working of diff type of keypad

1. Welcome to
Summer Training Program
2009

2. Keypad

3. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
0
0
0

4. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~1
1
~1

5. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~1
1
~17

6. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~2
2
~2

7. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~2
2
~66

8. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~2
2
~2

9. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~2
2
~18

10. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~4
4
~4

11. 0 1 2 3 4 5 6 7
PORTB
DDRB
PINB
~4
4
~12

12. int key(void){
for(DDRB=1,DDRB>0,DDRB*=2){
PORTB=~DDRB;
_delay_us(10);
if(PINB!=PORTB) return PINB;
}
return 0;
}