MSP430FR4133: Issues reading from A9 ADC pin

You don't want the return in there, that will return from main and goes who knows where.

You also don't want PXOUT &= BIT0.

If bit 0 is on:

0x01 & 0x01 == 0x01

if bit 0 is off:

0x000 & 0x01 =  0x00

So your statement will leave bit 0 unchanged.

You want PXOUT &= (~BIT0) which will set bit 0 to 0 and leave the others unchanged.

If you are new to C, here are a list of bit manipulations:

https://c-faq.com/misc/bitmanip.html

Thanks for your help, Keith. I managed to get the LEDs on P1.0 and 4.0 to respond to a voltage input. However, when I use the 3.3V MSP output as an input to the A9 pin, the P4.0 LED won't respond. When I swap the conditions around such that I want the P1.0 LED to light when an input exceeds the threshold voltage, the P1.0 LED will turn on when the 3.3V source is suppled but the P4.0 will remain on. 

I think you need to show the new code.

3.3 V should always result in a 4096 code. Have you tried to use the debugger to see what you get in ADC_Value?

Also, it can't hurt to make ADC_Value volatile, either

I have attached the new code. When using the debugger to see what ADC_value is I get the following error. Thank you.

#include <msp430.h>
#include <driverlib.h>

volatile unsigned int ADC_value;

int main(void){

WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer

P1DIR |= BIT0; // setting pins to output
P4DIR |= BIT0;

PMM_unlockLPM5();

//*choose analog function for pins*

//ADC setup
SYSCFG2 |= ADCPCTL9;

ADCCTL0 |= ADCON; // TURN ON ADC
ADCCTL1 |= ADCSHP; //sampling signal source = sampling timer
ADCCTL1 |= ADCSSEL_2; // choose SMCLK
ADCCTL2 |= ADCRES_2; // 12 bit resolution
ADCMCTL0 |= ADCSREF_7;
ADCMCTL0 |= ADCINCH_9; // A9 as input

ADCIFG &= ~0x01; //clearing interrupt flag

while(1){

ADCCTL0 |= ADCENC | ADCSC; //enable and start conversion

while( (ADCIFG & ADCIFG0) == 0 );

ADC_value = ADCMEM0;

if (ADC_value > 500) {

P1OUT &= ~BIT0;
P4OUT |= BIT0;

} else {

P1OUT |= BIT0;
P4OUT &= ~BIT0;

}
}
}

Please use code tags to post code.

This works fine for me on an MSP-EXP430FR2311, including letting me examine the value of ADC_Result.

You might turn optimization off for an example like this.

#include <msp430.h>

volatile unsigned int ADC_Result;

int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;                                // Stop WDT

    // Configure GPIO
    P1DIR |= BIT0;                                           // Set P1.0/LED to output direction
    P1OUT &= ~BIT0;                                          // P1.0 LED off
    
    P2DIR |= BIT0;
    P2OUT &= ~BIT0;

    // Configure ADC A1 pin
    P1SEL0 |= BIT1;
    P1SEL1 |= BIT1;

    // Disable the GPIO power-on default high-impedance mode to activate
    // previously configured port settings
    PM5CTL0 &= ~LOCKLPM5;

    // Configure ADC10
    ADCCTL0 |= ADCSHT_2 | ADCON;                             // ADCON, S&H=16 ADC clks
    ADCCTL1 |= ADCSHP;                                       // ADCCLK = MODOSC; sampling timer
    ADCCTL2 |= ADCRES;                                       // 10-bit conversion results
    ADCMCTL0 |= ADCINCH_1;                                   // A1 ADC input select; Vref=AVCC
    //ADCIE |= ADCIE0;                                         // Enable ADC conv complete interrupt
  
    while(1)
    {
        ADCCTL0 |= ADCENC | ADCSC;                           // Sampling and conversion start

        while( (ADCIFG & ADCIFG0) == 0 );

        ADC_Result = ADCMEM0;

        __no_operation();                                    // For debug only
        if (ADC_Result < 0x1FF)
        {
            P1OUT &= ~BIT0;
            P2OUT |= BIT0;
        }
        else
        {
            P1OUT |= BIT0;                                   // Set P1.0 LED on
            P2OUT &= ~BIT0;
        }
        __delay_cycles(5000);
    }
}

You need to set a breakpoint to read a variable value Liam. Double click the left margin then when it hits this point and pauses you can see the value.