Question 1

8085-style microprocessor basics: In a typical 8-bit microprocessor system (such as Intel 8085 family), how many bits wide is the data bus used for reading/writing data?

Accepted Answer

Introduction / Context: The data bus width indicates how many data bits a processor can transfer in one operation. In classic 8-bit microprocessors (e.g., 8085/6502/Z80), the data bus is central to memory and I/O transfers. This question focuses on identifying the data bus width in such systems. Given Data / Assumptions: Target class: 8-bit microprocessor architecture (e.g., 8085). We refer to external data path width (bus), not internal micro-operations. Standard memory-mapped I/O assumed. Concept / Approach: An ”8-bit” processor label historically denotes an 8-bit ALU and an 8-bit external data bus. This allows byte-wide transfers in a single bus cycle. Address buses are often wider (e.g., 16 bits) to select many memory locations, but data bus width defines the size of each atomic data transfer. Step-by-Step Solution: Recognize the 8-bit processor class: byte-level operations.Match bus to processor width: external data bus = 8 bits.Confirm by device documentation: 8085 data bus D0–D7 (8 lines).Therefore, the correct choice is 8 bits. Verification / Alternative check: Look at pinouts: the 8085 has D0 through D7 pins, clearly indicating an 8-bit data bus. Why Other Options Are Wrong: 7 and 9: nonstandard widths for classic 8-bit MCUs/MPUs.16: corresponds to 16-bit processors (e.g., 8086 external data bus is 16 bits), not an 8-bit device. Common Pitfalls: Confusing address bus width (often 16 bits in 8-bit systems) with data bus width (8 bits). These serve different roles. Final Answer: 8

Question 2

8085-style microprocessor basics: In the same 8-bit microprocessor system context, how many bits wide is the address bus typically used to select memory locations?

Accepted Answer

Introduction / Context: The address bus width sets the maximum number of uniquely addressable locations. Many classic 8-bit processors pair an 8-bit data bus with a wider address bus to access a larger memory space. This question targets the typical address width for such systems (e.g., Intel 8085). Given Data / Assumptions: 8-bit microprocessor class (e.g., 8085). We refer to the external address bus width. Linear addressing without bank switching. Concept / Approach: The Intel 8085 exposes a 16-bit address bus (A0–A15), allowing 2^16 = 65,536 distinct addresses. When each address maps to a byte, this equals 64 KB of addressable memory. Many contemporary 8-bit processors followed this convention for simplicity and sufficient space for code and data of the era. Step-by-Step Solution: Identify typical address bus width: 16 bits for 8085-class CPUs.Compute capacity: 2^16 = 65,536 locations.Relate to memory size: 65,536 bytes = 64 KB.Conclude the correct answer is 16 bits. Verification / Alternative check: Pinout references show A0–A15 lines on the 8085, confirming a 16-bit address path. Why Other Options Are Wrong: 7, 8, 9: far too small to provide the conventional 64 KB space of classic 8-bit MPUs. Common Pitfalls: Assuming data bus width equals address bus width. They are independent: one describes data quantity per transfer, the other defines addressable range. Final Answer: 16

Question 3

Computer architecture basics: A system built from a microprocessor unit (MPU), a memory unit, and input/output (I/O) interfaces together forms which type of digital system?

Accepted Answer

Introduction / Context: A complete computing system needs processing, storage, and I/O. Recognizing the minimal set of building blocks clarifies terminology used in embedded systems and classic computer architecture descriptions. Given Data / Assumptions: Microprocessor unit (central processing chip). Memory unit (ROM/RAM/flash). Input/Output interfaces (ports, peripherals, buses). Concept / Approach: A central processing unit alone is not sufficient. When you add memory and I/O around a microprocessor, you obtain a complete microcomputer. The term CPU refers to the processing core; ALU is only the arithmetic-logic component within the CPU; a compiler is a software tool, not hardware. Step-by-Step Solution: Start with MPU: executes instructions.Add memory: stores program and data.Add I/O: enables interaction with external devices and users.These three together constitute a microcomputer. Verification / Alternative check: Block diagrams in textbooks show the microprocessor at the center with address/data/control buses connected to memory and I/O, labeled ”microcomputer system”. Why Other Options Are Wrong: CPU: only the processing core, not a full system.Compiler: software, not hardware architecture.ALU: a sub-block inside the CPU. Common Pitfalls: Using CPU and microprocessor interchangeably with microcomputer; the latter implies a complete, usable system. Final Answer: microcomputer

Question 4

Digital I/O fundamentals: In general-purpose digital interfaces, a port can be configured for which directions of data flow?

Accepted Answer

Introduction / Context: Microcontrollers and microprocessor systems expose ports to interact with external circuits. Ports can be designed or configured to accept data, drive data, or do both depending on the application and hardware capabilities. Given Data / Assumptions: General-purpose I/O (GPIO) concept applies. Hardware may support direction control via configuration registers. Some peripherals use dedicated input-only or output-only pins. Concept / Approach: An I/O port is an interface abstraction. Depending on design, it may be input-only (e.g., status sensing), output-only (e.g., LED drive), or bidirectional (e.g., data bus lines, GPIO pins). Many devices allow run-time direction control for flexibility. Step-by-Step Solution: Identify port types: input, output, bidirectional.Match to use cases: inputs read sensors; outputs drive actuators; bidirectional lines share roles (often with tri-state control).Recognize configuration: direction registers/tri-state buffers enable dynamic role changes.Therefore, all three are possible roles for ports. Verification / Alternative check: Examine datasheets: GPIO pins commonly have direction bits; parallel ports support input/output modes; buses use bidirectional signals with enable control. Why Other Options Are Wrong: Restricting to only one direction ignores the flexibility of modern port designs. Common Pitfalls: Forgetting to handle contention on bidirectional lines; proper use of direction control and tri-state is essential to avoid bus conflicts. Final Answer: all the above

Question 5

Microprocessor internals: Which of the following is NOT a basic internal element of a microprocessor chip?

Accepted Answer

Introduction / Context: Microprocessors contain standard building blocks to execute instructions efficiently. Distinguishing core internal elements from separate device classes (like microcontrollers) prevents confusion when reading datasheets or block diagrams. Given Data / Assumptions: We consider a classic microprocessor (MPU), not a full microcontroller (MCU). Typical internal blocks include ALU, accumulator, registers, control unit. The ”temporary register” denotes general-purpose or intermediate storage. Concept / Approach: An ALU performs arithmetic/logic operations. The accumulator is a key register for intermediate results in many architectures. Temporary/general registers support operations and addressing. By contrast, a microcontroller is a complete system-on-chip (CPU + memory + peripherals), not a sub-block inside a microprocessor. Step-by-Step Solution: Identify components commonly inside a CPU: ALU, accumulator, registers → valid internal elements.Recognize that a ”microcontroller” is a higher-level device integrating a microprocessor core with memory/I/O.Therefore, ”microcontroller” is not an internal element of a microprocessor.Select: microcontroller. Verification / Alternative check: Block diagrams of 8085/8086 and similar processors show ALU, register file, accumulator, instruction decoder/control unit; they do not list ”microcontroller” as a block. Why Other Options Are Wrong: ALU, temporary register, accumulator are standard internal CPU components. Common Pitfalls: Conflating MPU and MCU. An MCU includes a CPU core but is not a component of a CPU. Final Answer: microcontroller

Question 6

Computer buses: Which of the following is NOT a standard bus type used in microprocessor systems?

Accepted Answer

Introduction / Context: Microprocessor systems communicate over well-defined buses. Knowing the canonical bus types clarifies system diagrams and helps troubleshoot hardware issues involving signal lines and timing. Given Data / Assumptions: Standard buses in basic systems include data, address, and control buses. Specialized peripherals may include timer modules but not a separate ”timer bus”. We consider foundational bus taxonomy, not proprietary interconnect names. Concept / Approach: The data bus transfers data values; the address bus selects memory or I/O locations; the control bus carries control signals (e.g., read/write strobes, clock, interrupts). ”Timer bus” is not a standard category; timers are peripherals connected via the existing buses. Step-by-Step Solution: List canonical buses: data, address, control.Check ”timer bus”: not part of the canonical set; timers are mapped on the existing buses.Therefore, ”timer bus” is not a standard bus type.Select: timer bus. Verification / Alternative check: Reference any introductory computer organization text: the three-bus model (address, data, control) is foundational and widely taught. Why Other Options Are Wrong: Data, address, control buses are essential and ubiquitous in processor architectures. Common Pitfalls: Mistaking a peripheral function (timers) for a separate interconnect category. Final Answer: timer bus

Question 7

8085 microprocessor concepts: In the Intel 8085, events that temporarily suspend normal instruction execution so the processor can service an external or internal request are known as what?

Accepted Answer

Introduction / Context: Real-time systems require the CPU to respond to asynchronous events like I/O readiness, timers, or faults. Microprocessors provide a mechanism to suspend the current program and execute a service routine. In 8085 terminology, these are ”interrupts”. Given Data / Assumptions: Target device: Intel 8085 microprocessor. Events are exceptional with respect to sequential instruction flow. Hardware and software interrupt vectors are part of the architecture. Concept / Approach: An interrupt signals the CPU to save its context and branch to a predefined service routine address. After servicing, the CPU returns to the interrupted task. This differs from a jump instruction, which is a deliberate program flow change initiated by software within the current execution stream. Step-by-Step Solution: Identify the nature of the ”exception”: asynchronous/exceptional events.Map to processor feature: interrupts handle such events (e.g., RST vectors in 8085).Differentiate from jumps: jumps are normal instructions; they do not suspend in response to external requests.Therefore, the correct term is ”interrupts”. Verification / Alternative check: 8085 supports several interrupt lines (e.g., TRAP, RST7.5, RST6.5, RST5.5, INTR) and a software interrupt mechanism (RST n), confirming the architectural support for interrupt-driven control. Why Other Options Are Wrong: Jump instructions: normal control-flow instructions; not asynchronous exceptions.Decoding: refers to instruction decode stage; not an exception mechanism.Jump instructions or interrupts: too broad; the question specifically asks for exceptions to normal operation. Common Pitfalls: Confusing subroutine calls or jumps with interrupts. Interrupts can arrive at any time (subject to masking/priority) and are serviced by hardware mechanisms that save/restore context. Final Answer: interrupts

Question 8

In computer architecture and assembly language, what is the key difference between mnemonic codes and machine codes? Provide the most accurate description comparing their human readability and representation.

Accepted Answer

Introduction / Context: Assembly programming bridges human intent and hardware execution. The same instruction can be expressed in two forms: a human-readable shorthand known as a mnemonic, and a hardware-executable machine code composed of binary patterns. Understanding this distinction is foundational for anyone working with assemblers, disassemblers, or embedded firmware. Given Data / Assumptions: A processor executes binary opcodes and operands. Assembly language exposes those operations with short words such as MOV, ADD, JMP. An assembler converts mnemonics to numeric opcodes; a disassembler does the reverse best-effort. Concept / Approach: Machine code is the literal binary (or hex) encoding that a CPU fetches and executes. Mnemonics are symbolic names for those opcodes that humans can read, write, and reason about. The assembler maps each mnemonic plus addressing mode and operands to a specific opcode pattern and operand fields. The mapping is architecture specific, which is why mnemonics differ across CPU families even for similar operations. Step-by-Step Solution: Identify what hardware consumes: binary instruction words (machine codes).Identify what programmers commonly write: symbolic instructions (mnemonics) like MOV R1, R2.State the translation: assembler converts mnemonics to machine code and resolves labels to addresses.Conclude: machine codes are binary; mnemonics are shorthand English tokens that represent them. Verification / Alternative check: Examine an object file or a hex dump. Each instruction appears as bytes (for example, 0xB8 0x34 0x12). A disassembler shows the corresponding mnemonic (for example, MOV AX,1234h). This demonstrates the one-to-one mapping between human-readable mnemonics and binary encodings for a given architecture. Why Other Options Are Wrong: There is no difference: false; representation and audience differ. Machine codes as shorthand English or high level: incorrect; machine code is binary. Compiler to C: unrelated to assembly mnemonics and machine encodings. Common Pitfalls: Confusing assembly with high-level languages or assuming the same mnemonics across architectures. Mnemonic sets vary; the binary is always the CPU's ground truth. Final Answer: Machine codes are in binary, mnemonic codes are in shorthand English.

Question 9

In microprocessor I/O design, what is the technique called in which each input/output device is assigned a unique address within the normal memory address space so that the CPU can access devices using standard memory read/write instructions?

Accepted Answer

Introduction / Context: Processors communicate with peripherals either through a separate I/O address space or by treating peripheral registers as if they were memory locations. The latter approach is widely used in microcontrollers and many CPU architectures because it simplifies instruction sets and programming models. Given Data / Assumptions: Each device register is reachable with a unique address. Standard load/store instructions are used to access devices. No special I/O opcodes are required. Concept / Approach: Memory-mapped I/O integrates device registers into the processor's memory space. Reading or writing a specific address triggers peripheral hardware rather than returning ordinary RAM contents. This enables uniform access semantics and allows compilers to treat device registers as volatile memory locations. Step-by-Step Solution: Define the approach: devices appear at fixed addresses within the memory map.CPU uses the same bus cycles and control signals used for RAM to reach device registers.Software uses ordinary load/store instructions to configure and read devices.Therefore, the technique is called memory-mapped I/O. Verification / Alternative check: Inspect any common microcontroller datasheet: peripheral registers are listed with absolute addresses, and code uses standard read/write with volatile qualifiers to access them. Why Other Options Are Wrong: Wired I/O and dedicated I/O are vague terms and not the standard name. I/O mapping is generic wording; the precise term is memory-mapped I/O. Port-isolated I/O refers to a separate I/O space, which is the alternate method, not this one. Common Pitfalls: Assuming all CPUs support only one method. Some architectures provide both isolated I/O and memory-mapped I/O; software must follow the platform convention. Final Answer: memory-mapped I/O

Question 10

For the Intel 8085 microprocessor hardware organization, how many primary system buses are provided and named?

Accepted Answer

Introduction / Context: Classic microprocessors, including the Intel 8085, are described in terms of their system buses. Each bus plays a distinct role in moving addresses, data, and control information between the CPU and memory or peripherals. Given Data / Assumptions: 8085 uses conventional bus partitioning. We focus on the primary buses, not internal micro-architectural paths. Names are address bus, data bus, and control bus. Concept / Approach: Microprocessors typically expose three external buses: an address bus (unidirectional from CPU), a data bus (bidirectional), and a control bus (signals such as RD, WR, ALE, IO/M). Knowing the count and directionality is basic to understanding memory maps and peripheral interfacing. Step-by-Step Solution: List the buses: address, data, control.Address bus carries location information to select memory or I/O registers.Data bus carries operand and result bytes both to and from the CPU.Control bus coordinates timing and read/write strobes. Verification / Alternative check: Any 8085 block diagram shows these three grouped signal sets explicitly, confirming the total as three. Why Other Options Are Wrong: 2 or 4 or more than 3: do not match the standard external organization for the 8085. 5 or 8: exceed the canonical grouping, confusing individual lines with bus categories. Common Pitfalls: Counting internal paths or individual control lines as separate buses. The conventional answer groups signals into the three system buses. Final Answer: 3

Question 11

When describing assembly instruction words, what does the term mnemonic most precisely represent in the instruction format?

Accepted Answer

Introduction / Context: Assembly language expresses machine instructions using symbolic elements. Disentangling the role of each element (mnemonic, operands, labels, addressing modes) is essential to read or write assembly code with confidence. Given Data / Assumptions: An instruction typically comprises a mnemonic and zero or more operands. Operands may be registers, immediate values, or memory references. Labels name addresses and are not the mnemonic itself. Concept / Approach: The mnemonic is the terse keyword naming the operation: for example, MOV, ADD, SUB, JMP. Operands specify sources, destinations, or addresses. The assembler maps the mnemonic plus operands to a specific opcode pattern appropriate for the architecture. Step-by-Step Solution: Identify the instruction form: MNEMONIC OPERAND(S).Map examples: MOV R0, #5 loads an immediate; ADD R1, R2 adds two registers.Note that the mnemonic names the operation (move, add, jump).Therefore, the definition is a short abbreviation for the operation to be performed. Verification / Alternative check: Consult any assembler reference; each entry is keyed by mnemonic name and describes the operation semantics and encoding forms for its operands. Why Other Options Are Wrong: Operand address or data word: these are operand fields, not the mnemonic. Shorthand for machine language: misleading; mnemonics are symbolic, not the binary itself. Label: labels are identifiers for addresses and are distinct from mnemonics. Common Pitfalls: Confusing labels or pseudo-ops (directives) with real instruction mnemonics. Pseudo-ops control the assembler, not the CPU. Final Answer: a short abbreviation for the operation to be performed

Question 12

Within a typical microprocessor system, which system bus is inherently bidirectional because it must both carry data to the CPU and carry results or read data away from the CPU?

Accepted Answer

Introduction / Context: Buses are shared signal pathways that connect the CPU to memory and peripherals. Directionality distinguishes how information flows. Recognizing which bus must support two-way transfer helps with interfacing and timing analysis. Given Data / Assumptions: Three primary buses: address, data, and control. The CPU both reads and writes data. Address selection is driven by the CPU outward. Concept / Approach: The address bus is unidirectional from CPU to memory/I/O because only the CPU selects the target location. The data bus must be bidirectional so that data can flow into the CPU during reads and out from the CPU during writes. The control bus carries timing and control lines and is not a data-carrying bidirectional bus in the same sense. Step-by-Step Solution: Identify read cycle: external device drives data toward the CPU.Identify write cycle: CPU drives data toward the device.Therefore, the data bus must support both directions (bidirectional).Confirm that the address bus only carries addresses from the CPU to devices. Verification / Alternative check: Timing diagrams show that on reads, data bus lines are inputs to the CPU; on writes, they become outputs. Tri-state drivers and bus turn-around timing maintain safe direction changes. Why Other Options Are Wrong: Control bus: carries strobes and status signals; not bidirectional data lines. Address bus: unidirectional from CPU to target. Multiplexed bus: a technique to share lines over time; it does not define directionality by itself. Status bus: not the primary bidirectional data path. Common Pitfalls: Assuming multiplexing implies bidirectionality. Multiplexed address/data buses still separate roles by phase and use direction control logic. Final Answer: data bus

Question 13

In embedded and microprocessor-based products, what term best describes the software that is stored in nonvolatile memory and is intended to control the hardware at a low level during normal operation and startup?

Accepted Answer

Introduction / Context: From appliances to automobiles, microcontrollers execute software that initializes hardware, runs control loops, and manages I/O. This class of software is typically embedded into nonvolatile memory so it persists across power cycles. Given Data / Assumptions: Software resides in ROM, flash, or OTP memory. It boots hardware, configures peripherals, and implements device functions. It is specific to the product and hardware platform. Concept / Approach: The industry term for this is firmware. Unlike general-purpose application software, firmware is tightly coupled to hardware and often runs without a traditional operating system. It can be updated in the field, but it remains part of the device image that defines behavior at power-on. Step-by-Step Solution: Recognize storage: nonvolatile memory within the device.Recognize role: hardware bring-up, control, and continuous operation.Map to terminology: such software is called firmware.Exclude distractors that are not categories of embedded control software. Verification / Alternative check: Device manuals refer to firmware versions. Update utilities flash new firmware images to correct bugs and add features while preserving device-specific functionality. Why Other Options Are Wrong: Assembly language programs: a programming notation, not a deployment category. BASIC interpreter instructions and flowchart instructions: methods or notations, not the persistent device software category. Middleware: sits between OS and applications; many embedded devices have no such layer. Common Pitfalls: Confusing the language used (C, assembly) with the deployment category. Firmware describes purpose and placement, not syntax. Final Answer: firmware

Question 14

Coprocessor concept (definition check): A coprocessor is a specialized microprocessor with a focused instruction set optimized to perform arithmetic or other specific operations very quickly. Is this statement accurate for typical math/FPU coprocess…

Accepted Answer

Introduction / Context: Coprocessors augment a general-purpose CPU by handling particular classes of operations more efficiently. Classic examples include floating-point units (FPUs), graphics coprocessors, and cryptographic accelerators. They typically implement a narrower, domain-specific instruction set and provide hardware datapaths optimized for those operations, thereby speeding up tasks that would be slower in the general CPU. Given Data / Assumptions: “Coprocessor” refers to a processor working alongside a host CPU. Typical targets: floating-point arithmetic, vector/graphics, encryption/decryption. Instruction sets are specialized, not full general-purpose ISA replacements. Concept / Approach: An FPU coprocessor executes arithmetic-intensive instructions (add, multiply, divide, transcendental functions) using dedicated pipelines and wide datapaths. Because the instruction repertoire and microarchitecture are focused, performance per watt and per cycle for those tasks is much higher than emulation in software on the main CPU. This design epitomizes a “limited instruction set optimized for speed” in its domain, making the statement accurate. Step-by-Step Solution: Identify scope: coprocessor assists the CPU for specific operations.Relate to instruction set: targeted, not general-purpose.Tie to performance: dedicated hardware achieves much faster arithmetic than software routines.Conclude the statement accurately describes typical coprocessors. Verification / Alternative check: Historically, x87 FPUs (e.g., 8087) accelerated floating-point by orders of magnitude compared to integer-only CPUs. Modern SoCs integrate similar accelerators (NEON, AVX units, GPU shaders, AES engines) that embody the same principle. Why Other Options Are Wrong: Limiting to DSPs or GPUs ignores FPUs and crypto engines. Microcoding is an implementation detail; specialization does not require microcode. “Incorrect” contradicts widespread design practice. Common Pitfalls: Confusing coprocessors with general multicore CPUs; assuming “limited” implies weak—specialization yields higher performance in the target domain. Final Answer: Correct

Question 15

Machine vs assembly language: Is the language directly understood and executed by a microprocessor called “assembly language,” or does that term refer to a different, human-readable representation?

Accepted Answer

Introduction / Context: Programmers often encounter multiple layers of representation: high-level languages, assembly, and machine code. Knowing which layer the CPU actually executes is foundational to understanding toolchains, compilers, and performance tuning. The question tests whether “assembly language” is what the processor directly understands. Given Data / Assumptions: The CPU ultimately fetches and executes binary opcodes. Assembly language is a mnemonic, human-readable form of those opcodes. An assembler translates assembly into machine language (binary). Concept / Approach: Processors execute machine language—binary instruction codes defined by the ISA. Assembly is a symbolic representation (e.g., MOV R1, R2) that must be assembled into opcodes (e.g., 0xXYZZ). Therefore, saying the microprocessor “understands assembly” is not precise; it understands the binary form. Assemblers, linkers, and loaders bridge the gap between human-readable source and executable machine code. Step-by-Step Solution: Identify CPU input: binary opcodes + operands (machine language).Define assembly: mnemonics/symbols that map 1:1 (or nearly so) to opcodes.Conclude: the statement is incorrect; the CPU understands machine language, not assembly. Verification / Alternative check: Object files contain machine code and metadata. Disassemblers reverse this mapping to assembly mnemonics—confirming assembly is a representation, not the executed form. Why Other Options Are Wrong: Architecture type (CISC/RISC), linking stage, or assembler brand does not change the fact that the CPU executes binary machine code. Common Pitfalls: Equating “assembly-level programming” with direct hardware execution; forgetting the assembler translation step and object code format. Final Answer: Incorrect

Question 16

Portability of machine language: Is machine language (binary opcodes) independent of the microprocessor type, or is it architecture-specific and therefore not portable across different CPUs?

Accepted Answer

Introduction / Context: Machine language is the lowest-level programming representation: the exact bit patterns that a CPU decodes into actions. Whether those bit patterns are portable across different processors is a critical concept for cross-platform development and binary compatibility. Given Data / Assumptions: Different microprocessor families define different Instruction Set Architectures (ISAs). Opcodes, encodings, and calling conventions vary significantly by ISA. Endianness and operating systems are additional—but separate—considerations. Concept / Approach: Machine language is inherently architecture-specific. A binary compiled for one ISA (e.g., ARM, x86, RISC-V) is not understood by a different ISA because the opcode encodings and instruction semantics differ. Portability is achieved by recompiling source code for the target ISA or by using emulation/translation layers, not by reusing the same machine code bits. Step-by-Step Solution: Define “machine language”: ISA-specific opcode encodings.Compare ISAs: differing instruction formats and operation codes.Conclude: the statement “machine language is independent of microprocessor type” is incorrect. Verification / Alternative check: Attempting to execute x86 binaries on ARM without translation fails; cross-compilation produces new machine code tailored to the target ISA. This confirms architecture dependence. Why Other Options Are Wrong: RISC vs CISC is irrelevant to the portability fact. Recompilation changes the machine code, not its independence. Endianness alone does not harmonize different opcodes. Common Pitfalls: Confusing portability of high-level source with portability of binaries; assuming shared endianness or OS ABI implies instruction compatibility. Final Answer: Incorrect

Question 17

Computer architecture fundamentals (assembly language): a mnemonic is an English-like assembly instruction that an assembler translates into the actual processor's machine code for execution. Confirm or refute this description.

Accepted Answer

Introduction / Context: Programmers rarely write long streams of raw opcodes like 3E or C3. Instead, they use human-readable operation names called mnemonics, such as MOV, ADD, or JMP. This question checks whether you understand the role of an assembler: converting those mnemonics and operands into the exact sequence of machine code bytes a CPU can execute. Given Data / Assumptions: We are discussing assembly language development for a conventional microprocessor. Mnemonic examples: MOV A, B; ADD R1, #05; JMP 2000H. Assembler output is object code (binary) mapped to the target instruction set. Linking/relocation may follow assembly but is not required for the definition. Concept / Approach: Assembly language is a symbolic representation of machine language. Each mnemonic corresponds to one instruction opcode (sometimes with addressing-mode dependent encodings), and operands become fields or immediate bytes. The assembler resolves symbols (labels), computes addresses, and emits machine code. Therefore, mnemonics are indeed English-like directives that the assembler translates into the processor’s native encoding. Step-by-Step Solution: 1) Identify a mnemonic such as MOV A, #12H. 2) The assembler looks up the opcode for MOV-immediate-to-A and encodes the immediate operand 12H. 3) It outputs the correct byte sequence (e.g., opcode byte followed by 12H), forming machine code. 4) The CPU later fetches and executes those bytes; it never sees the mnemonic text. Verification / Alternative check: Examine a listing file: it shows each source line alongside the emitted hex bytes, demonstrating the direct translation from mnemonic to machine code. Why Other Options Are Wrong: Does not apply: ignores the fundamental purpose of an assembler. “Only on RISC” or “only with a linker” adds constraints that are not part of the definition. Common Pitfalls: Confusing assembler (source to object) with compiler (high-level to object). Believing the CPU “understands” mnemonics—only machine code is executed. Final Answer: Applies

Question 18

Instruction timing terminology: a machine cycle vs. an instruction cycle—does a single “machine cycle” mean the time to fetch and execute a complete instruction?

Accepted Answer

Introduction / Context: Precise timing vocabulary matters in microprocessor design. Two terms are often mixed up: machine cycle (sometimes called bus cycle or memory cycle) and instruction cycle (fetch + execute sequence). This question tests whether you can distinguish them correctly. Given Data / Assumptions: An instruction may require several bus operations: opcode fetch, operand read/write, stack access, etc. Each bus operation consumes one or more clock periods and is termed a machine cycle. The total time to complete an instruction is the instruction cycle, which can span multiple machine cycles. Concept / Approach: Machine cycle: the smallest external bus transaction window during which the CPU places an address, asserts control signals (RD, WR, etc.), and transfers a data byte/word. Instruction cycle: the aggregate of all machine cycles required to fetch, decode, and execute one instruction. Therefore, it is incorrect to define a machine cycle as “the time to fetch and execute a complete instruction.” Step-by-Step Solution: 1) Identify an instruction (e.g., a memory-reference instruction). 2) Break it into required machine cycles: opcode fetch, memory read, possibly memory write. 3) Sum these machine cycles to get the instruction cycle time. 4) Conclude: a machine cycle is a sub-unit of an instruction cycle, not the whole. Verification / Alternative check: Timing diagrams and datasheets list distinct opcode-fetch and memory-access cycles for many instructions; the total count varies by instruction, confirming the distinction. Why Other Options Are Wrong: Applies: confuses the hierarchy of timing terms. Adding “single-byte opcode” or “microcoded CPU” does not change the core definitions. Common Pitfalls: Equating the simplest instruction’s total time to a universal “machine cycle” definition; ignoring that multi-byte or multi-step instructions need several cycles. Final Answer: Does not apply

Question 19

Microprocessor buses: is an address bus typically unidirectional (from CPU to memory/IO) because only the processor drives physical addresses?

Accepted Answer

Introduction / Context: A basic microprocessor system uses three bus types: address, data, and control. Understanding their directions clarifies how components communicate. This question checks whether the address bus is rightly termed “unidirectional.” Given Data / Assumptions: Conventional CPU-connected memory or peripherals (no exotic bus bridges). Address lines A[n:0] are driven by the CPU to specify a location. Data bus allows reading or writing actual data values. Control bus conveys signals such as RD, WR, IO/M, CS. Concept / Approach: Only the CPU (or a current bus master like a DMA controller when bus-mastering) asserts the physical address that selects a memory or IO location. Thus, from the CPU’s perspective, address lines are driven outward; memory devices do not drive addresses back to the CPU. Hence, the address bus is termed unidirectional. Even when DMA masters take control, they become the driver; the bus still carries addresses in one direction from the current master to the slaves. Step-by-Step Solution: 1) CPU places an address on A[n:0]. 2) Control signals qualify the type of access (read or write). 3) The selected device responds on the data bus; address lines remain outputs from the master. 4) Therefore, the address bus is unidirectional with respect to the driving master. Verification / Alternative check: CPU pin descriptions show address pins as outputs, while data pins are typically bidirectional. Why Other Options Are Wrong: Does not apply: denies standard bus directionality. “Only if DMA is disabled” or “only Harvard” add conditions that do not alter the basic definition. Common Pitfalls: Confusing bus arbitration (who drives) with signal direction on a given transaction; assuming address echoing can occur from memory (it does not). Final Answer: Applies

Question 20

Language translation pipeline: is a compiler a translator that converts high-level language source code into a set of executable machine instructions (object code/binaries)?

Accepted Answer

Introduction / Context: Software moves from human-friendly forms to CPU-executable forms through translation tools. This question distinguishes the compiler’s role from assemblers and interpreters. Given Data / Assumptions: High-level languages include C, C++, Java (ahead-of-time), Rust, etc. Compiler output may be object files needing linking into executables. Target is machine code for a specified architecture (e.g., x86, ARM). JIT compilers are special cases layered in runtime environments. Concept / Approach: A compiler parses high-level syntax, performs semantic analysis and optimization, and emits machine code or an intermediate object file that is later linked. The result is a binary executable or library that the CPU can run. This is distinct from an assembler (assembly → machine) and an interpreter (executes source or bytecode step-by-step without producing a final native binary ahead of time). Step-by-Step Solution: 1) Source code is tokenized and parsed into an abstract syntax tree. 2) The compiler checks types, performs analysis/optimizations. 3) It generates machine code or intermediate representation, then object files. 4) A linker resolves symbols and produces the final executable binary. Verification / Alternative check: Build tools (e.g., gcc/clang) produce .o/.obj and then link to an .exe/.elf, demonstrating translation to machine code. Why Other Options Are Wrong: Does not apply: contradicts the role of a compiler. JIT is optional and not required. Assembly is translated by an assembler, not a high-level language compiler. Common Pitfalls: Confusing bytecode VMs with native compilation; equating “compiler” with “interpreter.” Final Answer: Applies

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