7.External interrupt.c

#include<lpc214x.h>

void Extint0_Isr(void) __irq; 			//declaration of ISR

unsigned char int_flag = 0, flag = 0;

int main(void)
{
   	IO1DIR  = 0X02000000;  		  
   	IO1SET  = 0X02000000;
   	PINSEL1	=0X00000001;          		//Setup P0.16 to alternate function EINT0

   	EXTMODE	=0x01;                		//edge i.e falling egge trigger and active low
   	EXTPOLAR= 0X00;
   	VICVectAddr0 = (unsigned long) Extint0_Isr;   //Assign the EINT0 ISR function 
   	VICVectCntl0 = 0x20 | 14;      		//Assign the VIC channel EINT0 to interrupt priority 0
   	VICIntEnable |= 0x00004000;    		//Enable the EINT0 interrupt

	while(1)                            //waiting for interrupt to occur
    {
   		if(int_flag == 0x01)
			 {
					if(flag == 0)
						{
							IO1CLR = 0X02000000;
							flag = 1;
						}
					else if(flag == 1)
						{
							IO1SET = 0x02000000;
							flag = 0;
						}
					int_flag = 0x00;
			}		  
  	}
}

void Extint0_Isr(void)__irq 
{           //whenever there is a low level on EINT0
  EXTINT |= 0x01;                 	//Clear interrupt
	int_flag = 0x01;
	VICVectAddr = 0;					//Acknowledge Interrupt
}