Source Code:

    

      

      #include <avr/io.h>

#define F_CPU 8000000UL
#include <util/delay.h>

#define KEY_PRT 	PORTC
#define KEY_DDR		DDRC
#define KEY_PIN		PINC

unsigned char keypad[4][4] = {{'0','1','2','3'},
{'4','5','6','7'},
{'8','9','A','B'},
{'C','D','E','F'}};

int main ()
{
	unsigned char colloc, rowloc;

	DDRD = 0xFF;

	while(1)
  	{
		while(1)
		{

			KEY_DDR = 0xF0;
			KEY_PRT = 0xFF;

			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);

			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);
			if(colloc != 0x0F)
			{
				rowloc = 3;
				break;
			}
		}

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