Code: /*
* automation_of_restaurant_menu_ordering.c
*
* Created: 6/16/2016 11:40:10 AM
* Author: Anusha
*/

#include <util/delay.h>
#include <avr/io.h>

#define Rows PORTC //Pc0,pc1,pc2,pc3
#define Columns PIND //PD4,PD5,PD6

unsigned char upperNibble, keyCode, keyPressed,k,c[6];

char press_key()
{
unsigned char i;
DDRC = 0x0f;
PORTC=0x0f;
PORTD = 0xf0;
k=1;
while(k==1)
{

upperNibble = 0xff;

for(i=0; i<4; i++)
{
_delay_ms(1);
Rows = ~(0x01 << i);
_delay_ms(1);
upperNibble = Columns| 0x0f;

if (upperNibble != 0xff)
{
_delay_ms(20); //key debouncing delay
upperNibble = Columns | 0x0f;
if(upperNibble == 0xff) goto OUT;

keyCode = (upperNibble & 0xf0) | (0x0f & ~(0x01 << i));

while (upperNibble != 0xff)
upperNibble = Columns | 0x0f;

_delay_ms(20); //key debouncing delay

switch (keyCode)
{
case (0xee): keyPressed = '1';k=0;
break;
case (0xed): keyPressed = '4';k=0;
break;
case (0xeb): keyPressed = '7';k=0;
break;
case (0xe7): keyPressed = '*';k=0;
break;
case (0xde): keyPressed = '2';k=0;
break;
case (0xdd): keyPressed = '5';k=0;
break;
case (0xdb): keyPressed = '8';k=0;
break;
case (0xd7): keyPressed = '0';k=0;
break;
case (0xbe): keyPressed = '3';k=0;
break;
case (0xbd): keyPressed = '6';k=0;
break;
case (0xbb): keyPressed = '9';k=0;
break;
case (0xb7): keyPressed = '#';k=0;
break;
case (0x7e): keyPressed = '/';k=0;
break;
case (0x7d): keyPressed = 'X';k=0;
break;
case (0x7b): keyPressed = '-';k=0;
break;
case (0x77): keyPressed = '+';k=0;
break;
default : keyPressed = 'X';k=0;
}
OUT:;
}
}

}
return keyPressed;
}

void uart_init()
{

UCSRC=(1<<URSEL)|(1<<UCSZ1)|(1<<UCSZ0);

UCSRB=(1<<RXEN)|(1<<TXEN);

UBRRL=0x33; // baud rate(51 for 9600)
}

void tx_data(unsigned char c)
{

UDR=c;
while(!(UCSRA & (1<<TXC)));
UCSRA=(1<<TXC);
}

unsigned char rx_data()
{

while ( !(UCSRA & (1<<RXC)) );
UCSRA=(0<<RXC);
return UDR;
}

void Tx_String(unsigned char *str)
{
while(*str)
{
tx_data(*str);
str++;
_delay_ms(100);
}

}

int main(void)
{
uart_init();
unsigned char x,y[4];

int i,j=0;
_delay_ms(100);

while(1)
{
x=press_key();

if((x)!='#')
{

y[j]=x;
++j;

}
else if(x=='#')
{

for (i=0;i<3;i++)
tx_data(y[i]);
_delay_ms(10);

}

}
}