BEE Digital Logic and Microprocessors 2 — Questions and Answers
Question 1: Which Boolean expression represents the output of a 2-input XNOR gate?
- A ⊕ B
- A·B + A'·B' (Correct answer)
- A' + B'
- A·B'
Correct answer: A·B + A'·B'
XNOR outputs 1 when both inputs are equal, expressed as A·B + A'·B'.
Question 2: In a JK flip-flop, what happens when both J=1 and K=1 on the active clock edge?
- Output is set to 1
- Output is reset to 0
- Output toggles (Correct answer)
- Output is held unchanged
Correct answer: Output toggles
When J=K=1, the JK flip-flop toggles its output on each active clock edge.
Question 3: A 4-bit ripple carry adder adds two 4-bit numbers. What is the maximum propagation delay if each full adder has a carry propagation delay of 10 ns?
- 10 ns
- 20 ns
- 30 ns
- 40 ns (Correct answer)
Correct answer: 40 ns
In a ripple carry adder, carry propagates through all 4 stages, giving 4 × 10 ns = 40 ns total delay.
Question 4: What is the purpose of the program counter (PC) in a microprocessor?
- Counts the number of executed instructions
- Holds the address of the next instruction to fetch (Correct answer)
- Stores the result of arithmetic operations
- Controls the ALU operation mode
Correct answer: Holds the address of the next instruction to fetch
The program counter holds the memory address of the next instruction to be fetched and executed.
Question 5: Which addressing mode uses the content of a register as the memory address?
- Immediate
- Direct
- Register indirect (Correct answer)
- Indexed
Correct answer: Register indirect
Register indirect addressing uses the value stored in a register as the effective memory address.
Question 6: How many memory locations can be addressed by a microprocessor with a 16-bit address bus?
- 16 KB
- 32 KB
- 64 KB (Correct answer)
- 128 KB
Correct answer: 64 KB
A 16-bit address bus can address 2^16 = 65,536 = 64 K locations.
Question 7: In a Karnaugh map, which grouping size is NOT valid?
- 1
- 2
- 3 (Correct answer)
- 4
Correct answer: 3
K-map groups must be powers of 2 (1, 2, 4, 8, 16...); groups of 3 are invalid.
BEE Digital Logic and Microprocessors 2
Which Boolean expression represents the output of a 2-input XNOR gate?