Question

11. Using Timer1 and CTC mode of the ATMega32, write an AVR C program that uses the
hardware waveform generator to generate a square wave on pin OC1A with a
frequency of 50 Hz if PA1 is high, otherwise generate 60Hz. Assume XTAL = 8 MHz.
[10 Marks]

Answer 1

The frequency of the wave is given as

where f_clk_I/O is input clock frequency(clock frequency)

N is the Prescaler

OCRnA is the value in OCRA which is a 16-bit number value from 0 to 65535

So, to produce a wave with 60Hz,

We should have Prescaler to 8 and OCR1A to 8,320

To produce a wave with 50Hz

We should have Prescaler to 8 and OCR1A to 9,999

AVR C Code:

int main(void)
{
   DDRA |= 1<<DDA1;       //Sets PA1 as Output
   TCCR1A |= 1<<COM1A1;   //Clears OC1A on compare match
   TCCR1B |= 1<<WGM12;       //Setting to CTC Mode
   while(1)
   {
       if(PORTA &= 1<<PA1)
       {   //Setting to 50Hz if PA1 is High
           TCCR1B |= 1<<CS11;   //Setting Prescaler to 8
           OCR1A = 9999
       }
       else
       {   //Setting to 60Hz if PA1 is Low
           TCCR1B |= 1<<CS11;   //Setting Prescaler to 8
           OCR1A = 8320;
       }
   }
}