AVR atmega8 problem :(

seta45 said:

Hi misterT,
I am sorry but I still don't understand. As I understood, OCR1A set the top value, and the TCNT1 will be incremented until it is equal OCR1A. I don't know how to use OCR1B in this one. Sorry if I misunderstood something, as I am very new to AVR.

Click to expand...

seta45 said:

Hi there,

I want to generate a square wave with certain frequency but the output frequency is smaller by a factor of 10 than what I expected.
To test it out I make this code. I use the internal 4Mhz clock (I also checked it with my 4 Mhz crystal). I expect to get a 1 Mhz wave out (since I counted to 3), but I only get 100 kHz.

#include <avr/io.h>
#define F_CPU 4000000UL
// initialize timer, interrupt and variable
void timer1_init()
{
TCCR1B |= (1 << WGM12)|(1 << CS10);
// initialize counter
TCNT1 = 0;
// initialize compare value
OCR1A = 3;
}
int main(void)
{
// connect led to pin PC0
DDRC |= (1 << 0);
timer1_init(); // initialize timer

while(1) // loop forever
{
if (TIFR & (1 << OCF1A))
{
PORTC ^= (1 << 0); // toggles the led
}
// clear flag bit by writing '1' to it (as per the datasheet)
TIFR |= (1 << OCF1A);
}
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I also made this code, hoping to get the 4 Mhz out, but only get 400 kHz.

#include <avr/io.h>
#include <util/delay.h>
#define F_CPU 4000000UL
int main(void)
{
// connect led to pin PC0
DDRC |= (1 << 0);
while(1) // loop forever
{
PORTC ^= (1 << 0); // toggles the led
}
}

I use AVR studio 4 btw. I use a oscilloscope to measure the output wave. I also checked the code in Proteus.
I think I got the fuse bits right. When I use the second code with a 8 Mhz internal clock, I got 800 kHz out.
Please help me point out what I did wrong.

Click to expand...

#include <avr/io.h>

int main(void) {
	DDRD	= (1 << 5);
	TCCR1A	= (1 << COM1A0);
//	OCR1A	= 0;
	TCCR1B	= (1 << WGM12) | (1 << CS10);	

	for(;;);
}