AVRFreaks.net

adc0=0
adc1=10
adc2=20
adc3=30
First time read adc0 and sends 0
Second time reads adc1 sends 10
Third time reads adc2 sends 20
Fourth time reads adc3 sends 30
Fifth time reads adc0 sends 30
Six time reads adc1 sends 30

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#define USART_BAUDRATE 9600
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)


   //adc~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
void InitADC()
{

ADMUX=(0<<REFS0)|(0<<REFS1);                       
ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(0<<ADPS0);
}

uint16_t ReadADC(uint8_t ch)
{
   //Select ADC Channel ch must be 0-7
   ch=ch&0b00000111;
   ADMUX|=ch;

   //Start Single conversion
   ADCSRA|=(1<<ADSC);

   //Wait for conversion to complete
   while(!(ADCSRA & (1<<ADIF)));

 

   ADCSRA|=(1<<ADIF);

   return(ADC);
   
}


//-----------------------MAIN
int main (void)
{
//serialINSTAL
 UCSRB |= (1 << RXEN) | (1 << TXEN);   
   UCSRC |= (1 << URSEL) | (1 << UCSZ0) | (1 << UCSZ1);

   UBRRL = BAUD_PRESCALE;
   UBRRH = (BAUD_PRESCALE >> 8);
//ENDserialINSTAL


uint16_t adc_result;
InitADC();
 
char a;


begin:

while ((UCSRA & (1 << RXC)) == 0) {}; // Do nothing until read serial
a=UDR;


if(a==((char) '1')){
adc_result=ReadADC(0);
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}


if(a==((char) '2')){
adc_result=ReadADC(1);                 
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

if(a==((char) '3')){
adc_result=ReadADC(2);                 
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

if(a==((char) '4')){
adc_result=ReadADC(3);                 
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

if(a==((char) '5')){
adc_result=ReadADC(4);                   
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

if(a==((char) '6')){
adc_result=ReadADC(5);                 
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

if(a==((char) '7')){
adc_result=ReadADC(6);                   
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

if(a==((char) '8')){
adc_result=ReadADC(7);                   
while ((UCSRA & (1 << UDRE)) == 0) {};
UDR=adc_result;
goto begin;
}

goto begin;
}

first clear the old channel
ADMUX &= 0b11111000

then OR the new one
ADMUX |= ch;

// define reference
#define REF (1<<REFS0)|(1<<REFS1)

// set/change channel
ADMUX = REF | channel