Arduino/targets/arduino/wiring_analog.c

/*
  wiring_analog.c - analog input and output
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2005-2006 David A. Mellis

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  $Id: wiring.c 248 2007-02-03 15:36:30Z mellis $
*/

#include "wiring_private.h"

int analogRead(int pin)
{
	unsigned int low, high, ch = analogInPinToBit(pin);

	// the low 4 bits of ADMUX select the ADC channel
	ADMUX = (ADMUX & (unsigned int) 0xf0) | (ch & (unsigned int) 0x0f);

	// without a delay, we seem to read from the wrong channel
	//delay(1);

	// start the conversion
	sbi(ADCSRA, ADSC);

	// ADSC is cleared when the conversion finishes
	while (bit_is_set(ADCSRA, ADSC));

	// we have to read ADCL first; doing so locks both ADCL
	// and ADCH until ADCH is read.  reading ADCL second would
	// cause the results of each conversion to be discarded,
	// as ADCL and ADCH would be locked when it completed.
	low = ADCL;
	high = ADCH;

	// combine the two bytes
	return (high << 8) | low;
}

// Right now, PWM output only works on the pins with
// hardware support.  These are defined in the appropriate
// pins_*.c file.  For the rest of the pins, we default
// to digital output.
void analogWrite(int pin, int val)
{
	// We need to make sure the PWM output is enabled for those pins
	// that support it, as we turn it off when digitally reading or
	// writing with them.  Also, make sure the pin is in output mode
	// for consistenty with Wiring, which doesn't require a pinMode
	// call for the analog output pins.
	pinMode(pin, OUTPUT);
	
	if (analogOutPinToTimer(pin) == TIMER1A) {
		// connect pwm to pin on timer 1, channel A
		sbi(TCCR1A, COM1A1);
		// set pwm duty
		OCR1A = val;
	} else if (analogOutPinToTimer(pin) == TIMER1B) {
		// connect pwm to pin on timer 1, channel B
		sbi(TCCR1A, COM1B1);
		// set pwm duty
		OCR1B = val;
#if defined(__AVR_ATmega168__)
	} else if (analogOutPinToTimer(pin) == TIMER0A) {
		// connect pwm to pin on timer 0, channel A
		sbi(TCCR0A, COM0A1);
		// set pwm duty
		OCR0A = val;	
	} else if (analogOutPinToTimer(pin) == TIMER0B) {
		// connect pwm to pin on timer 0, channel B
		sbi(TCCR0A, COM0B1);
		// set pwm duty
		OCR0B = val;
	} else if (analogOutPinToTimer(pin) == TIMER2A) {
		// connect pwm to pin on timer 2, channel A
		sbi(TCCR2A, COM2A1);
		// set pwm duty
		OCR2A = val;	
	} else if (analogOutPinToTimer(pin) == TIMER2B) {
		// connect pwm to pin on timer 2, channel B
		sbi(TCCR2A, COM2B1);
		// set pwm duty
		OCR2B = val;
#else
	} else if (analogOutPinToTimer(pin) == TIMER2) {
		// connect pwm to pin on timer 2, channel B
		sbi(TCCR2, COM21);
		// set pwm duty
		OCR2 = val;
#endif
	} else if (val < 128)
		digitalWrite(pin, LOW);
	else
		digitalWrite(pin, HIGH);
}