MSP430G2553 - Toggle LED with a switch

In this post, we'll learn to use a switch to toggle an LED using MSP430G2553 μcontroller.

The LED and switch are connected to Port 1, pin 0 and pin 3 respectively. Clicking the switch generates an interrupt. Initially, the LED is in OFF state, if the switch is pressed, the LED starts blinking till next interrupt occurrence/switch press.

If pull mode is enabled by setting PxREN register then either the pull up or pull down option can be selected by setting or clearing the corresponding bit in PxOUT register. One can either select high to low or low to high transition as the trigger for interrupt by setting/clearing the corresponding bit in PxIES register. Detailed information regarding the port settings can be found in the datasheet.
The state of the switch is tracked by a variable named "blink".

Do check the demonstration video: MSP430 with a switch and an LED

#include<msp430.h>

unsigned int blink = 0;

void main(void)

{

 WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer

 P1DIR |= BIT0; // Set P1.0 to output direction

 P1OUT &= ~BIT0; //clear pin

 P1REN |= BIT3; //enable pull mode 

 P1OUT |= BIT3; //pull up

 P1IES |= BIT3; //triggers when button pressed, high to low 

 P1IE |= BIT3; //enable interrupt 

__enable_interrupt(); //global/general interrupts enabled
for(;;) 

 { 

if (blink > 0)
{
P1OUT ^= BIT0; //toggle LED
__delay_cycles(100000); //delay of 10000 cycles at 1MHz
  }

 }
}
//Port 1 Interrupt Service Routine

#pragma vector = PORT1_VECTOR

__interrupt void Port_1(void)
{
blink ^= 0x01;
P1IFG &= ~BIT3; // P1.3 interrupt flag cleared
P1OUT &= ~BIT0; // clear LED to start in off state
}