digital electronics

1. Half & Full Subtractor
• Half Subtractor
• Full Subtractor

2. Half- Subtractor
• Function Table
• Expression
• Logic Circuit

3. Half- Subtractor Function Table
Input Output
A B Difference Borrow
0 0 0 0
0 1 1 1
1 0 1 0
1 1 0 0

4. Half- Subtractor Circuit
B
A
B
A
B
A
Difference 


 B
A
Borrow '


5. Full- Subtractor
• Function Table
• Expression
• Logic Circuit

6. Full-Subtractor Function Table
Input Output
A B C Difference Borrow
0 0 0 0 0
0 0 1 1 1
0 1 0 1 1
0 1 1 0 1
1 0 0 1 0
1 0 1 0 0
1 1 0 0 0
1 1 1 1 1

7. Difference Expression
ABC
C
B
A
C
B
A
C
B
A
D 



)
(
)
( BC
C
B
A
C
B
C
B
A
D 



)
(
)
( C
B
A
C
B
A
D 




8. Borrow Expression
ABC
BC
A
BC
A
C
B
A
Borrow 


 '
'
'
'
'
BC
C
A
B
A
Borrow 

 '
'
1
1 1 1

9. Full-Subtractor Circuit
BC
C
A
B
A
Borrow 

 '
'
-Draw the circuit

11. Full-Subtractor based on
Two Half-Subtractors
Full-Subtractor = Half-Subtractor + Half-Subtractor

12. Parallel Binary Subtractor
• Multiple Single bit Full-Subtractr connected in
Parallel

13. 4-bit Parallel Subtractor
1100
0101
____________
0111

14. • A complete logical circuit capable of adding or
subtracting two numbers by using 2’s
complement is shown in Figure below
Binary Adder and
Subtractor