Source Code:

    

      

      #include <avr/io.h>   

#define F_CPU 16000000UL
#include <util/delay.h>

#define	KEY_PRT  PORTD 		//keyboard PORT
#define	KEY_DDR  DDRD 	
#define	KEY_PIN  PIND 	

unsigned char keypad[4][4] =//{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16};
{'0','1','2','3',
	'4','5','6','7',
	'8','9','A','B',
'C','D','E','F'};
int main(void)
{
	unsigned char colloc, rowloc;

	DDRB = 0xFF;
	KEY_DDR = 0xF0;
	KEY_PRT = 0xFF;

	while(1) 			
	{
		do
		{
			KEY_PRT &= 0x0F;     		
			asm("NOP");
			colloc = (KEY_PIN & 0x0F);	
		} while(colloc != 0x0F);		

		do
		{
			do
			{
				_delay_ms(20);			
				colloc =(KEY_PIN&0x0F);	
			} while(colloc == 0x0F);	
			
			_delay_ms(20);			
			colloc = (KEY_PIN & 0x0F);	
		}while(colloc == 0x0F);		

		while(1)
		{
			KEY_PRT = 0xEF;			
			asm("NOP");
			colloc = (KEY_PIN & 0x0F);	
			if(colloc != 0x0F) 
			{
				rowloc = 0;		
				break;	
			}

			KEY_PRT = 0xDF;			
			asm("NOP");
			colloc = (KEY_PIN & 0x0F);	
			
			if(colloc != 0x0F) 		
			{
				rowloc = 1;			
				break;				
			}

			KEY_PRT =  0xBF;			
			asm("NOP");
			colloc = (KEY_PIN & 0x0F);	
			if(colloc != 0x0F) 		
			{
				rowloc = 2;			
				break;				
			}

			KEY_PRT = 0x7F;			
			asm("NOP");
			colloc = (KEY_PIN & 0x0F);	
			rowloc = 3;				
			break;				
		}

		if(colloc == 0x0E)
		PORTB = (keypad[rowloc][0]);
		else if(colloc == 0x0D)
		PORTB = (keypad[rowloc][1]);
		else if(colloc == 0x0B)
		PORTB = (keypad[rowloc][2]);
		else
		PORTB = (keypad[rowloc][3]);
	}
	return 0;	
}