AVR-Chat

1) your code
TCCR1A = (0 << WGM10) | (0 << WGM11);
TCCR1B |= (0 << WGM12); // CTC mode
These 2 lines create a basic CTC mode with maximum count of 0xffff; 
which means that the vlaue in OCR1A is ignored. This would not be the 
correct CTC mode. set WGM12 to 1.

TCCR1B |= (1 << WGM12); // proper CTC mode max is = to value in OCR1A

2) your code
TCCR1B |= (1 << CS12); // Use system clock     CS12 = 1
TCCR1B |= (1 << CS10) | (1 << CS11) | (0 << CS12); // no div, full clock
result is that CS12 = 1 OR 0 = 1,  CS11 =0, and   CS10 = 1
so then from these two lines CS12..10 = 101  which gives a divide clk by 
1024.

dividing clk by 1024 and then counting that to 0xFFFF (65535) and 
toggling divides by 2  that should be a few seconds indeed.

change: TCCR1B |= (0 << WGM12);      to TCCR1B |= (1 << WGM12);
remove : TCCR1B |= (1 << CS12); // Use system clock       now CS12..10 
will be 001   or divide by 1

then tweak the compare match value

rep

On 9/27/2011 10:41 PM, Philippe Habib wrote:
>
> As it turned out, I need timer 0 to run PWM on a pin so I have to use 
> timer 1 for my timer tick.
>
> Using what I learned from timer 0, I was hoping it would be easy to 
> generate a 10ms tick using timer 1.
>
> Here is my setup:
>
> TCCR1A = (0 << WGM10) | (0 << WGM11); // Make sure these are low for CTC
> TCCR1B |= (0 << WGM12); // CTC mode
> TCCR1B |= (1 << CS12); // Use system clock
> TCCR1B |= (1 << CS10) | (0 << CS11) | (0 << CS12); // no div, full clock
> TIMSK1 = (1 << OCIE1A); // Set int for match on A
>
> OCR1A = 64000; // compare value
> // OCR1AH = 0xFF; // MSB
> // OCR1AL = 0x00; // LSB
>
> Here is my ISR
>
> ISR(TIMER1_COMPA_vect)
> {
> PORTD ^= (1 << 6); //Toggle LED
> return;
> }
>
> Using the system clock, I am getting times in the seconds. Am I doing 
> something totally wrong with my timebase, or something else?
>
> Thank you for any light you can shed on this.
>
>