I'm trying to generate an 8MHz clock using PWM, I used the following code:
#include <avr/interrupt.h>
#include <avr/io.h>
/*
Input Frequency -> CLK=16MHz
Timer Resolution = (1 / (Input Frequency / Prescale)) = (Prescale / Input Frequency)
Prescaler Value | Resolution at 16MHz
1 | 62.5nS
8 | 0.6uS
64 | 4uS
256 | 16uS
1024 | 64uS
Target Timer Count = (1 / (Target Frequency * 2)) / (Prescale / Input Frequency) - 1
= (Target Period / 2) / Timer Resolution - 1
If: Target Period = 125nseg. -> Target frequency = 8MHz
With prescaler = 1
Target Timer Count = (125nS/2)/62.5nS - 1 = 0
*/
#define TMR1 0 //for 8MHz: TMR1 = 0 , for 10kHz: TMR1 = 799
void setup() {
pinMode(9, OUTPUT);
//*********************************************************************
//TIMER1 (16 bits) in mode TOP
TCCR1B |= (1 << CS10); //selecting prescaler 0b001 (Tclk/1)
TCCR1B &= ~((1<<CS12) | (1<<CS11)); // turn off CS12 and CS11 bits
TCCR1A |= ((1<<WGM11) | (1<<WGM10)); //Configure timer 1 for TOP mode (with TOP = OCR1A)
TCCR1B |= ((1<<WGM13) | (1<<WGM12));
TCCR1A |= (1 << COM1A0); // Enable timer 1 Compare Output channel A in toggle mode
TCCR1A &= ~(1 << COM1A1);
TCNT1 = 0;
OCR1A = TMR1;
//*********************************************************************
}
void loop() {
}
At lower frequencies I do get the square waves but as I go in the MHz range the wave continues to become distorted and at 8MHz I a get sine wave instead. I was working with OV7670 and in all of its tutorials they generate 8MHz. I think I read that 8MHz PWM for Arduino Uno is really stretching it but I'm wondering if my board in particular can't handle it or it's the oscilloscope ?
