BEE Digital Logic and Systems 3 — Questions and Answers
Question 1: Which number system uses base 16 and includes digits 0-9 and letters A-F?
- Octal
- Binary
- Hexadecimal (Correct answer)
- BCD
Correct answer: Hexadecimal
Hexadecimal (base-16) uses digits 0–9 and letters A–F to represent values 0–15 in a single digit, commonly used in digital systems.
Question 2: A D flip-flop is triggered on the rising edge of the clock. If D=1 at the rising edge, the next state Q+ is:
- 0
- 1 (Correct answer)
- Same as Q
- Complement of Q
Correct answer: 1
A D flip-flop copies the input D to the output Q on the active clock edge, so Q+ = D = 1.
Question 3: What is the 2's complement representation of -6 using 4 bits?
- 0110
- 1010 (Correct answer)
- 1001
- 1110
Correct answer: 1010
+6 in 4 bits is 0110; inverting gives 1001, adding 1 yields 1010, which is the 2's complement of -6.
Question 4: Which combinational circuit converts a binary code to a one-hot encoded output?
- Multiplexer
- Encoder
- Decoder (Correct answer)
- Priority encoder
Correct answer: Decoder
A decoder takes an n-bit binary input and activates exactly one of 2ⁿ output lines, producing a one-hot (active-high) output.
Question 5: In digital logic, glitches (hazards) in combinational circuits are caused by:
- Incorrect Boolean expressions
- Unequal propagation delays through different paths (Correct answer)
- Too many gate inputs
- Insufficient fan-out
Correct answer: Unequal propagation delays through different paths
Glitches occur when signal transitions take different amounts of time through alternate paths, causing momentary incorrect output values.
Question 6: What is the function of a priority encoder with inputs I0–I3?
- Outputs the binary code of the highest-priority active input (Correct answer)
- Activates one output for each input
- Selects one of many data inputs
- Converts Gray code to binary
Correct answer: Outputs the binary code of the highest-priority active input
A priority encoder resolves simultaneous active inputs by outputting the binary code corresponding to the highest-priority (usually highest-numbered) active input.
Question 7: An SR latch built from NOR gates has an undefined (forbidden) state when:
- S=0, R=0
- S=1, R=0
- S=0, R=1
- S=1, R=1 (Correct answer)
Correct answer: S=1, R=1
When both S=1 and R=1 in a NOR-based SR latch, both outputs are forced to 0, violating the complementary output requirement and creating an undefined next state.
BEE Digital Logic and Systems 3
Which number system uses base 16 and includes digits 0-9 and letters A-F?