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Prof. M. Mansour
American University of Beirut
Department of Electrical and Computer Engineering
EECE 320 – Digital Systems Design
Summer
2009
Homework 3
(Due Friday July 17 in class)
Problem 1
[10 pts]
: Design a 4bit adder logic circuit. First design a logic circuit that adds two bits
A
0
and
B
0
and a
carry in
C
in0
, and generates a sum bit
S
0
and an output carry bit
C
out0
. Write the minimized Boolean equations of this
block. Then use this block to design a circuit that adds
A
3
A
2
A
1
A
0
and
B
3
B
2
B
1
B
0
. Show all your connections.
Problem 2
[10 pts]
: Repeat Problem 1, but now for a circuit that
subtracts
two numbers
A
3
A
2
A
1
A
0
and
B
3
B
2
B
1
B
0
.
Hint: Use the relationship between addition and subtraction in 2’s complement.
Problem 3
[10 pts]
: Design a circuit that increments a 4bit number
A
3
A
2
A
1
A
0
by 1. Write logic expressions for all
outputs, and simplify them as much as you can. Start by designing a 1bit incrementor circuit using its truth table.
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