 5 microseconds.
while (1)
{
_delay_us(5);
if ( OCR2B < 63 )
OCR2B += 5;
else
OCR2B = 0;
}
}
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