EG-151 - Lecture 6: Atmel ATmega326 ADC Example

main.c

/*
PORTD maps to Arduino digital pins 0 to 7
DDRD - The Port D Data Direction Register - read/write
PORTD - The Port D Data Register - read/write
PIND - The Port D Input Pins Register - read only

PORTB maps to Arduino digital pins 8 to 13 The two high bits (6 & 7) map to the crystal pins and are not usable
DDRB - The Port B Data Direction Register - read/write
PORTB - The Port B Data Register - read/write
PINB - The Port B Input Pins Register - read only

PORTC maps to Arduino analog pins 0 to 5. Pins 6 & 7 are only accessible on the Arduino Mini
DDRC - The Port C Data Direction Register - read/write
PORTC - The Port C Data Register - read/write
PINC - The Port C Input Pins Register - read only
*/

#include <stdint.h>

//I/O and ADC Register definitions taken from datasheet
#define PORTB  (*(volatile uint8_t *)(0x25))
#define DDRB   (*(volatile uint8_t *)(0x24))
#define PINB   (*(volatile uint8_t *)(0x23))

#define ADMUX  (*(volatile uint8_t *)(0x7C))
#define ADCSRA (*(volatile uint8_t *)(0x7A))
#define ADCRSB (*(volatile uint8_t *)(0x7B))
#define ADCH   (*(volatile uint8_t *)(0x79))
#define ADCL   (*(volatile uint8_t *)(0x78))
#define DIDR0  (*(volatile uint8_t *)(0x7E))

uint16_t adc_result, previous_result = 0;
uint8_t  adc_result_low, adc_result_high;


int main(void)
{
	// Set Data Direction Registers
	DDRB = DDRB | 0b00111111; //Setup bits 0 - 5 of port B as outputs

	// Turn all LEDs off
	PORTB = PORTB & 0b11000000; // Pins B0 (D8) - B5 (D13) start low
	
	// Set up ADC on pin A0
	DIDR0 = DIDR0 | 0b00000001; // Disable pin A0 as a digital input
	
	ADMUX = 0b01000000; // Select reference voltage, right adjusted result and select channel ADC0 - A0

	ADCSRA = ADCSRA | 0b00000111; // Select ADC Prescaler

	ADCSRA = ADCSRA | 0b10000000; // Enable ADC
	
	for(;;)
	{
		ADCSRA = ADCSRA | 0b01000000;		//start conversion by writing 1 to the ADSC bit
		
		while((ADCSRA & 0b01000000) != 0) { }	//wait until the ADSC bit changes to 0
		adc_result_low = ADCL;			//read the low byte of the result into adc_result_low
		adc_result_high = ADCH;			//read the high byte of the result into adc_result_high
    		/* shift whole 8 bits of ADC high byte into most significant byte of ADC result and 
       		   add in ADC low byte using bitwise OR. */
		adc_result = (adc_result_high<<8) | adc_result_low; 
		
		if (previous_result < adc_result)
		{
			if (adc_result >= 854) {PORTB = PORTB | 0b00111111;}
			else if (adc_result >= 684) {PORTB = PORTB | 0b00011111;}
			else if (adc_result >= 513) {PORTB = PORTB | 0b11001111;}
			else if (adc_result >= 342) {PORTB = PORTB | 0b11000111;}
			else if (adc_result >= 171) {PORTB = PORTB | 0b11000011;}
			else if (adc_result >= 1) {PORTB = PORTB | 0b11000001;}
			else PORTB = PORTB & 0b11000000;
		}
		else if (previous_result > adc_result)
		{
			if (adc_result >= 854) {PORTB = PORTB & 0b11111111;}
			else if (adc_result >= 684) {PORTB = PORTB & 0b11011111;}
			else if (adc_result >= 513) {PORTB = PORTB & 0b11001111;}
			else if (adc_result >= 342) {PORTB = PORTB & 0b11000111;}
			else if (adc_result >= 171) {PORTB = PORTB & 0b11000011;}
			else if (adc_result >= 1) {PORTB = PORTB & 0b11000001;}
			else PORTB = PORTB & 0b11000000;
		}
		else{}
		previous_result = adc_result;
	}
	
}