Analog-to-Digital Converter (ADC)

The ADC (Analog-to-Digital Converter) is a crucial component in embedded systems, allowing the conversion of analog signals into digital values that can be processed by the microcontroller. The TM4C123 microcontroller features a 12-bit ADC with multiple channels, enabling it to read various analog inputs.

Examples

Polling ADC

#include "TM4C123.h"
#include <stdio.h>

volatile unsigned int adc_value;

int main(void)
{

    /* Enable Clock to ADC0 and GPIO pins*/
    SYSCTL->RCGCGPIO |= (1 << 4); /* Enable Clock to GPIOE or PE3/AN0 */
    SYSCTL->RCGCADC |= (1 << 0);  /* AD0 clock enable*/

    /* initialize PE3 for AIN0 input  */
    GPIOE->AFSEL |= (1 << 3); /* enable alternate function */
    GPIOE->DEN &= ~(1 << 3);  /* disable digital function */
    GPIOE->AMSEL |= (1 << 3); /* enable analog function */

    /* initialize sample sequencer3 */
    ADC0->ACTSS &= ~(1 << 3);            /* disable SS3 during configuration */
    ADC0->EMUX &= ~0xF000;               /* software trigger conversion */
    ADC0->SSMUX3 = 0;                    /* get input from channel 0 */
    ADC0->SSCTL3 |= (1 << 1) | (1 << 2); /* take one sample at a time, set flag at 1st sample */
    ADC0->ACTSS |= (1 << 3);             /* enable ADC0 sequencer 3 */

    /*Iniitialize PF3 as a digital output pin */

    SYSCTL->RCGCGPIO |= 0x20; // turn on bus clock for GPIOF
    GPIOF->DIR |= 0x08;       // set GREEN pin as a digital output pin
    GPIOF->DEN |= 0x08;       // Enable PF3 pin as a digital pin

    while (1)
    {

        ADC0->PSSI |= (1 << 3); /* Enable SS3 conversion or start sampling data from AN0 */
        while ((ADC0->RIS & 8) == 0)
            ;                      /* Wait untill sample conversion completed*/
        adc_value = ADC0->SSFIFO3; /* read adc coversion result from SS3 FIFO*/
        ADC0->ISC = 8;             /* clear coversion clear flag bit*/

        if (adc_value >= 2048)
            GPIOF->DATA = 0x08; /* turn on green LED*/
        else if (adc_value < 2048)
            GPIOF->DATA = 0x00; /* turn off green LED*/
    }
}

Interrupt-Driven ADC

#include "TM4C123.h"
#include <stdio.h>

// Functions Declaration
void delayUs(int); // Delay in Micro Seconds
volatile unsigned int adc_value;

void ADC0SS3_Handler(void)
{
    adc_value = ADC0->SSFIFO3; /* read adc coversion result from SS3 FIFO*/

    if (adc_value >= 2048)
        GPIOF->DATA = 0x08; /* turn on green LED*/
    else if (adc_value < 2048)
        GPIOF->DATA = 0x00; /* turn off green LED*/
    ADC0->ISC = 8;          /* clear coversion clear flag bit*/
    ADC0->PSSI |= (1 << 3); /* Enable SS3 conversion or start sampling data from AN0 */
}

int main(void)
{

    /* Enable Clock to ADC0 and GPIO pins*/
    SYSCTL->RCGCGPIO |= (1 << 4); /* Enable Clock to GPIOE or PE3/AN0 */
    SYSCTL->RCGCADC |= (1 << 0);  /* AD0 clock enable*/

    /* initialize PE3 for AIN0 input  */
    GPIOE->AFSEL |= (1 << 3); /* enable alternate function */
    GPIOE->DEN &= ~(1 << 3);  /* disable digital function */
    GPIOE->AMSEL |= (1 << 3); /* enable analog function */

    /* initialize sample sequencer3 */
    ADC0->ACTSS &= ~(1 << 3);            /* disable SS3 during configuration */
    ADC0->EMUX &= ~0xF000;               /* software trigger conversion */
    ADC0->SSMUX3 = 0;                    /* get input from channel 0 */
    ADC0->SSCTL3 |= (1 << 1) | (1 << 2); /* take one sample at a time, set flag at 1st sample */
    ADC0->ACTSS |= (1 << 3);             /* enable ADC0 sequencer 3 */

    /*Iniitialize PF3 as a digital output pin */

    SYSCTL->RCGCGPIO |= 0x20; // turn on bus clock for GPIOF
    GPIOF->DIR |= 0x08;       // set GREEN pin as a digital output pin
    GPIOF->DEN |= 0x08;       // Enable PF3 pin as a digital pin

    /* Enable ADC Interrupt */
    ADC0->IM |= (1 << 3);        /* Unmask ADC0 sequence 3 interrupt*/
    NVIC->ISER[0] |= 0x00020000; /* enable IRQ17 for ADC0SS3*/
    ADC0->ACTSS |= (1 << 3);     /* enable ADC0 sequencer 3 */
    ADC0->PSSI |= (1 << 3);      /* Enable SS3 conversion or start sampling data from AN0 */

    while (1)
    {
    }
}

Lab Work

1- Modify the code in part (1) above, so that a RED led is on only when the value is greater than 1000. The GREEN led is on only when the value is below 1000.

2- Modify the code above (ADC with interrupt), so the input value and the voltage value are both displayed on the LCD as follow:

ADC: 767
Voltage: 2.474