ISCET Digital Systems & Microprocessors 5 — Questions and Answers
Question 1: In a RISC (Reduced Instruction Set Computer) architecture, which characteristic distinguishes it from CISC?
- Instructions take variable numbers of clock cycles
- A large number of complex instructions are available
- Most instructions execute in a single clock cycle (Correct answer)
- Memory operands can be used directly in arithmetic instructions
Correct answer: Most instructions execute in a single clock cycle
RISC architectures use simple, fixed-length instructions designed to execute in a single clock cycle, relying on a load/store model for memory access.
Question 2: What type of memory is used for the BIOS in a PC and retains its contents without power?
- DRAM
- SRAM
- Flash ROM (Correct answer)
- Cache
Correct answer: Flash ROM
Flash ROM (a type of non-volatile memory) stores the BIOS/UEFI firmware and retains data without power while still being electrically erasable and reprogrammable.
Question 3: Which logic operation is equivalent to finding the complement of the sum of two binary numbers' inputs?
- AND
- OR
- NOR (Correct answer)
- NAND
Correct answer: NOR
A NOR gate produces the complement of the OR function: output is HIGH only when ALL inputs are LOW.
Question 4: In a microprocessor system, what is 'memory-mapped I/O'?
- I/O devices that use the same address space as memory (Correct answer)
- A DMA channel dedicated to I/O transfers
- Memory that is physically located on a peripheral card
- A technique for compressing data before storing it
Correct answer: I/O devices that use the same address space as memory
Memory-mapped I/O assigns I/O device registers addresses within the CPU's memory address space, allowing them to be accessed with standard memory read/write instructions.
Question 5: What is the purpose of a multiplexer (MUX) in digital systems?
- To convert serial data to parallel data
- To select one of several input signals and route it to a single output (Correct answer)
- To increase the voltage level of digital signals
- To store multiple bits of data simultaneously
Correct answer: To select one of several input signals and route it to a single output
A multiplexer selects one of its N data inputs based on the binary value of its select lines and routes it to the single output.
Question 6: In signed binary arithmetic using two's complement, what condition indicates overflow when adding two positive numbers?
- The carry-out from bit 0 is 1
- The result's MSB (sign bit) is 1 (Correct answer)
- The carry-out equals the carry-in to the MSB
- The result has more bits than the operands
Correct answer: The result's MSB (sign bit) is 1
Adding two positive numbers (MSB=0) that produce a result with MSB=1 indicates overflow, as the result is incorrectly interpreted as negative.
Question 7: What is the function of a watchdog timer in an embedded microprocessor system?
- Measures the execution time of individual instructions
- Resets the system if the software fails to periodically service it (Correct answer)
- Provides a real-time clock for time-stamping events
- Monitors the power supply voltage level
Correct answer: Resets the system if the software fails to periodically service it
A watchdog timer resets the processor if the running program fails to periodically 'kick' it within a set interval, recovering from software lockups.
ISCET Digital Systems & Microprocessors 5
In a RISC (Reduced Instruction Set Computer) architecture, which characteristic distinguishes it from CISC?