BEE Digital Logic and Microprocessors 5 — Questions and Answers
Question 1: What is the Boolean simplification of the expression AB + AB'?
- A'
- B
- A (Correct answer)
- AB
Correct answer: A
AB + AB' = A(B + B') = A·1 = A by the complement and identity laws.
Question 2: A shift register can be used to perform which arithmetic operation on a binary number?
- Addition
- Multiplication or division by powers of 2 (Correct answer)
- Subtraction
- Modulo operation
Correct answer: Multiplication or division by powers of 2
Shifting left multiplies by 2 and shifting right divides by 2, so shift registers perform multiplication/division by powers of 2.
Question 3: In DMA (Direct Memory Access) data transfer, what role does the CPU play during the transfer?
- The CPU manages each data word transfer
- The CPU is bypassed; the DMA controller handles the transfer (Correct answer)
- The CPU and DMA share alternating bus cycles
- The CPU pre-loads the DMA buffer
Correct answer: The CPU is bypassed; the DMA controller handles the transfer
DMA allows the DMA controller to transfer data directly between memory and I/O without CPU intervention, freeing the CPU for other tasks.
Question 4: Which of the following best describes a tri-state buffer?
- A buffer with three voltage levels
- A device with outputs of logic 0, logic 1, or high-impedance (Correct answer)
- A buffer that operates at three different supply voltages
- A three-input AND gate
Correct answer: A device with outputs of logic 0, logic 1, or high-impedance
A tri-state buffer can output logic 0, logic 1, or a high-impedance (Hi-Z) state that effectively disconnects the output from the bus.
Question 5: In a microprocessor's instruction cycle, which operation follows the fetch phase?
- Write-back
- Decode (Correct answer)
- Execute
- Memory access
Correct answer: Decode
After fetching the instruction from memory, the processor decodes it to determine the operation and operands.
Question 6: How many flip-flops are required to build a 16-state sequential counter?
- 2
- 4 (Correct answer)
- 8
- 16
Correct answer: 4
n flip-flops can represent 2^n states; 2^4 = 16, so 4 flip-flops are needed for a 16-state counter.
Question 7: What is the primary function of the stack pointer (SP) register in a microprocessor?
- Points to the top of the call stack in memory (Correct answer)
- Holds the return address of the current subroutine
- Counts the number of active subroutine calls
- Stores temporary arithmetic results
Correct answer: Points to the top of the call stack in memory
The stack pointer register contains the memory address of the top of the stack, updated automatically on push and pop operations.
BEE Digital Logic and Microprocessors 5
What is the Boolean simplification of the expression AB + AB'?