Write the simple switch and LED interfacing code in Embedded C on KL25Z FRDM board.

// In this experiment single switch taken from the 16 switches of 4X4 matrix keypad

//4 columns are connected to the 4-7 as I/P and 4 rows are connected to the 0-3 as O/P pins of the //PORTC

// blue LED connected on the PORTD pin1, will lit whenever configured switch is pressed

#include <MKL25Z4.H>

//user define function to provide a delay in micro second
void delayUs(int n);

//function to detect the switch
char Switch_detect(void);

int main(void)
{
    SIM->SCGC5 |= 0x1800;       /* enable clock to Port C and D  */
        
        //initialization switch 1 from matrix keypad
        // PTC0 and PTC4
        PORTC->PCR[0] = 0x103;      /* make PTC0 pin as GPIO and enable pullup*/
        PORTC->PCR[4] = 0x103;      /* make PTC4 pin as GPIO and enable pullup*/
        PTC->PDDR = 0x01;         /* make PTC0 as output pin and PTC4 input pin*/
    
        //PortD pin 1 configure for blue LED
        PORTD->PCR[1] = 0x100;      /* make PTD1 pin as GPIO */
        PTD->PDDR |= 0x02;          /* make PTD1 as output pin */

    while(1)
    {
        if (Switch_detect() != 0)    /* if a key is pressed? */
            PTD->PDOR &= ~0x02;          /* turn on blue LED */
        else
            PTD->PDOR |= 0x02;          /* turn off blue LED */
    }
}

char Switch_detect(void)
{
    int col;

    PTC->PDDR |= 0x01;          /* enable row1 */
    PTC->PDOR &= ~0x01;            /* we make sure it must clear before switch detection  process*/
    delayUs(2);                 /* wait for signal return */
    col = PTC->PDIR & 0x10;     /* read column1 */
    PTC->PDDR = 0;              /* disable row1*/
    if (col == 0x10)
        return 0;               /* no key pressed */
    else
        return 1;               /* a key is pressed */
}

void delayUs(int n)
{
    int i; int j;
    for(i = 0 ; i < n; i++) {
        for(j = 0; j < 8; j++) ;
    }
}