Question 1

8085 addressing width and storage: an 8085 address is 16 bits—does it require two consecutive 8-bit memory locations to store such an address, or “two locations of 16 bits each” as sometimes misstated?

Accepted Answer

Introduction / Context: The Intel 8085 has a 16-bit address space (0000H–FFFFH). Memory is byte addressed, and every memory location stores exactly 8 bits. This question clarifies how a 16-bit address value itself is stored in memory. Given Data / Assumptions: 8085 address space width: 16 bits. Memory is byte-addressable: one address → one byte (8 bits). Endianness conventions may apply (low byte, high byte order) depending on instruction. Concept / Approach: A 16-bit quantity occupies two bytes. Therefore, to store an address value (e.g., the contents of the program counter or a pointer), two consecutive memory locations are used—each holding 8 bits. Any wording that says “two memory locations (16 bits each)” is incorrect because standard memory locations are 8 bits on 8085-class systems. Step-by-Step Solution: 1) Recognize: one memory location = 8 bits (1 byte). 2) A 16-bit address therefore needs 2 bytes. 3) Store low-order byte in the lower address and high-order byte in the higher address (or per ISA convention). 4) Reading back two bytes reconstructs the 16-bit address. Verification / Alternative check: Instruction encodings for CALL/JMP and stack PUSH/POP on 8085 show low-byte/high-byte storage across two consecutive bytes. Why Other Options Are Wrong: “Two 16-bit locations” do not exist on byte-addressable 8085 memory. “Three bytes due to parity” is irrelevant. “Only the stack” is false; any memory can store addresses. Common Pitfalls: Confusing word-sized storage with location size; overlooking endianness when reading/writing multi-byte quantities. Final Answer: Applies (two 8-bit locations store a 16-bit address)

Question 2

Bus pin minimization on 8085: to reduce IC pin count, does the 8085 multiplex address and data on the same physical lines (AD0–AD7) using an address latch?

Accepted Answer

Introduction / Context: Chip packaging limits push designers to share pins across functions. The Intel 8085 is a classic example: it multiplexes low-order address bits and data on the same eight pins to keep the package small and cost-effective. Given Data / Assumptions: 8085 uses pins AD0–AD7 for address/data multiplexing. ALE (Address Latch Enable) strobes an external latch to capture the low address byte. High address bits (A8–A15) are on dedicated pins. Concept / Approach: During the beginning of a machine cycle, AD0–AD7 carry the low-order address bits (A0–A7). ALE goes high to latch these into an external address latch (e.g., 74HC373). After latching, the same AD pins switch function to carry data (D0–D7) for the remainder of the cycle. This time-division sharing saves eight pins while preserving full functionality. Step-by-Step Solution: 1) CPU outputs low address on AD lines; ALE pulses. 2) External latch stores A0–A7 so memory sees a stable 16-bit address (A8–A15 direct + latched A0–A7). 3) AD lines then switch to data mode for read/write. 4) Control lines (RD, WR, IO/M) qualify the transfer. Verification / Alternative check: Timing diagrams in 8085 references show ALE transitions and AD line role switching within a machine cycle. Why Other Options Are Wrong: Does not apply: contradicts published bus operation. Tying it to DMA or 16-bit CPUs is incorrect: this is a feature of the 8-bit 8085. Common Pitfalls: Forgetting to add the external latch in hardware designs; mis-timing ALE in simulations. Final Answer: Applies

Question 3

Control vs. data buses: do the control bus and memory devices “share a bidirectional bus,” or are control signals generally unidirectional lines coordinating reads/writes alongside a separate bidirectional data bus?

Accepted Answer

Introduction / Context: In a classic microprocessor architecture, three buses cooperate: address (usually unidirectional), data (bidirectional), and control (directional lines for timing/qualification). This question corrects a common misconception that control and memory “share a bidirectional bus.” Given Data / Assumptions: Control lines include RD, WR, IO/M, ALE, CS, READY, etc. Data bus carries payload bytes in both directions. Address bus selects the target location or device. Concept / Approach: The control bus is not a unified bidirectional data path. It consists of distinct signals, each with a defined direction: for example, RD and WR are CPU outputs that indicate read or write. Chip Select (CS) is usually driven from decoding logic to the memory/peripheral. Data actually flows on the data bus, which is bidirectional. Therefore, the statement that “control bus and memories share a bidirectional bus” conflates roles: control signals coordinate the transfer; they are not the medium that carries data both ways. Step-by-Step Solution: 1) CPU places an address on A[n:0]. 2) CPU asserts control: RD=1 to read or WR=1 to write (direction is CPU → device). 3) Data then moves on the data bus: device → CPU for reads; CPU → device for writes. 4) Control lines return inactive; bus cycle completes. Verification / Alternative check: Pinout tables show data lines as bidirectional and control lines as outputs/inputs with defined roles, not a shared bidirectional channel. Why Other Options Are Wrong: “Applies” misrepresents bus functions. DMA and tri-state details do not change the conceptual separation of control versus data pathways. Common Pitfalls: Thinking “bus” always implies a single shared set of lines; overlooking that control is a set of coordination signals, not a data path. Final Answer: Does not apply (control lines direct transactions; data bus is separate and bidirectional)

Question 4

8085 register roles: which register tracks the memory address of the next opcode to be fetched and executed during program flow?

Accepted Answer

Introduction / Context: Every CPU has dedicated registers for specific tasks. One of the most important is the register that holds the address of the next instruction to fetch. In 8085 terminology, this register is the Program Counter (PC). Given Data / Assumptions: 8085 has a 16-bit Program Counter and 16-bit Stack Pointer. PC automatically increments after fetching an opcode or immediate data bytes. Control-flow instructions (JMP, CALL, RET, conditional branches) modify PC. Concept / Approach: The fetch-decode-execute cycle begins with the PC pointing to the next opcode. After fetch, PC advances by one or more bytes depending on instruction length. When a branch or call occurs, the PC is loaded with a new target address (sometimes after pushing the return address to the stack). Thus, the PC is the register that “tracks the memory address of the next opcode.” Step-by-Step Solution: 1) PC → address bus (opcode fetch). 2) CPU reads the opcode; PC increments. 3) If the instruction has immediate/address bytes, PC advances accordingly. 4) Control-flow instructions load PC with a new value (branch target). Verification / Alternative check: Instruction set documentation labels the PC as the source of the next fetch address; stack operations involve SP, not PC. Why Other Options Are Wrong: Stack pointer manages call/return stack, not instruction sequencing. “Instruction pointer” is x86 naming; 8085 uses “Program Counter.” Accumulator stores arithmetic/logic results, not addresses. Common Pitfalls: Mixing architecture-specific names; assuming accumulator controls instruction flow. Final Answer: program counter

Question 5

CPU result register identification: which register records the current arithmetic/logic operation result in classic 8-bit microprocessors like the 8085?

Accepted Answer

Introduction / Context: In accumulator-based architectures, most arithmetic and logic operations use a special register called the accumulator (A or ACC). Understanding its role is foundational to assembly programming and CPU design. Given Data / Assumptions: 8085 uses an 8-bit accumulator denoted as A. Typical ALU operations read/write the accumulator. Status flags reflect properties of the last ALU result (Zero, Sign, Carry, etc.). Concept / Approach: The accumulator is the primary destination for ALU outputs. ADD, SUB, ANA, ORA, XRA, INR/DCR, and similar instructions place the result in A, updating flags accordingly. While some instructions store results to memory or other registers, the default pattern is that A receives the current result, making “accumulator” the correct answer. Step-by-Step Solution: 1) Execute an ALU instruction (e.g., ADD B). 2) The ALU computes A + B; the result is written back to A. 3) Flags are updated to represent the new result’s properties. 4) Subsequent instructions can test flags or move A’s value elsewhere. Verification / Alternative check: 8085 instruction summaries consistently show A as the implicit destination for many arithmetic/logic operations. Why Other Options Are Wrong: Program counter holds next instruction address. Stack pointer addresses top-of-stack. “Instruction pointer” is not an 8085 term. Common Pitfalls: Believing any general register always receives results; on 8085 the accumulator is central to ALU operations. Final Answer: accumulator

Question 6

Assembler output target: because CPUs cannot execute mnemonics directly, into what form must mnemonics be translated for the processor to run them?

Accepted Answer

Introduction / Context: Processors execute binary instructions—streams of bits that specify operations and operands according to the instruction set. Humans write assembly mnemonics for clarity, but those must be turned into executable bytes. This question asks for the correct execution form. Given Data / Assumptions: Assembly mnemonics are textual representations, not directly executable. Assembler translates mnemonics and operands into binary opcodes and data. Hexadecimal is a convenient human-readable representation of binary. Concept / Approach: The CPU fetches opcodes and operands from memory as binary values. Assembler tools map each mnemonic to the correct opcode and encode addressing modes and immediates. The resulting machine code may be displayed in hex (e.g., 3E 12 C3 00 20), but is stored and executed as binary. The essential point: the processor needs machine code—not high-level statements or mnemonics. Step-by-Step Solution: 1) Write source line: MVI A, 12H. 2) Assembler encodes opcode for MVI A and immediate 12H. 3) Output is machine code bytes, typically shown in hex. 4) Loader places bytes in memory; CPU fetches and executes them. Verification / Alternative check: Assembly listing files show each mnemonic with its corresponding hex bytes, confirming machine code as the execution form. Why Other Options Are Wrong: High-level language is a source form, not executable by the CPU. “Assembly language” is also source. “Machine code and assembly” together is incorrect; only machine code is executed. Common Pitfalls: Assuming hex text is different from machine code; hex is just a notation for the same binary bytes. Final Answer: hexadecimal machine code

Question 7

Computer architecture — instruction format basics: In machine language, the first field of an instruction that specifies the operation to be carried out (for example, add, load, jump) is called the __________.

Accepted Answer

Introduction / Context: Every processor executes binary instructions that are broken into fields. The field that tells the CPU what action to perform is critical because it determines which hardware pathways (datapath and control) activate. This question checks if you know the name of that instruction field in true machine language terminology. Given Data / Assumptions: The discussion refers to binary machine language, not assembly syntax. An instruction typically contains an operation field and one or more operand/addressing fields. Examples of operations include arithmetic, logic, data movement, and control flow. Concept / Approach: The operation code (abbreviated as opcode) is the part of the instruction that selects which operation the CPU performs. Control logic decodes the opcode into control signals. The remaining bits (operands, immediate data, or addressing mode specifiers) provide the data or references needed to complete the operation. Step-by-Step Solution: Identify the field naming conventions used in computer architecture.Map “first part that specifies the operation” to the standard term “opcode.”Confirm that mnemonics are human-readable assembly equivalents, not machine fields.Conclude that the correct term is opcode. Verification / Alternative check: Open any ISA reference (e.g., 8085, x86, ARM). The term “opcode” consistently labels the bits that select an instruction operation. Assemblers translate human mnemonics like MOV or ADD into opcodes. Why Other Options Are Wrong: mnemonic: Assembly-language shorthand for humans; not a machine field. interrupt: An external or internal event that diverts execution; not an instruction field. instruction cycle: A timing concept for fetch/execute; not a field inside an instruction. operation counter: Not a standard term in ISA documentation. Common Pitfalls: Confusing assembly mnemonics (text) with opcodes (binary). Assuming “first part” always means a fixed-length field—some ISAs use variable-length opcodes but the role is unchanged. Final Answer: opcode

Question 8

Toolchain basics — translating assembly to machine code: The __________ program converts human-readable mnemonic assembly into executable machine language for a specific processor.

Accepted Answer

Introduction / Context: Software toolchains transform source code into binaries. In low-level development, engineers write assembly using mnemonics that are easier to read than raw bits. A specialized program then converts this symbolic code into machine language instructions the CPU can directly execute. Given Data / Assumptions: Input: assembly source using mnemonics (e.g., MOV, ADD) and labels. Output: object or binary code composed of opcodes and data bytes for a target ISA. Target-dependent encoding: different CPUs have different opcode formats. Concept / Approach: An assembler reads assembly source, resolves symbols and labels, selects instruction encodings, and emits machine code. It may produce relocatable object files for later linking or absolute binaries for direct loading. This is distinct from compilers (which translate high-level languages to assembly or machine code) and linkers (which combine objects and resolve external references). Step-by-Step Solution: Identify the nature of the input (mnemonic assembly) and the desired output (machine code).Match the tool whose function is to assemble text into binary.That tool is called an “assembler.”Confirm by contrasting with compiler and linker roles. Verification / Alternative check: Classic tools like MASM, NASM, and GAS are described as assemblers, each producing machine code for their respective targets, often via an object file stage before linking. Why Other Options Are Wrong: debug: A debugger inspects and controls execution; it does not translate mnemonics to opcodes. C++ / fortran: High-level languages; their compilers may ultimately invoke an assembler but are not themselves the assembler. linker: Combines object files and resolves external symbols; does not perform mnemonic-to-opcode translation. Common Pitfalls: Conflating compiler and assembler roles, or assuming a debugger can generate final binaries from mnemonics without assembly. Final Answer: assembler

Question 9

8085 microprocessor — functional blocks: Within the 8085 CPU, the sub-block responsible for arithmetic and logical operations (add, subtract, AND, OR, compare) is called the __________.

Accepted Answer

Introduction / Context: Microprocessors are built from several cooperating blocks. Understanding which block does what helps when studying instruction execution and troubleshooting at the register/flag level. In the Intel 8085 (and most CPUs), arithmetic and boolean operations are concentrated in a single module. Given Data / Assumptions: Target device: Intel 8085 microprocessor as a representative 8-bit CPU. Operations of interest include arithmetic (add, subtract, increment) and logic (AND, OR, XOR, compare, rotate). Flags (e.g., zero, carry) reflect ALU results. Concept / Approach: The Arithmetic Logic Unit (ALU) executes integer arithmetic and bitwise operations and sets condition flags. The Control Unit sequences fetch/decode/execute; registers hold operands and results; buses move data and addresses. Together they form the CPU, but the ALU specifically performs the calculations asked in the prompt. Step-by-Step Solution: Identify the block that performs add/subtract/AND/OR.Map these operations to the ALU by standard architecture definitions.Note that the CPU is the whole chip; ALU is the specific sub-block.Therefore, the correct choice is ALU. Verification / Alternative check: 8085 block diagrams show the ALU connected to the accumulator and temporary registers, with status flag logic attached. Instruction manuals describe ALU actions per opcode. Why Other Options Are Wrong: CPU: Too broad; encompasses ALU plus control and registers. I/O: Handles external interfacing, not arithmetic/logic. bus decoder: Not a standard 8085 block name for ALU functions. flag controller: Flags reflect ALU outcomes; they do not compute results. Common Pitfalls: Using “CPU” and “ALU” interchangeably; forgetting that flags are a consequence of ALU operations, not a separate arithmetic unit. Final Answer: ALU

Question 10

Timing terminology — complete instruction execution: A(n) ________________ is the total time for a microprocessor to fetch, decode, and execute one complete instruction (including all required sub-cycles).

Accepted Answer

Introduction / Context: When analyzing performance or designing timing for peripherals, it is essential to distinguish between the overall instruction duration and the smaller bus activities that compose it. Textbooks and datasheets use precise terms to avoid confusion, especially with older microprocessors like the 8085 and 8086 families. Given Data / Assumptions: An instruction is executed via multiple steps: fetch, decode, execute, memory/IO accesses. Each memory or I/O access may constitute a machine cycle. The total time aggregates all sub-cycles needed for that instruction. Concept / Approach: The instruction cycle is the time required to complete one instruction from fetch to completion. It may consist of one or more machine cycles (for example, opcode fetch, memory read, memory write, I/O read/write). A single machine cycle is a lower-level bus transaction, while the instruction cycle is the higher-level envelope covering all machine cycles for that instruction. Step-by-Step Solution: Identify the required scope: “complete instruction.”Map sub-operations (fetch/execute) to one instruction envelope.Recognize that “machine cycle” is a subcomponent (e.g., one memory access).Select “instruction cycle” for the complete duration. Verification / Alternative check: 8085 timing charts show an instruction decomposed into multiple machine cycles, each further divided into T-states. Summing the machine cycles yields the instruction cycle time. Why Other Options Are Wrong: machine cycle: One memory/IO access; not necessarily the whole instruction. timing cycle: Vague term, not standard for a complete instruction. write cycle: A specific type of machine cycle. bus turnaround cycle: A bus arbitration concept; not the whole instruction. Common Pitfalls: Equating a single fetch with the entire instruction; ignoring additional read/write cycles for operands and results that extend the instruction cycle. Final Answer: instruction cycle

Question 11

Terminology — what do we call all programs for a computer? All computer programs, data files, and routines that run on a machine collectively fall under the category of ________.

Accepted Answer

Introduction / Context: Computer systems are commonly divided into hardware (the physical equipment) and software (the executable instructions and related data). Accurately using these terms matters, especially when differentiating between operating systems, applications, firmware, and microcode in troubleshooting or documentation. Given Data / Assumptions: We refer to general-purpose computers (PCs, embedded systems). “Programs” here include OS components and application code. We distinguish software from hardware and intermediate categories like firmware. Concept / Approach: Software encompasses all programs that can be stored, updated, and executed on hardware. Firmware is software stored in nonvolatile memory with a role close to hardware initialization/control. Hardware is the tangible device. Therefore, the umbrella term for all programs is “software.” Step-by-Step Solution: Determine whether the category should include OS and apps.Recognize that both are non-physical instruction sets.The collective term is “software.”Hence choose software. Verification / Alternative check: Standard computing texts define software as the ensemble of programs and related operational data, distinct from the hardware they control. Why Other Options Are Wrong: firmware: A specialized subset of software stored in ROM/Flash. hardware: Physical components; not programs. none of the above: Incorrect because “software” fits. microcode: Very low-level control store inside CPUs; not all programs. Common Pitfalls: Assuming firmware is not software; in fact, firmware is software with specific deployment characteristics. The general class remains software. Final Answer: software

Question 12

Programming levels — pure binary source: A program written entirely as strings of 0s and 1s for direct execution by the CPU is called a(n) ________.

Accepted Answer

Introduction / Context: Programs can be authored at different abstraction levels. At the lowest level, instructions are encoded in binary patterns that the CPU decodes directly. This question asks for the precise, standard term used in textbooks and processor manuals for such code. Given Data / Assumptions: Content consists exclusively of binary opcodes and operands. No symbolic mnemonics or labels are present in the source. The resulting file can be executed by the target CPU without translation. Concept / Approach: The canonical term is “machine language program,” also called “machine code.” It contrasts with assembly language programs (symbolic mnemonics to be assembled) and high-level programs (to be compiled or interpreted). While the phrase “binary program” is colloquially used, “binary language program” is not the standard formal label in curriculum or datasheets. Step-by-Step Solution: Identify that the code is CPU-ready bit patterns.Match this to the formal term “machine language program.”Exclude assembly (requires assembling) and interpreted (requires a runtime interpreter).Select the precise terminology for correctness and clarity. Verification / Alternative check: Introductory architecture texts consistently distinguish “machine language (machine code)” from “assembly language,” underscoring that machine code is already in executable binary form. Why Other Options Are Wrong: assembly language program: Requires assembly; not raw 0/1 code. interpreted program: Depends on an interpreter; description does not imply this. binary language program: Informal phrasing; not the standard technical term. macro program: A set of assembly macros; not relevant here. Common Pitfalls: Using “binary” as a generic label; while binaries are in 0s and 1s, the accepted term in instruction-set contexts is “machine language program.” Final Answer: machine language program

Question 13

Computer organization — “brains” of a microcomputer: Colloquially, the component referred to as the “brains” of every microcomputer is the ________ (the unit that fetches and executes instructions).

Accepted Answer

Introduction / Context: Public-facing explanations often call the central processing unit the “brains” of the computer because it coordinates the entire instruction execution process and orchestrates data movement. Even in microcomputer systems where the CPU is implemented as a single microprocessor chip (MPU), the conceptual role is still that of the CPU. Given Data / Assumptions: “Microcomputer” implies a system whose CPU is a microprocessor. We seek the broad, standard term used across computing education. The CPU includes the control unit, ALU, and registers from a functional perspective. Concept / Approach: The CPU fetches instructions, decodes them, controls the ALU operations, and manages registers and buses. Although “MPU” refers specifically to a microprocessor device that implements the CPU, the widely taught phrase “brains of the computer” maps to CPU, not to ROM, ALU alone, or peripheral controllers. Step-by-Step Solution: Identify the component responsible for overall instruction execution.Recognize CPU as the standard umbrella term.Differentiate CPU (system-wide role) from ALU (arithmetic sub-block) and ROM (storage).Choose CPU as the correct answer. Verification / Alternative check: Textbooks define CPU as comprising control logic and ALU, coordinating program execution. The microprocessor (MPU) is a physical implementation of the CPU on one chip in microcomputers. Why Other Options Are Wrong: ROM: Nonvolatile memory; stores programs but does not execute them. ALU: Performs arithmetic/logic but lacks overall control. MPU: A device form of CPU; the colloquial “brains” label refers to CPU’s role. DMA controller: Offloads memory transfers; not the central executor. Common Pitfalls: Equating ALU (a sub-block) with the entire CPU; assuming ROM’s program storage makes it the “brain.” Final Answer: CPU

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