ISCET Digital Systems & Microprocessors 4 — Questions and Answers
Question 1: What is the output of a tri-state buffer when its enable input is deasserted?
- Logic HIGH
- Logic LOW
- High impedance (Hi-Z) (Correct answer)
- Oscillating between HIGH and LOW
Correct answer: High impedance (Hi-Z)
When disabled, a tri-state buffer places its output in a high-impedance state, effectively disconnecting it from the bus.
Question 2: In a synchronous counter, what distinguishes it from an asynchronous (ripple) counter?
- All flip-flops are clocked simultaneously (Correct answer)
- Each flip-flop is triggered by the output of the previous stage
- It counts in Gray code only
- It uses SR flip-flops exclusively
Correct answer: All flip-flops are clocked simultaneously
In a synchronous counter, all flip-flops share the same clock signal and change state simultaneously, eliminating ripple delay.
Question 3: Which microprocessor bus carries the memory location or I/O port being accessed?
- Data bus
- Control bus
- Address bus (Correct answer)
- Power bus
Correct answer: Address bus
The address bus carries the binary address output by the CPU to select a specific memory location or I/O device.
Question 4: What is the Boolean expression for a 2-input XNOR gate?
- A⊕B
- AB + A'B' (Correct answer)
- A'B + AB'
- A+B
Correct answer: AB + A'B'
An XNOR gate outputs HIGH when both inputs are equal: AB + A'B' (both HIGH or both LOW).
Question 5: In a microprocessor's pipeline architecture, what is a 'pipeline stall' (bubble)?
- A clock cycle wasted because the pipeline cannot proceed (Correct answer)
- An overflow in the instruction register
- A fetch from an incorrect memory address
- A hardware reset triggered by the ALU
Correct answer: A clock cycle wasted because the pipeline cannot proceed
A pipeline stall (bubble) occurs when a stage cannot complete its task in one clock cycle, forcing downstream stages to wait and wasting cycles.
Question 6: How many bytes of storage does a memory with a 16-bit address bus provide (assuming byte-addressable)?
- 16KB
- 32KB
- 64KB (Correct answer)
- 128KB
Correct answer: 64KB
A 16-bit address bus can address 2¹⁶ = 65,536 unique locations, which equals 64KB of byte-addressable memory.
Question 7: What is the primary advantage of using BCD (Binary Coded Decimal) representation?
- It requires fewer bits than standard binary
- It simplifies interface with decimal display devices (Correct answer)
- It eliminates the need for an ALU
- It provides error-correcting capability
Correct answer: It simplifies interface with decimal display devices
BCD represents each decimal digit with a 4-bit binary group, making it straightforward to drive seven-segment displays and other decimal I/O devices.
ISCET Digital Systems & Microprocessors 4
What is the output of a tri-state buffer when its enable input is deasserted?