Question 1

In a typical digital logic family, if Logic 0 spans 0 to 0.8 V, what voltage range is recognized as a valid Logic 1 level?

Accepted Answer

Introduction: Digital logic families define voltage thresholds for interpreting signals as Logic 0 (LOW) or Logic 1 (HIGH). Knowing these ranges ensures reliable interfacing and noise immunity. Given Data / Assumptions: Logic 0 (LOW) range: 0 to 0.8 V. We need the corresponding Logic 1 (HIGH) range in a typical 5 V logic system. Assume standard TTL-like thresholds where VIH(min) is near 2.0 V. Concept / Approach: Classic TTL specifies VIL(max) around 0.8 V and VIH(min) around 2.0 V, with VCC near 5 V. Thus, valid HIGH levels are typically any voltage from roughly 2.0 V up to VCC (about 5 V). Step-by-Step Solution: Identify VIL(max) = 0.8 V (given).Typical VIH(min) for TTL ≈ 2.0 V.Acceptable HIGH range ≈ 2.0 V to 5.0 V.Match with provided options: 2–5V. Verification / Alternative check: CMOS families at 5 V often use fractions of VCC, but TTL-compatibility commonly accepts ≥ 2.0 V as HIGH in mixed systems; 2–5V remains the broadly correct range here. Why Other Options Are Wrong: 2.5–5V: Too restrictive; 2.1 V or 2.2 V should still be HIGH in TTL-compatible inputs. 3.0–5.5V and 3.5–5.5V: Unrealistically high VIH(min); excludes valid HIGHs between 2 and 3 V. Common Pitfalls: Assuming all families use identical thresholds; always consult the specific datasheet. However, the 2–5 V convention remains a widely taught baseline for TTL levels. Final Answer: 2–5V

Question 2

In a positive logic system powered near 5 V, which voltage level commonly represents a HIGH (logic 1) state?

Accepted Answer

Introduction: Positive logic assigns higher voltages to logic 1 (HIGH) and lower voltages to logic 0 (LOW). In many introductory contexts, examples reference 5 V systems. Given Data / Assumptions: Positive logic convention. Nominal supply around 5 V, a common educational reference. We seek a typical HIGH level under this convention. Concept / Approach: In positive logic, logic 1 corresponds to a higher potential. With a 5 V supply, the canonical HIGH level is near +5 V, while 0 V corresponds to LOW. Real devices accept a range (e.g., ≥ 2.0 V for TTL), but +5 V is the archetypal level. Step-by-Step Solution: Positive logic: HIGH maps to higher voltage.With VCC ≈ 5 V, an idealized HIGH ≈ +5 V.Match the option stating +5 V. Verification / Alternative check: Thresholds vary by family (TTL/CMOS), but illustrative teaching uses +5 V for HIGH and 0 V for LOW in positive logic with 5 V rails. Why Other Options Are Wrong: 0 V: LOW in positive logic. +1 V: Below typical VIH(min); not reliably HIGH. +9 V: Exceeds the assumed 5 V system; not representative and may damage inputs. Common Pitfalls: Confusing positive logic mapping with exact VIH thresholds; the concept is mapping, not the precise datasheet limits. Final Answer: +5 V

Question 3

Express the fraction 1/4 as a binary fractional number (base-2 representation).

Accepted Answer

Introduction: Binary fractions represent values to the right of the binary point using negative powers of 2. Converting a rational fraction such as 1/4 illustrates how place values work in base 2. Given Data / Assumptions: Fraction to convert: 1/4. Binary fractional places represent 1/2, 1/4, 1/8, etc. No rounding required; 1/4 is exactly representable. Concept / Approach: The first place to the right of the binary point is 2^-1 = 1/2, the second is 2^-2 = 1/4, the third is 2^-3 = 1/8, and so on. To represent 1/4 exactly, set the 2^-2 place to 1 and the others to 0. Step-by-Step Solution: List binary place values: 0.1 = 1/2, 0.01 = 1/4, 0.001 = 1/8.Identify 1/4 = 2^-2.Set only the 2^-2 position to 1.Binary representation: 0.01₂ = 1/4. Verification / Alternative check: Compute value of 0.01₂ = 0*(1/2) + 1*(1/4) = 1/4. Exact match, no remainder. Why Other Options Are Wrong: 0.11 = 1/2 + 1/4 = 3/4. 0.10 = 1/2. 0.00 = 0. Common Pitfalls: Misreading positions to the right of the point; remember each step halves the weight: 1/2, 1/4, 1/8, etc. Final Answer: 0.01

Question 4

In pulse and timing measurements, the rise time of a digital pulse is normally measured between which reference levels?

Accepted Answer

Introduction: Rise time characterizes how quickly a signal transitions from LOW to HIGH. Consistent reference levels avoid distortion from overshoot, noise, and edge rounding across technologies. Given Data / Assumptions: We need the conventional measurement points for rise time on a single transition. Assume a monotonic leading edge with possible overshoot or rounding. Concept / Approach: Industry convention defines rise time as the interval between when the waveform first crosses 10% of its final value and when it first crosses 90% of its final value. This avoids sensitivity to baseline noise near 0% and to final settling near 100%. Step-by-Step Solution: Identify standard reference points: 10% and 90% of final amplitude.Measure time of first crossing at 10%.Measure time of first crossing at 90%.Rise time = t(90%) - t(10%). Verification / Alternative check: Some instruments allow 20–80% as an alternative, but 10–90% is the canonical definition used for datasheets and comparisons. Why Other Options Are Wrong: 0 and 100%: Too sensitive to noise and settling behavior. 30% and 70%: Non-standard; sometimes used in specific contexts but not the primary convention. 50% to 50% (leading to trailing): That is pulse width, not rise time. Common Pitfalls: Confusing rise time with propagation delay or pulse width; always check which metric and thresholds are specified. Final Answer: 10% and 90% level

Question 5

In digital circuit terminology, the manner in which a circuit responds to its inputs (mapping inputs to outputs) is called its ________. Identify the correct term.

Accepted Answer

Introduction: Digital circuits implement specific relationships between inputs and outputs. The formal description of this input-output mapping is central to analysis, design, and verification. Given Data / Assumptions: We refer to the functional behavior of a circuit, not its physical construction. Inputs and outputs are signal variables; the mapping between them is the focus. Concept / Approach: The term “logic” (or logic function) denotes the rule set defining outputs for each input combination. It may be represented by truth tables, Boolean expressions, or logic diagrams. Wiring and physical layout do not by themselves define the functional mapping; they realize it physically. Step-by-Step Solution: Identify the sought concept: functional mapping from inputs to outputs.Associate that mapping with Boolean algebra representations.Select the term “logic.” Verification / Alternative check: A truth table enumerates the circuit's logic. Simplified Boolean forms (e.g., SOP or POS) also specify the logic equivalently. Why Other Options Are Wrong: Wiring: Refers to physical interconnections, not the abstract function. Inputs: These are variables, not the behavior. Outputs: These are results, not the rule that produces them. Common Pitfalls: Confusing implementation (gates, wiring, timing) with specification (logic). Timing adds constraints but the logic defines the functional correctness. Final Answer: logic

Question 6

When a system defines a HIGH voltage as binary 0 and a LOW voltage as binary 1, what is this logic convention called?

Accepted Answer

Introduction: Logic conventions determine how physical voltages map to logical values. Two common conventions are positive logic and negative logic, which invert the mapping relative to each other. Given Data / Assumptions: HIGH voltage is assigned to binary 0. LOW voltage is assigned to binary 1. We are asked to name this convention. Concept / Approach: In positive logic, HIGH corresponds to 1 and LOW to 0. In negative logic, the mapping is reversed: HIGH corresponds to 0 and LOW corresponds to 1. Therefore, the described mapping is negative logic. Step-by-Step Solution: Identify mapping: HIGH -> 0, LOW -> 1.Compare with definitions: positive vs negative logic.Recognize inversion relative to positive logic.Select “negative logic.” Verification / Alternative check: Truth tables under negative logic can be transformed to positive logic by complementing signals and reinterpretation; functional behavior remains consistent when conventions are applied uniformly. Why Other Options Are Wrong: Positive logic: Opposite mapping (HIGH = 1). Invalid logic: The convention is valid; it is a defined alternative. Assertion-level logic: Refers to active-high or active-low signaling semantics, not the global numeric mapping itself. Common Pitfalls: Assuming negative logic is “wrong.” It is legitimate and often used in active-low control signals (e.g., enable_n). Final Answer: negative logic

Question 7

Microprocessor vs. dedicated controller: A microprocessor that is designed to handle only specific, dedicated control tasks in an embedded system is also called a ________.

Accepted Answer

Introduction / Context: Digital electronics and computer architecture distinguish between general-purpose CPUs and specialized controllers. This question tests whether you know the term used for a processor that handles narrowly defined, dedicated control tasks in embedded products like appliances, vehicles, and IoT devices. Given Data / Assumptions: Device focuses on specific, dedicated tasks. Context is embedded system control, not full-scale desktop computing. We need the standard industry term. Concept / Approach: The correct term for a processor packaged with on-chip program memory, data memory, and I/O peripherals intended for dedicated control is “microcontroller.” A general-purpose microprocessor typically requires external memory and peripherals and targets broad computing workloads. Step-by-Step Solution: Step 1: Identify that the workload is fixed-function and embedded.Step 2: Map fixed-function control to the component class that integrates CPU + memory + peripherals.Step 3: The industry-standard name is microcontroller (often abbreviated MCU). Verification / Alternative check: Check typical examples: 8051, AVR, PIC, ARM Cortex-M families are microcontrollers used in appliances, toys, and automotive control. These are not marketed as general-purpose laptop/desktop CPUs. Why Other Options Are Wrong: Calculator: An application device, not a processor class.Laptop microcomputer: A complete system for general-purpose tasks, not a dedicated controller.Workstation processor: High-performance general-purpose CPU, not embedded-focused.Digital signal analyzer: A measurement instrument, not a controller class. Common Pitfalls: Confusing “microprocessor” and “microcontroller” because both contain a CPU core. The key difference is integration and target use: microcontrollers integrate memory/peripherals for embedded control. Final Answer: microcontroller

Question 8

Communication mode in the referenced figure (assume a single-wire, time-sequenced bit stream typical of UART links): The systems communicate using ________.

Accepted Answer

Introduction / Context: When a figure is referenced but unavailable, we apply the recovery policy by making a minimal, standard assumption: a typical two-device link using a single signal line with time-sequenced bits suggests a serial interface (e.g., UART). Given Data / Assumptions: No figure provided; assume a common UART-like link. Two endpoints exchange bits over a limited set of conductors. Goal: identify the data communication mode. Concept / Approach: Serial data sends one bit after another over one channel or pair; parallel sends multiple bits simultaneously over multiple lines. A minimal two- or three-wire link (TX, RX, GND) strongly implies serial. Step-by-Step Solution: Step 1: Infer wiring simplicity from the assumption (few lines).Step 2: Map few lines + time sequencing to serial data.Step 3: Conclude “serial data” as the communication mode. Verification / Alternative check: Common serial standards (UART, RS-232, RS-485, SPI, I2C) minimize conductors compared to parallel buses which need a data bus width plus control lines. Why Other Options Are Wrong: Parallel data: Requires many data lines; unlikely under the minimal-wiring assumption.Serial-parallel hybrid data: Not standard terminology for a basic two-node link.Optical time-division bus: Too specific and not implied by a simple two-wire assumption.Current-loop multidrop: A niche physical layer (e.g., 20 mA loops) not implied here. Common Pitfalls: Assuming parallel simply because two devices are connected. Without a wide ribbon of data lines or bus control signals, parallel is unlikely. Final Answer: serial data

Question 9

Computer organization basics: A(n) ________ is not a functional unit of a computer.

Accepted Answer

Introduction / Context: Functional units of a basic computer are the standardized architectural blocks that enable input, processing, storage, and control. This question checks recognition of what is and is not a core functional unit. Given Data / Assumptions: Standard textbook model: input, output, memory, ALU, and control. We must choose the item that is not one of these core units. Concept / Approach: The classic Von Neumann view includes input unit, output unit, memory unit, ALU, and control unit. A modem is an external communication device/peripheral, not a core functional unit. Step-by-Step Solution: Step 1: List canonical functional units: input, output, memory, ALU, control.Step 2: Compare options to the canonical list.Step 3: Identify “modem” as a communication peripheral rather than a core unit. Verification / Alternative check: Intro CS and architecture texts categorize modem as an I/O device on communication interfaces, not an internal architectural unit like the ALU or control unit. Why Other Options Are Wrong: Input unit: Core unit for data ingress.Memory unit: Core for storage of instructions/data.Control unit: Core for sequencing and control signals.Arithmetic-logic unit: Core for arithmetic/logic operations. Common Pitfalls: Equating frequently used peripherals (like modems) with functional units. Functional units are architectural blocks, not external devices. Final Answer: modem

Question 10

Display interfacing: A binary number can be converted to a 7-segment display pattern by using a(n) ________.

Accepted Answer

Introduction / Context: Seven-segment displays require segment control signals (a–g). Converting a binary code (often BCD) into segment lines is a classic display-interface problem. Given Data / Assumptions: Input: binary/BCD code for a digit. Output: seven segment control lines. Goal: identify the digital block that performs this mapping. Concept / Approach: A decoder maps an encoded input into a set of outputs; a BCD-to-7-segment decoder asserts the correct segment lines for each digit. An encoder does the reverse (many inputs to coded output). Step-by-Step Solution: Step 1: Recognize the direction: code → many segment lines.Step 2: This is a decode operation.Step 3: Choose “decoder.” Verification / Alternative check: Standard ICs like 7447/7448 (TTL) are BCD-to-7-segment decoders/drivers, confirming the mapping role. Why Other Options Are Wrong: Encoder: Opposite direction (many lines to fewer coded bits).Multiplexer: Selects one of many inputs to a single output; not direct code-to-segment mapping.Magnitude comparator: Compares numbers; does not generate segment codes.Priority encoder: Still an encoder, not a decoder. Common Pitfalls: Confusing encoder vs. decoder directionality. Final Answer: decoder

Question 11

Terminology check: In digital design, complete systems that operate on two discrete levels are often called ________.

Accepted Answer

Introduction / Context: Digital systems process information using discrete voltage levels (commonly interpreted as 0 and 1). This question checks familiarity with common terminology for such systems. Given Data / Assumptions: Two-level operation is implied. We want the standard, widely used term. Concept / Approach: Because the information is represented using two symbols, these systems are routinely called “binary systems.” They are also discussed within “logic systems,” but “numbering systems” and “ADC systems” refer to different ideas. Step-by-Step Solution: Step 1: Identify that the system uses two discrete states.Step 2: Map two-state representation to “binary.”Step 3: Select “binary systems.” Verification / Alternative check: Textbooks frequently denote digital circuits as binary logic circuits and digital systems as binary systems because they encode data in base-2. Why Other Options Are Wrong: Logic systems: Close in meaning, but the standard term highlighting two-level representation is “binary systems.”Numbering systems: A broader mathematical topic (binary, octal, decimal, hexadecimal).ADC systems: Concern conversion of analog signals to digital, not the general name for digital systems.Analog threshold systems: Not standard terminology for digital systems. Common Pitfalls: Equating “logic systems” (a valid phrase) with the more precise “binary systems” when the emphasis is specifically on two discrete levels. Final Answer: binary systems

Digital Concepts Questions