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Arduino CTC mode output not as expected

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fm101

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I have the following CTC mode arduino code to generate 100khz square wave at pin 6.
C++: 
void setup () {
  //Pin 6 (OC0A) is output
  pinMode(6, OUTPUT);   
   // Load 79 to generate 100 kHz sq.wave
  OCR0A = 79;
   // Toggle OC0A on compare match, WGM 2 (CTC mode)
  TCCR0A = (1 << COM0A0) | (1 << WGM01);
  // Start the timer, no prescalar
  TCCR0B = (1 << CS00);
}

void loop() {

}

But the oscilloscope shows peaked square wave at frequency 7.99MHz and the amplitude is just 765.44mV as shown below.
20220215_015832.jpg

Using delay and microseconds function I was able to generate expected square wave with frequency. But with the above CTC mode code I am not able to generate expected square wave. What could be the problem?
 

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Hi,

What hardware do you use? (Microcontroller, module ...)
What's the system clock frequency?

Klaus
 

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Try setting TCCR0A and TCCR0B to zero so you have everything at 0 to begin with.
Code: 
void setup () {
  //Pin 6 (OC0A) is output
  pinMode(6, OUTPUT);
 
TCCR0B = 0;   // write 0 to timer 0 control registers
 TCCR0A = 0;
 
   // Load 79 to generate 100 kHz sq.wave
  OCR0A = 79;
   // Toggle OC0A on compare match, WGM 2 (CTC mode)
  TCCR0A = (1 << COM0A0) | (1 << WGM01);
  // Start the timer, no prescalar
  TCCR0B = (1 << CS00);
}

void loop() {

}
 
Last edited:

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KlausST said:
Hi,

What hardware do you use? (Microcontroller, module ...)
What's the system clock frequency?

Klaus
Click to expand...
Sorry for late reply, I was out. I am using Arduino Uno which is board based on ATmega328p. Clock frequency is 16MHz. Output frequency desired is 100KHz. Using Timer 0 in CTC mode.
FenTrac said:
Try setting TCCR0A and TCCR0B to zero so you have everything at 0 to begin with.
Code: 
void setup () {
  //Pin 6 (OC0A) is output
  pinMode(6, OUTPUT);
 
TCCR0B = 0;   // write 0 to timer 0 control registers
 TCCR0A = 0;
 
   // Load 79 to generate 100 kHz sq.wave
  OCR0A = 79;
   // Toggle OC0A on compare match, WGM 2 (CTC mode)
  TCCR0A = (1 << COM0A0) | (1 << WGM01);
  // Start the timer, no prescalar
  TCCR0B = (1 << CS00);
}

void loop() {

}
Click to expand...
Yes with the initialization I get closer waveform which is at 34.3KHz but still not getting the calculated 100KHz and the amplitude is just around 590mV.

20220216_071115.jpg



Any further advice? could this be due to the DSO because this is new one?
 
Last edited:

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Before my previous post, I ran your code on my Arduino and received the same 8 Mhz as you experienced. Starting with TCCR0A and TCCR0B zeroed, your code ran with the correct 100khz on pin 6. I suspect that the bootloader may cause the registers to be non zero to start with.
The low voltage you are experiencing and incorrect frequency, Is a separate issue. My arduino, is showing a 10 microsecond waveform with an amplitude of 4.8 volts at pin 6 on the scope.
Check for loading of the signal, probe settings (10x or 1x), and double check scope settings.
Maybe measure frequency with a mutimeter if you have one that will measure the expected signal.
 

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    fm101

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FenTrac said:
Before my previous post, I ran your code on my Arduino and received the same 8 Mhz as you experienced. Starting with TCCR0A and TCCR0B zeroed, your code ran with the correct 100khz on pin 6. I suspect that the bootloader may cause the registers to be non zero to start with.
The low voltage you are experiencing and incorrect frequency, Is a separate issue. My arduino, is showing a 10 microsecond waveform with an amplitude of 4.8 volts at pin 6 on the scope.
Check for loading of the signal, probe settings (10x or 1x), and double check scope settings.
Maybe measure frequency with a mutimeter if you have one that will measure the expected signal.
Click to expand...
Thank you for testing and confirmation.
I now got the correct frequency and amplitude. The attenuation probe setting led to amplitude misread and changes in the OCR value led to the frequency mistake.
 

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