B CompE Bachelor of Computer Engineering Digital Logic Design 1 — Questions and Answers
Question 1: What is the output of an AND gate when both inputs are 1?
- 0
- 1 (Correct answer)
- Undefined
- Depends on voltage
Correct answer: 1
An AND gate outputs 1 (HIGH) only when all of its inputs are 1; with both inputs at 1, the output is 1.
Question 2: Which Boolean expression represents De Morgan's first theorem?
- (A·B)' = A'·B'
- (A+B)' = A'·B'
- (A·B)' = A'+B' (Correct answer)
- (A+B)' = A'+B'
Correct answer: (A·B)' = A'+B'
De Morgan's first theorem states that the complement of a product (NAND) equals the sum of the complements: (A·B)' = A' + B'.
Question 3: How many bits are in one hexadecimal digit?
- 2
- 4 (Correct answer)
- 8
- 16
Correct answer: 4
One hexadecimal digit represents exactly 4 bits, since hex uses base 16 and 2^4 = 16 possible values (0–F).
Question 4: What is the 2's complement representation of -5 in an 8-bit system?
- 11111010
- 10000101
- 11111011 (Correct answer)
- 00000101
Correct answer: 11111011
To find 2's complement of -5: 5 = 00000101, invert to get 11111010, then add 1 to get 11111011.
Question 5: Which logic gate produces an output of 1 only when the number of 1 inputs is odd?
- OR gate
- AND gate
- XNOR gate
- XOR gate (Correct answer)
Correct answer: XOR gate
An XOR (exclusive OR) gate outputs 1 when an odd number of its inputs are 1, making it useful in parity checking and addition circuits.
Question 6: What is the purpose of a Karnaugh Map (K-Map)?
- To simulate digital circuits visually
- To simplify Boolean expressions by grouping minterms (Correct answer)
- To convert decimal numbers to binary
- To design sequential logic circuits
Correct answer: To simplify Boolean expressions by grouping minterms
A Karnaugh Map is a graphical method for simplifying Boolean expressions by visually grouping adjacent minterms to minimize the number of logic gates needed.
B CompE Bachelor of Computer Engineering Digital Logic Design 1
What is the output of an AND gate when both inputs are 1?