Using ADC of ATMega328 by Interrupts

[habibparacha]

Hi all,

I am trying to use the ADC of ATMega 328 using its ADC interrupt service routine but it is not working. When I use it without the ISR by just calling the ADC_read() function than it works fine but I have to use it by using the ADC interrupt. The problem is it doesn't even enter the ISR even the global interrupt is also set. I am using PORTB as an indicator whether it goes into particular code area or not.
Infact I am not able to get into any ISR not event the Timer0 Overflow.

Please help Its urgent.

#include <avr/io.h>
#include <inttypes.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <avr/sleep.h>

volatile uint8_t lower;
volatile uint8_t higher;

unsigned int ADC_read(unsigned char ch)
{ 
	ch= ch & 0b00000111;
	ADMUX=(1<<REFS0)|ch;  // reading specified number of pin
 	ADCSRA|=(1<<ADSC);
	while(!(ADCSRA & (1<<ADIF))); 
	ADCSRA|=(1<<ADIF);
	//lower=ADCL;		// ADC registor lower bits
	//higher=ADCH;		// ADC registor upper bits
	//PORTB= ~PORTB;

}

void ADC_init(void)
{
	ADMUX=(1<<REFS0); 
	ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0)|(1<<ADIE);
	sei();
}


ISR(ADC_vect)
{   
	PORTB=~PORTB;
	lower = ADCL;
	higher = ADCH;	
	
}	

int main(void)
{		
    DDRC=0x00; //initialize as input
	DDRB=0xff;
	DDRD=0xc2;
	PORTB=0xff;
	PORTD=0xff;

	ADC_init();
	
	while(1)
	{
		ADC_read(0);
	}		
}

 

[alexan_e]

in the following function remove the red lines and it will work fine

unsigned int ADC_read(unsigned char ch)
{ 
	ch= ch & 0b00000111;
	ADMUX=(1<<REFS0)|ch;  // reading specified number of pin
 	ADCSRA|=(1<<ADSC);
	[COLOR="#FF0000"]while(!(ADCSRA & (1<<ADIF))); [/COLOR]
	[COLOR="#FF0000"]ADCSRA|=(1<<ADIF);[/COLOR]
	//lower=ADCL;		// ADC registor lower bits
	//higher=ADCH;		// ADC registor upper bits
	//PORTB= ~PORTB;

}

The interrupt will execute when the ADIF flag is set and it will be cleared by hardware, there is no point in using a loop to check it and clear it manually.

It is also a good idea to add a small delay of a few us after the channel change and before you start the conversion.

Alex