MSP-EXP430FR4133 Button S2

According to the schematic, buttons S1 and S2 are just connections between P1.2/P2.6 and ground. This means that the GPIO pins need pull-up resistors to have a defined state when the button is not pressed. In other words, the PxREN and PxOUT bits must be set.

I don't know why it works without the pull-up for S1, but it's probably just luck. Don't rely on it.

Sammy,

when using buttons, the OUT-register is used in combination with the REN-register to set a pull-up/down-resistor. Can you show your complete code? S1 is on P1.2, S2 on P2.6 - both have no external resistor, so they both need a software set one inside the microcontroller. Since both switches short the pin to GND, you will use a pull-up resistor by setting

P1OUT |= 0x04; // P1.2 resistor pulls-up
P1REN |= 0x04; // P1.2 enable resistor

and

P2OUT |= 0x40; // P2.6 resistor pulls-up
P2REN |= 0x40; // P2.6 enable resistor

Dennis

This is my code for S1:

int main(void) {
    volatile unsigned int p2_in;
    WDTCTL = WDTPW | WDTHOLD;               // Stop watchdog timer
    PM5CTL0 &= ~LOCKLPM5;                   // Disable the GPIO power-on default high-impedance mode
                                            // to activate previously configured port settings

    P1DIR |= BIT0;
    P4DIR |= BIT0;
    P5DIR |= BIT0;

    P1REN |= BIT2;
    P1DIR &= ~BIT2;
    //P1OUT |= BIT2;
    P1SEL0 &= ~BIT2;
    for(;;) {
        volatile unsigned int i;            // volatile to prevent optimization

        P1OUT ^= 0x01;                      // Toggle P1.0 using exclusive-OR
        p2_in = P1IN;
        if ((P1IN & BIT2) == BIT2) {
        	P4OUT |= 0x01;
        } else {
        	P4OUT &= ~0x01;
        }
  
        i = 10000;                          // SW Delay
        do i--;
        while(i != 0);
    }

    return 0;
}

This is my code for S2:

int main(void) {
    volatile unsigned int p2_in;
    WDTCTL = WDTPW | WDTHOLD;               // Stop watchdog timer
    PM5CTL0 &= ~LOCKLPM5;                   // Disable the GPIO power-on default high-impedance mode
                                            // to activate previously configured port settings
    P1DIR |= 0x01;                          // Set P1.0 to output direction
    P4DIR |= 0x01;

    // Initialize Switch 2
    P2REN |= BIT6;							// Initialize port 2.6 enabling pull up register
    P2DIR &= ~BIT6;							// Set P2.6 to be input by clearing that bit
    P2OUT |= BIT6;
    P2SEL0 &= ~BIT6;

    for(;;) {
        volatile unsigned int i;            // volatile to prevent optimization

        P1OUT ^= 0x01;                      // Toggle P1.0 using exclusive-OR
        p2_in = P2IN;
        if ((P2IN & BIT6) == BIT6) {
        	P4OUT |= 0x01;
        } else {
        	P4OUT &= ~0x01;
        }
      
        i = 10000;                          // SW Delay
        do i--;
        while(i != 0);
    }

    return 0;
}