avr_demo/adxl335/analog.c

/*
 * Analog to digital conversion routines for Atmel.
 * 
 * Copyright 2011 Mika Tuupola
 *
 * Licensed under the MIT license:
 *   http://www.opensource.org/licenses/mit-license.php
 *
 */
 
#ifndef ADC_REF
#define ADC_REF          ADC_REF_VCC
#endif

#include <avr/io.h>
#include "analog.h"

uint16_t analog_read(uint8_t pin) {
    
    /* Enable ADC and set prescaler. */
    ADCSRA = _BV(ADEN) | ADC_PRESCALER;
    
    /* Set high speed mode. */
    ADCSRB |=  _BV(ADHSM);
    
    /* Set adc reference and select mux. */
    ADMUX = ADC_REF | (pin & 0b00011111);
    
    /* Start conversion. */
    ADCSRA |= _BV(ADSC);
    
    /* Wait until adc has result ready. */
    loop_until_bit_is_clear(ADCSRA, ADSC);

    /* Word! */
    return ADCW;
}

uint8_t analog_read_byte(uint8_t pin) {
    
    /* Enable ADC and set prescaler. */
    ADCSRA = _BV(ADEN) | ADC_PRESCALER;
    
    /* Set high speed mode. */
    ADCSRB |=  _BV(ADHSM);
    
    /* Set adc reference and select mux. */
    ADMUX = ADC_REF | (pin & 0b00011111);
    
    /* Left adjust the 10 bit result. */
    ADMUX  |=  (1<<ADLAR);
    
    /* Start conversion. */
    ADCSRA |= _BV(ADSC);
    
    /* Wait until adc has result ready. */
    loop_until_bit_is_clear(ADCSRA, ADSC);

    /* Hight byte. */
    return ADCH;
}