Button interrupt with msp430fr5969 microcontroller

Hi folks, I just felt like writing a brief post on the implementation of button interrupt using the MSP430FR5969 Launchpad by Texas Instrument. Detailed information can be found here.

I’ll be using the S2 button (P1.1) as the source of the interrupt. The LED2 (P1.0) turns on/off whenever interrupt occurs. We’ll cater to two use cases in this post.

• When interrupt occur every time the button is pushed and pulled; thus toggling the LED once. The code to achieve that is shown below:

#include <msp430fr5969.h>

#define LED BIT0
#define BUTTON BIT1

void main(void){
  WDTCTL = WDTPW + WDTHOLD;       // Stop watchdog timer
  PM5CTL0 &= ~LOCKLPM5;           //Free or unlock pins from high Impedance

  P1DIR |= LED;                   // Set LED (P1.0) to output direction
  P1OUT &= ~LED;                  // Set LED (P1.0) to output low

  P1REN |= BUTTON;                // Enable P1.1 internal resistance. Use PIREN $= ~BUTTON to turn it off
  P1OUT |= BUTTON;                // Set P1.1 as pull-Up resistance. Use P1OUT $= ~BUTTON for pull-down
  P1IES |= BUTTON;                // P1.1 Interrupt Edge Select Hi/Lo.use P1IES &= ~BUTTON for Lo/Hi
  P1IFG &= ~BUTTON;               // P1.1 IFG cleared
  P1IE |= BUTTON;                 // P1.1 interrupt enabled

  __bis_SR_register(GIE);         // Enable interrupts globally

  while(1) {}
}
// Port 1 interrupt service routine
#pragma vector=PORT1_VECTOR
__interrupt void Port_1(void){
    P1OUT^=LED;                   // Toggle the LED
    P1IFG &= ~BUTTON;             // P1.1 IFG cleared
}

• When interrupt occur every time the button is pushed or pulled; thus toggling the LED on Hi-Lo and Lo-Hi. This can be achieved by appending this line of code to the ISR. P1IES &= ~BIT1; The final ISR should look something like,

  // Port 1 interrupt service routine
  #pragma vector=PORT1_VECTOR
  __interrupt void Port_1(void){
    P1OUT^=LED;                   // Toggle the LED
    P1IFG &= ~BUTTON;             // P1.1 IFG cleared
    P1IES &= ~BIT1;               // P1.1 Lo/Hi edge select
  }
  

NOTE

Pressing the Button too quickly may lead to inconsistent operation due to the bouncing issue with buttons, which can be handled through a process called debouncing. For more information on that see here.