Problem with Timer 3 Atmega1281

Forum 2005-2010 (read only) Software Syntax & Programs
1

Hello,

I am using Atmega1281 with a 8Mhz frequency. I am trying to configure the Timer3 as CTC mode without prescaler:

TCCR3A= 0xC0;
OCR3A=0x00F0;
TCCR3A= 0x40;
TCCR3B= 0x09;

I do not understand why I get some cycles of 20 microseconds and others with 40 microseconds.

If I change the pulse frequency:
OCR3A=0x00A0;
Then I get cycles of 20 microseconds but every 3.2 milliseconds a get a strange cycle.

Do you know what is the problem?
Thank you very much.

2

How are you measuring the length of your cycles? Is it possible that your measuring equipment is not set up to measure periods this small?

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3

I am using an oscilloscope Handyscope HS3. I can see the cycle every 20 microseconds.

4

Meh...I would blame the scope. I've never trusted those PC-based models to provide quality results. See if you can get your hands on a real bench scope to confirm your observations, as I don't see any reason why you should be observing "hiccups" in your timer output.

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5

You were right, the oscilloscope was the problem.