Aref핀 (AVR)

http://www.engineersgarage.com/embedded/avr-microcontroller-projects/adc-circuit

- AVCC : 아날로그 VCC가 연결되는 핀입니다.
- AREF : 아날로그 VCC의 기준 전압이 되는 핀입니다.

▼Datasheet에 나와있는 내용

AVCC : AVCC is the Analog Supply Voltage pin for Port F and the A/D Converter. 

It should be externally connected to VCC, even if the ADC is not used. 

If the ADC is used, it should be connected to VCC through a low-pass filter.

(Ranage : Vcc-0.3 ~ Vcc+0.3)

▼Link

The Atmega168 has 2 digital supply voltage pins, VCC and AVCC. 

AVCC supplies power to PC0-PC5. 

When these pins are used as analogue inputs, the AVCC power needs to be very stable.

This is achieved by using a low pass filter comprising of an inductor and capacitor.

(방금 위에서 언급했던 내용)

 

AREF : AREF is the analog reference pin for the A/D Converter.

(Aref = Vref)

AVCC, AREF를 함께 short시키고 Vcc로 묶어서 연결

//Program for ADC to read from channel 0 and show the 8 bit o/p on PORTB 

 

#include<avr/io.h>

#include<util/delay.h>

 

void ADC_init(void);

unsigned int ADC_read(unsigned char);

 

// ------------------------------------------------

int main(void)

{

unsigned int value;

DDRB=0xFF;                //포트B를 모두 출력으로 지정 (LED출력)

DDRD=0x03;                //0b00000011 으로 포트D의 0,1포트

ADC_init();             // Initialization of ADC

// ch=0;

while(1)

{

value=ADC_read(0);     //ADC0의 40번 핀을 ADC로 지정.......8비트resolution의 값

PORTB=value;                    //이값을 8비트의 LED출력으로 보낸다.

_delay_ms(500);

}

}

//------------------------------------------------

 

void ADC_init(void) // Initialization of ADC

{

ADMUX=(1<<REFS0); // AVcc with external capacitor at AREF

//http://www.engineersgarage.com/sites/default/files/imagecache/Original/wysiwyg_imageupload/1/ADMUX.JPG

//ADMUX::REFS1 REFS0 ADLAR MUX4 MUX3 MUX2 MUX1 MUX0

//Vref is equal to AVcc

//ADC0 채널을 이용

ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);

// Enable ADC and set Prescaler division factor as 128

//http://www.engineersgarage.com/sites/default/files/imagecache/Original/wysiwyg_imageupload/1/ADCSRA.JPG

//ADCSRA::ADEN ADSC ADATE ADIF ADIE ADPS2 ADPS1 ADPS0

//ADEN은 필수로 Set, 나머지 비트는 Prescale따라서 조정 (128이 최고치)

}

 

unsigned int ADC_read(unsigned char ch)

{

ch= ch & 0b00000111; // channel must be b/w 0 to 7

ADMUX |= ch; // selecting channel

     

ADCSRA|=(1<<ADSC); // start conversion

while(!(ADCSRA & (1<<ADIF))); // waiting for ADIF, conversion complete

ADCSRA|=(1<<ADIF); // clearing of ADIF, it is done by writing 1 to it

 

return (ADC);

}