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CSE/EEE 120 LABS 1–4 COMPREHENSIVE
EXAMINATION REVIEW: STUDY GUIDE |
LATEST UPDATE 2026/2027 | PRACTICE
QUESTIONS AND ANSWERS | EXAM REVIEW.
TABLE OF CONTENTS
I. Lab 1: Half Adder, Full Adder, 4-bit Incrementer and Adder
II. Lab 2: Multiplexers, Decoders and the Arithmetic Logic Unit
III. Lab 3: Advanced ALU Operations and Circuit Testing
IV. Lab 4: The Complete Microprocessor
V. Digital Logic Fundamentals and Circuit Constraints
VI. Binary Number Systems, Arithmetic, and Codes
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question 1: What is the primary function of a half adder?
Correct Answer: To add two single-bit binary numbers and produce a sum and a carry
output.
A half adder is the fundamental building block for binary addition. It has two inputs (A and
B) and two outputs: Sum (A XOR B) and Carry (A AND B). It cannot handle a carry input,
which is why a full adder is needed for multi-bit addition.
question 2: What is the Boolean expression for the Sum output of a half adder?
Correct Answer: Sum = A ⊕ B
The Sum output is the XOR of the two inputs. This is because the sum is 1 only when exactly
one of the inputs is 1. The Carry output is A AND B, which is 1 only when both inputs are 1.
question 3: What is the Boolean expression for the Carry output of a half adder?
Correct Answer: Carry = A · B
The Carry output is the AND of the two inputs. A carry is generated only when both input bits
are 1. This represents the overflow into the next bit position in binary addition.
question 4: How many input combinations does a half adder truth table have?
Correct Answer: 4
A half adder has two inputs, so the truth table has 2² = 4 rows. The combinations are 00, 01,
10, and 11. For each combination, the Sum and Carry outputs are specified.
question 5: What is the output of a half adder when both inputs are 1?
Correct Answer: Sum = 0, Carry = 1
When both inputs are 1, the sum of 1 + 1 = 10 in binary. The Sum bit is 0 and the Carry bit is
1. This is the only combination that produces a carry output in a half adder.
question 6: What is the primary function of a full adder?
Correct Answer: To add three single-bit binary numbers (two data bits and a carry-in)
and produce a sum and a carry-out.
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A full adder extends the half adder by including a carry-in input. This allows multiple full
adders to be cascaded to add multi-bit numbers. The full adder has three inputs (A, B, Cin)
and two outputs (Sum, Cout).
question 7: What is the Boolean expression for the Sum output of a full adder?
Correct Answer: Sum = A ⊕ B ⊕ Cin
The Sum output is the XOR of all three inputs. This produces a 1 when an odd number of
inputs are 1. This is the fundamental property of binary addition with carry propagation.
question 8: What is the Boolean expression for the Carry-out of a full adder?
Correct Answer: Cout = (A · B) + (Cin · (A ⊕ B))
The Carry-out is 1 when at least two of the three inputs are 1. This can be expressed as the
majority function. An alternative form is Cout = (A · B) + (B · Cin) + (A · Cin).
question 9: How many input combinations does a full adder truth table have?
Correct Answer: 8
A full adder has three inputs, so the truth table has 2³ = 8 rows. The combinations range from
000 to 111. For each combination, the Sum and Carry-out outputs are specified.
question 10: What is the output of a full adder when A = 1, B = 1, and Cin = 1?
Correct Answer: Sum = 1, Cout = 1
When all three inputs are 1, the sum is 1 + 1 + 1 = 11 in binary. The Sum bit is 1 and the
Carry-out bit is 1. This represents the maximum output of a full adder.
question 11: How can a full adder be constructed from two half adders?
Correct Answer: Connect the Sum of the first half adder to one input of the second half
adder, with Cin as the other input; the final Sum is the Sum of the second half adder,
and Cout is the OR of the two carry outputs.
The first half adder adds A and B, producing an intermediate sum and carry. The second half
adder adds the intermediate sum with Cin. The final carry-out is the OR of the two carry
outputs because a carry is generated if either stage produces one.
question 12: What is a 4-bit ripple-carry adder?
CSE/EEE 120 LABS 1–4 COMPREHENSIVE
EXAMINATION REVIEW: STUDY GUIDE |
LATEST UPDATE 2026/2027 | PRACTICE
QUESTIONS AND ANSWERS | EXAM REVIEW.
TABLE OF CONTENTS
I. Lab 1: Half Adder, Full Adder, 4-bit Incrementer and Adder
II. Lab 2: Multiplexers, Decoders and the Arithmetic Logic Unit
III. Lab 3: Advanced ALU Operations and Circuit Testing
IV. Lab 4: The Complete Microprocessor
V. Digital Logic Fundamentals and Circuit Constraints
VI. Binary Number Systems, Arithmetic, and Codes
,2|Page
question 1: What is the primary function of a half adder?
Correct Answer: To add two single-bit binary numbers and produce a sum and a carry
output.
A half adder is the fundamental building block for binary addition. It has two inputs (A and
B) and two outputs: Sum (A XOR B) and Carry (A AND B). It cannot handle a carry input,
which is why a full adder is needed for multi-bit addition.
question 2: What is the Boolean expression for the Sum output of a half adder?
Correct Answer: Sum = A ⊕ B
The Sum output is the XOR of the two inputs. This is because the sum is 1 only when exactly
one of the inputs is 1. The Carry output is A AND B, which is 1 only when both inputs are 1.
question 3: What is the Boolean expression for the Carry output of a half adder?
Correct Answer: Carry = A · B
The Carry output is the AND of the two inputs. A carry is generated only when both input bits
are 1. This represents the overflow into the next bit position in binary addition.
question 4: How many input combinations does a half adder truth table have?
Correct Answer: 4
A half adder has two inputs, so the truth table has 2² = 4 rows. The combinations are 00, 01,
10, and 11. For each combination, the Sum and Carry outputs are specified.
question 5: What is the output of a half adder when both inputs are 1?
Correct Answer: Sum = 0, Carry = 1
When both inputs are 1, the sum of 1 + 1 = 10 in binary. The Sum bit is 0 and the Carry bit is
1. This is the only combination that produces a carry output in a half adder.
question 6: What is the primary function of a full adder?
Correct Answer: To add three single-bit binary numbers (two data bits and a carry-in)
and produce a sum and a carry-out.
, 3|Page
A full adder extends the half adder by including a carry-in input. This allows multiple full
adders to be cascaded to add multi-bit numbers. The full adder has three inputs (A, B, Cin)
and two outputs (Sum, Cout).
question 7: What is the Boolean expression for the Sum output of a full adder?
Correct Answer: Sum = A ⊕ B ⊕ Cin
The Sum output is the XOR of all three inputs. This produces a 1 when an odd number of
inputs are 1. This is the fundamental property of binary addition with carry propagation.
question 8: What is the Boolean expression for the Carry-out of a full adder?
Correct Answer: Cout = (A · B) + (Cin · (A ⊕ B))
The Carry-out is 1 when at least two of the three inputs are 1. This can be expressed as the
majority function. An alternative form is Cout = (A · B) + (B · Cin) + (A · Cin).
question 9: How many input combinations does a full adder truth table have?
Correct Answer: 8
A full adder has three inputs, so the truth table has 2³ = 8 rows. The combinations range from
000 to 111. For each combination, the Sum and Carry-out outputs are specified.
question 10: What is the output of a full adder when A = 1, B = 1, and Cin = 1?
Correct Answer: Sum = 1, Cout = 1
When all three inputs are 1, the sum is 1 + 1 + 1 = 11 in binary. The Sum bit is 1 and the
Carry-out bit is 1. This represents the maximum output of a full adder.
question 11: How can a full adder be constructed from two half adders?
Correct Answer: Connect the Sum of the first half adder to one input of the second half
adder, with Cin as the other input; the final Sum is the Sum of the second half adder,
and Cout is the OR of the two carry outputs.
The first half adder adds A and B, producing an intermediate sum and carry. The second half
adder adds the intermediate sum with Cin. The final carry-out is the OR of the two carry
outputs because a carry is generated if either stage produces one.
question 12: What is a 4-bit ripple-carry adder?
