//--------------------------------------------------------------
//led_sw1.c  ( version 2013 b)
//exercise: Modied this program so it can run on your new lopc2131 board using the 
// Input:sw3, output :LED (D1)
//
//; Note: LED(D1) is at GPIO P0.10, sw3 is at GPIO P0.20(for EINT3 //ext.interrupt)
//; Note: LED(D2) is at GPIO P0.11, sw4 is at GPIO P0.21
//; Note: LED(D3) is at GPIO P0.12, sw5 is at GPIO P0.22
//; Note: LED(D4) is at GPIO P0.13, sw6 is at GPIO P0.23
//--------------------------------------------------------------
#include <lpc21xx.h> //define IO0PIN ,IO0DIR.. Etc
// see http://www.keil.com/dd/docs/arm/philips/lpc21xx.h
#define RED_LED 0x00400000 //set p0.22 as RED LED
#define SW1	  0x00100000 //set p0.20 as SW1
int  main(void)
{ long tmp;	// variable for temp storage of port 0  status
  IO0DIR = RED_LED;	// set p0.22 as output
    while(1) 
    {   tmp =IO0PIN & SW1;//read SW1(p0.20)depressed=0
       if(tmp==0) // What happens “if (tmp!=0)” is used?
          IO0SET = RED_LED; //if SW1 pressed LED is on
       else IO0CLR = RED_LED;	// otherwise off the LED
    }
 }