Question 1

Even-parity check: For the 9-bit data word 100111100, determine whether an even-parity system with parity bit = 0 is a correct combination (i.e., total number of 1s must be even).

Accepted Answer

Introduction / Context: Parity bits provide simple error detection. In an even-parity system, the total count of 1s across the data bits plus the parity bit must be even. Verifying parity requires counting ones accurately and checking whether the parity setting produces an even total. Given Data / Assumptions: Data word: 100111100 (9 bits). Parity scheme: even parity. Proposed parity bit value: 0. Concept / Approach: Count the number of 1s in the data. If the count is odd, the parity bit must be 1 to make the total even; if the count is even, the parity bit should be 0. This is independent of byte ordering or endianness since parity is a scalar property of the bit set. Step-by-Step Solution: Write data: 1 0 0 1 1 1 1 0 0.Count ones: positions 1, 4, 5, 6, 7 → total = 5.Even parity requires total ones (data + parity) to be even.With parity bit = 0, total remains 5 (odd) → parity condition not met. Verification / Alternative check: Set parity bit = 1 instead: total would be 6 (even), which would satisfy even parity. Why Other Options Are Wrong: Correct: Fails because 5 ones + 0 parity is odd.Odd parity reference / Depends on endianness: The scheme is explicitly even parity; endianness does not affect the count of ones. Common Pitfalls: Miscounting ones in longer bit strings.Confusing odd vs. even parity conventions. Final Answer: Incorrect

Question 2

Combinational logic terminology: In multiplexing, a “data selector” refers to a circuit that routes one of many data inputs to a single output. Is it correct to say that a data selector is the same as a demultiplexer?

Accepted Answer

Introduction / Context: Digital designers often use the terms multiplexer (MUX), demultiplexer (DEMUX), and data selector. While they sound similar, they describe different signal-routing functions. This question checks whether you can distinguish a “data selector” (another common name for a multiplexer) from a demultiplexer, which performs the opposite routing direction. Given Data / Assumptions: “Data selector” is a term used in many datasheets for multiplexers. A multiplexer selects one of N inputs and forwards it to a single output using select lines. A demultiplexer takes a single input and routes it to one of N outputs, chosen by select lines. Concept / Approach: The core difference is the direction of data flow with respect to fan-in/fan-out. A multiplexer has many inputs and one output (many-to-one). A demultiplexer has one input and many outputs (one-to-many). Both use select lines, but their roles are inverse. Therefore, a “data selector” is not a demultiplexer; it is a multiplexer. Step-by-Step Solution: Identify what a data selector does: route one of many inputs to one output.Compare with a demultiplexer: take one input and steer it to one of many outputs.Note that the select logic looks similar but the signal direction is opposite.Conclude: data selector ≡ multiplexer, not demultiplexer. Verification / Alternative check: Check classic parts: 74HC151 is titled “8-channel data selector/multiplexer” (8-to-1 MUX). Demultiplexer examples include 74HC138/139 used in address decoding (1-to-8 or 1-to-4 demux-like functions). The nomenclature in vendor datasheets confirms the distinction. Why Other Options Are Wrong: Correct: Would imply data selector equals demultiplexer, which is not the case. Only correct for active-LOW devices: Signal polarity does not change the fundamental function. Only correct when tri-stated / Applies only to analog switches: Tri-state or analog implementation details do not redefine MUX vs. DEMUX roles. Common Pitfalls: Assuming symmetric interchangeability due to similar select lines; overlooking that many IC titles explicitly pair “data selector” with “multiplexer.” Final Answer: Incorrect

Question 3

Addressing inputs with select lines: In a standard multiplexer, how many select lines are required to uniquely address four (4) data input lines?

Accepted Answer

Introduction / Context: Multiplexers use select lines to choose which one of several inputs is connected to the output. Understanding the relationship between the number of inputs and the number of select lines is a basic but essential skill in combinational logic design. Given Data / Assumptions: Number of inputs N = 4. Binary addressing via select lines. Standard MUX behavior, independent of the specific logic family. Concept / Approach: The number of select lines k needed to address N inputs satisfies N = 2^k. Solving for k gives k = log2(N). Thus, for N = 4, k = log2(4) = 2. Therefore, two select lines (commonly labeled S1 and S0) are sufficient and necessary to address four inputs. Step-by-Step Solution: Given N = 4 inputs.Compute k = log2(4) = 2.Assign select lines S1, S0 producing address codes 00, 01, 10, 11 to select inputs I0–I3.Conclude that exactly two select lines are required. Verification / Alternative check: Examine a 74HC153 (dual 4-to-1 MUX): two select lines select among four inputs for each section, confirming the theoretical relationship. Why Other Options Are Wrong: Three select lines: 3 lines give 2^3 = 8 addresses, excessive for 4 inputs. Depends only on logic family: The relation N = 2^k is universal. Needs four select lines due to enable: Enable pins do not count as select lines for addressing inputs. “Incorrect (three select lines are not required)”: while true as a comment, it does not answer with the needed count; the correct quantitative choice is two lines. Common Pitfalls: Confusing enable/strobe pins with select lines; assuming one select per input instead of binary addressing. Final Answer: Requires two select lines (S1, S0)

Question 4

Decoder vs. encoder: A digital circuit that converts coded information into a familiar, human-readable, or non-coded form (such as driving a display) is called an ________.

Accepted Answer

Introduction / Context: Two fundamental blocks in digital systems are encoders and decoders. Although their names sound similar, they perform inverse operations. Correctly identifying which circuit expands a coded input into a familiar or non-coded output (such as segment lines for displays) is crucial when interfacing with human-readable devices. Given Data / Assumptions: “Coded information” means a compact representation (e.g., BCD or binary). “Familiar/non-coded form” often refers to line patterns like seven-segment outputs. We are considering basic combinational blocks (no memory). Concept / Approach: An encoder compresses many input lines into a smaller coded output (e.g., 8-to-3). A decoder expands a coded input into many outputs or a display-friendly format (e.g., 3-to-8 decoder, BCD-to-7-segment driver). Therefore, a circuit that takes coded input and produces a human-recognizable output is a decoder. Step-by-Step Solution: Interpret “coded input” as binary or BCD.Map to outputs that directly drive indicators (e.g., LED segments).Recognize the one-to-many expansion characteristic of a decoder.Select “decoder” as the correct term. Verification / Alternative check: Typical ICs like 74HC138 (3-to-8 decoder) or 74HC4511 (BCD-to-7-segment decoder/driver) demonstrate taking a compact code and driving many output lines for display or selection, confirming the function is decoding. Why Other Options Are Wrong: Encoder: Performs the reverse (many inputs to fewer coded outputs). Buffer, multiplexer, latch: Serve other roles (drive strength, selection among inputs, or storage) rather than code expansion for display. Common Pitfalls: Confusing the “direction” of information (compression vs. expansion); assuming any display driver is an encoder when it is typically a decoder/driver. Final Answer: decoder

Question 5

Logic family numbering: In 54/74-series logic ICs, the “54” prefix denotes an extended (military) operating temperature range compared to the “74” commercial range. Is this statement accurate?

Accepted Answer

Introduction / Context: Classic logic families are identified by series numbers such as 54xx and 74xx. Understanding the differences helps engineers select parts that will operate reliably across required environmental conditions, especially in aerospace and defense applications. Given Data / Assumptions: 54-series devices are qualified for extended temperature ranges. 74-series devices are targeted at commercial/industrial ranges depending on suffix. The underlying logic family (TTL, CMOS derivatives) can exist under both prefixes. Concept / Approach: The “54” prefix historically indicates military-grade temperature specifications (for example, approximately −55 °C to +125 °C), tighter screening, and sometimes different packaging options. The “74” series typically denotes commercial or industrial temperature ranges depending on specific family variants and manufacturer datasheets. Step-by-Step Solution: Identify the prefix (54 vs. 74) on a given logic part number.Recall the associated operating temperature ranges and qualification level.Confirm that “54” corresponds to extended/military environments.Conclude the statement is accurate. Verification / Alternative check: Cross-reference vendor datasheets: 54HCxx or 54LSxx lines list wider temperature specs versus 74HCxx or 74LSxx commercial counterparts, validating the role of the prefix. Why Other Options Are Wrong: Incorrect/Only for CMOS/Only for high-speed/Only for plastic: The prefix denotes qualification range regardless of whether the family is TTL or CMOS and is not bound to speed grade or package type alone. Common Pitfalls: Equating “74” exclusively with commercial 0–70 °C without noting industrial variants; overlooking the fact that both prefixes can cover multiple sub-families with different electrical characteristics. Final Answer: Correct

Question 6

Using XOR as a controlled inverter: An exclusive-OR gate will invert the signal on one input if the other input is held permanently HIGH. Is this behavior correct?

Accepted Answer

Introduction / Context: The exclusive-OR (XOR) gate is a versatile building block. One practical use is as a conditional inverter: by tying one input to a control level, the XOR either passes the signal through unchanged or inverts it. This capability appears frequently in digital signal conditioning and simple arithmetic circuits. Given Data / Assumptions: Two-input XOR gate under positive logic. One input is held at logic HIGH (1). The other input is the signal of interest. Concept / Approach: The XOR truth rule is A XOR B = 1 when A ≠ B and 0 when A = B. If one input is fixed at 1, the output becomes the logical NOT of the other input because output is 1 exactly when the other input is 0, and 0 when it is 1. Thus, tying an XOR input high converts the gate into an inverter for the remaining input. Step-by-Step Solution: Let control input C = 1; signal input S varies.Compute output: Y = S XOR C.With C = 1, Y = NOT S (since XOR with 1 inverts).Therefore, the XOR acts as a controlled inverter. Verification / Alternative check: Similarly, if the control input C = 0, XOR passes the signal through (Y = S). This dual behavior allows simple “invert enable” functions in designs without adding a separate NOT gate. Why Other Options Are Wrong: Incorrect/conditional options: The XOR identity holds across logic families and frequencies within normal operating limits; it is a fundamental truth-table property, not a timing artifact. Common Pitfalls: Confusing XOR with OR (where tying one input HIGH forces constant HIGH); forgetting that XOR with 1 toggles, with 0 passes-through. Final Answer: Correct

Question 7

Canonical SOP restriction: In a true sum-of-products (SOP) expression, inversion (complement) bars apply to individual variables only, not across sums of variables. Is this statement valid for canonical SOP forms?

Accepted Answer

Introduction / Context: Boolean expressions can be written in different canonical and standard forms, notably sum-of-products (SOP) and product-of-sums (POS). Understanding how complements appear in each form helps prevent algebraic mistakes and leads to correct gate-level implementations. Given Data / Assumptions: We are discussing true or canonical SOP, where each product term is a conjunction of literals. A literal is either a variable (e.g., A) or its complement (A’). No overbar should span a sum inside an SOP product term. Concept / Approach: In SOP, each term is an AND of literals, and the overall function is an OR of those terms. Complements apply to individual variables within product terms, not to grouped sums. An overbar spanning a sum indicates a complemented sum, which belongs to POS or requires application of De Morgan’s theorems to return to SOP. Step-by-Step Solution: Recognize SOP structure: F = T1 + T2 + ... where each Ti = literal * literal * ...Identify that literals can be A or A’ but not (A + B)’ within a product term.If you find (A + B)’ inside a product, apply De Morgan: (A + B)’ = A’ * B’ to restore SOP.Conclude the original statement is valid for canonical SOP. Verification / Alternative check: Construct a Karnaugh map and derive the minimal SOP. The grouped cells correspond to product terms with complements on variables only, never complemented sums within a product term. Why Other Options Are Wrong: Incorrect/conditional options: The rule is general to SOP structure, independent of the number of variables or gate technology. Common Pitfalls: Mixing SOP and POS conventions; placing bars over entire parentheses in SOP; forgetting to transform complemented sums using De Morgan’s laws. Final Answer: Correct

Question 8

Truth tables in logic design: A truth table is an effective way to enumerate every possible combination of independent input variables and record the corresponding output(s). Is this statement accurate?

Accepted Answer

Introduction / Context: Truth tables are foundational tools for describing and analyzing combinational logic. They provide a complete mapping from inputs to outputs, supporting tasks such as deriving Boolean expressions, verifying designs, and generating test patterns. Given Data / Assumptions: Independent input variables are binary (0/1). All 2^n combinations are listed for n inputs. Outputs are recorded for each input combination. Concept / Approach: A truth table exhaustively covers the input space. With n independent binary inputs, there are exactly 2^n rows. Each row specifies the system’s deterministic output(s). This approach is applicable to both simple gates and larger combinational networks and is the basis for Karnaugh maps and algorithmic minimization. Step-by-Step Solution: Identify the number of inputs n.Create 2^n rows covering all input combinations.Compute or specify outputs for each row (by gate logic or function).Use the table to derive or verify Boolean expressions as needed. Verification / Alternative check: Karnaugh maps are a rearranged visualization of the same exhaustive enumeration, preserving adjacency properties for simplification. Automated tools similarly rely on exhaustive enumeration for small n or symbolic methods for larger n. Why Other Options Are Wrong: Incorrect/limited cases: Truth tables are not restricted to two inputs, nor specific coding schemes; they apply broadly to combinational logic (sequential logic requires state tables but still uses tabular methods). Common Pitfalls: Omitting combinations due to oversight; confusing truth tables with state transition tables for sequential systems; not maintaining consistent input ordering which complicates debugging. Final Answer: Correct

Question 9

Exclusive-NOR (XNOR) identity: Which Boolean expression correctly represents the two-input exclusive-NOR function?

Accepted Answer

Introduction / Context: Exclusive-NOR (XNOR) outputs HIGH when its inputs are equal (both 0 or both 1) and LOW when they differ. Recognizing its Boolean identity is essential for algebraic manipulation, schematic implementation, and verification against truth tables or Karnaugh maps. Given Data / Assumptions: Two-input function under positive logic. Goal is to match a standard Boolean expression to XNOR behavior. Complement notation: X′ denotes NOT X. Concept / Approach: The definition “equal → HIGH” translates directly to the sum of the two equal cases: A = 0, B = 0 and A = 1, B = 1. In minterm form, these are A′B′ and AB. Therefore, XNOR = A′B′ + AB. The complement of this (A′B + AB′) is the XOR function (different → HIGH). Step-by-Step Solution: List truth table rows where output should be 1: (A,B) = (0,0) and (1,1).Write minterms: A′B′ and AB.Sum the minterms: F = A′B′ + AB.Conclude that this is the XNOR identity. Verification / Alternative check: Karnaugh map placement of the 1s at (00) and (11) groups to yield A′B′ + AB; algebraically, note that XNOR = (A ⊙ B)′ = (A′B + AB′)′ which by De Morgan simplifies to A′B′ + AB. Why Other Options Are Wrong: A′B + AB′: This is XOR (different → HIGH). (A + B) * (A′ + B′): Expands to A′B + AB′ (also XOR), not XNOR. A + B: Ordinary OR gate, 00 yields 0 not 1. AB′ + A′: Not symmetric and does not match the equality condition. Common Pitfalls: Mixing up XOR and XNOR; forgetting that XNOR is the complement of XOR and represents equality; misapplying De Morgan transformations. Final Answer: A′B′ + AB

Question 10

Programming control flow basics: When a decision requires choosing between exactly two possible actions, the IF / THEN / ELSE control structure is the appropriate construct. Is this statement correct?

Accepted Answer

Introduction / Context: Control flow structures are fundamental across programming and hardware description languages. The IF / THEN / ELSE construct is the canonical way to select between two mutually exclusive actions based on a Boolean condition, and it appears in languages from C and Python to VHDL and Verilog (with syntactic variations). Given Data / Assumptions: The decision space comprises exactly two branches (do one thing or the other). A Boolean predicate determines which branch to take. The discussion is language-agnostic in principle. Concept / Approach: The IF / THEN / ELSE pattern evaluates a condition. If true, the THEN branch executes; otherwise, the ELSE branch executes. This ensures precisely one of the two paths is taken, making it ideal for binary decisions. In HDL, similar structures (if/else, conditional signal assignments) implement two-way choice in concurrent or sequential contexts. Step-by-Step Solution: Identify the decision predicate (e.g., X > 0).Use IF to test the predicate.Under THEN, implement action A; under ELSE, implement action B.Guarantee only one action runs per evaluation, matching two-way branching needs. Verification / Alternative check: Compare with CASE/ switch constructs which are better for multi-way branching; IF / THEN / ELSE remains the simplest and most readable for precisely two alternatives. Ternary operators (e.g., C’s ?: or HDL conditional assignments) are syntactic shorthands for the same two-branch logic. Why Other Options Are Wrong: Incorrect / Only for assembly / Only for HDL / Only if conditions are mutually exclusive: IF / THEN / ELSE is universal; mutual exclusivity is inherent because the ELSE branch is the complement of the IF condition. Common Pitfalls: Nesting multiple two-way decisions where a CASE would be clearer; writing overlapping conditions that inadvertently make both branches reachable (resolved by proper Boolean formulation). Final Answer: Correct

Question 11

Dual in-line package (DIP) pin-numbering convention: Evaluate the rule-of-thumb: “If you place the notch to your right, pin 1 will always be in the lower-right corner.” Clarify correct DIP orientation and numbering.

Accepted Answer

Introduction / Context: DIP (dual in-line package) integrated circuits use a standardized pin-numbering scheme. Knowing where pin 1 is helps prevent reversed installation, board damage, and miswiring. The prompt suggests a rule-of-thumb that placing the notch to the right puts pin 1 at the lower-right corner. This statement is widely contrary to standard orientation and therefore must be evaluated critically. Given Data / Assumptions: Standard DIP viewed from the top (markings facing you). A notch or a dot indicates the pin-1 end. Numbering proceeds counterclockwise around the package when viewed from the top. Concept / Approach: With the notch at the top, pin 1 is the top-left lead, and numbers increase down the left side, across the bottom, and back up the right side to the top-right for the highest pin number. Rotating the package changes which physical corner appears “lower-right,” but pin-1 location is always determined by the notch/dot and the counterclockwise sequence, not by a “notch-right means lower-right” shortcut. Step-by-Step Solution: Place the DIP so that the notch is at the top (conventional orientation).Identify pin 1 at the upper-left corner.Proceed counterclockwise: down the left side to the bottom-left corner, then along the bottom to bottom-right, then up the right side to the top-right (highest pin number).Therefore, “notch to the right → pin 1 lower-right” is not a valid general rule. Verification / Alternative check: Most datasheets show the counterclockwise top-view numbering and mark pin 1 with a dot or notch. This universal convention supersedes ad-hoc mnemonics. Why Other Options Are Wrong: Correct: Conflicts with the universal counterclockwise convention.Applies only to 40-pin DIP: Pin-1 convention is package-agnostic.Depends on socketing: Socket presence does not change pin numbering. Common Pitfalls: Using board orientation rather than package markings; ignoring the dot near pin 1; confusing top-view with bottom-view diagrams. Final Answer: Incorrect

Question 12

Parity basics in digital communications: In an even-parity system, the parity bit is chosen so that the total number of 1s (data bits + parity) is even. Evaluate this statement.

Accepted Answer

Introduction / Context: Parity is a classic error-detection method used in serial links, memory systems, and storage. “Even parity” and “odd parity” describe how the parity bit is set to make the overall count of logical 1s either even or odd. Understanding this helps interpret UART frames, memory parity errors, and simple link diagnostics. Given Data / Assumptions: Even-parity scheme is employed. Data word length may vary (e.g., 7 or 8 bits), but the rule is independent of length. Only single-bit parity (one parity bit) is considered. Concept / Approach: Definition: In an even-parity system, if the data bits contain an odd number of 1s, the parity bit is set to 1 to make the total even; if the data bits already contain an even number of 1s, the parity bit is set to 0. This gives a quick way to detect any odd number of bit flips. Step-by-Step Solution: Count the number of 1s in the data word.If count is even → set parity bit = 0; total ones remains even.If count is odd → set parity bit = 1; total ones becomes even.Hence the statement aligns exactly with the standard definition. Verification / Alternative check: Test with an example: data 10110010 has four 1s (even), so parity = 0 and overall ones remain even. Flip one data bit and parity detection flags a mismatch. Why Other Options Are Wrong: Incorrect: Contradicts the definition of even parity.Only true for 7-bit ASCII: Parity rule is independent of word size.Depends on baud rate: Parity logic is independent of signaling speed. Common Pitfalls: Confusing the terms “even” and “odd”; counting bits incorrectly; assuming parity corrects errors (it only detects many, not all). Final Answer: Correct

Question 13

Odd-parity validation example: For an ODD-parity system, consider data = 011011100 (9 bits). With parity bit = 0, does the word pass an odd-parity check? Evaluate.

Accepted Answer

Introduction / Context: Parity schemes append one extra bit to help detect transmission errors. In an odd-parity system, the total number of 1s in the complete word (data + parity) must be odd. We check whether a given data word paired with a stated parity bit satisfies this rule. Given Data / Assumptions: Data bits: 011011100. Parity type: odd parity. Parity bit provided: 0. Concept / Approach: Count the number of 1s in the data. If the count is already odd, then an odd-parity bit of 0 keeps the total odd. If the count is even, the parity bit must be 1 to make the total odd. Step-by-Step Solution: Count ones in 011011100 → ones at positions 2,3,5,6,7 = 5 ones.Five is odd, so to maintain odd parity, parity bit should be 0.Total ones including parity = 5 + 0 = 5 (still odd).Therefore, the provided combination passes an odd-parity check. Verification / Alternative check: If one data bit flips (e.g., to 011011101), ones become 6; with parity 0 total is 6 (even) and the checker flags an error. Why Other Options Are Wrong: Incorrect: Miscounts ones or misapplies odd-parity rule.Valid only if start/stop bits are ignored: Framing bits are not part of the payload parity in typical UART schemes.Cannot be determined: Sufficient information is provided (data and parity). Common Pitfalls: Off-by-one in counting ones; confusing even vs odd parity; mixing parity with checksums/CRCs. Final Answer: Correct

Question 14

Structured decision making in HDL/pseudocode: “When one of many possible actions may be taken, the ELSIF (else-if) control structure is used.” Evaluate this guidance.

Accepted Answer

Introduction / Context: Digital system descriptions (HDL, firmware pseudocode) need multi-branch control structures to select among alternatives. Two common patterns are chained IF/ELSIF/ELSE and CASE statements. Understanding when ELSIF is appropriate helps write clear and synthesizable code. Given Data / Assumptions: Multiple mutually exclusive conditions must be evaluated in sequence. ELSIF is available (e.g., VHDL elsif, many languages else if). CASE may also be available when testing one expression against discrete values. Concept / Approach: ELSIF is suited for priority-ordered decision chains where each condition can be a general Boolean expression. CASE is preferred when switching on a single expression with a list of discrete matches. The statement claims ELSIF is used when one of many actions may be needed; that is accurate for general multi-branch logic. Step-by-Step Solution: Identify that more than two outcomes are possible.Use IF for the first condition; use ELSIF for additional conditions; finalize with ELSE for the default path.Ensure mutual exclusivity or priority as required by design. Verification / Alternative check: Compare to a CASE statement: if all branches are simple equality checks of a single selector value, CASE can be clearer. Otherwise, chained IF/ELSIF is the right tool. Why Other Options Are Wrong: Incorrect: ELSIF is indeed a standard pattern for many-choice logic.Only true in flowcharts: ELSIF is a code construct, not just a diagramming concept.Only for two-way decisions: That would be IF/ELSE; ELSIF indicates more than two options. Common Pitfalls: Overusing CASE when complex conditions exist; forgetting a final ELSE for completeness; overlapping conditions causing unreachable branches. Final Answer: Correct

Question 15

Gate naming conventions: Confirm whether the standard abbreviation for the exclusive-OR gate is “XOR.”

Accepted Answer

Introduction / Context: Across textbooks, datasheets, and CAD libraries, consistent abbreviations help engineers interpret schematics quickly. The exclusive-OR function is pervasive in adders, parity circuits, and comparators, so its standardized shorthand is important. Given Data / Assumptions: Exclusive-OR is a logic operation with symbol often drawn as OR with an additional curved line. Written symbols include the circle-plus and alphabetic abbreviations. Concept / Approach: “XOR” is the widely adopted abbreviation for exclusive-OR in signal names (e.g., XOR2), IP block names, and HDL code comments. Alternatives like “EOR” appear historically, but XOR is dominant in digital design practice. Step-by-Step Solution: Identify the logic operation: exclusive-OR.Check common usage in literature and toolchains: XOR.Conclude that the statement is correct. Verification / Alternative check: Look at HDL operators: in many languages, the caret ^ denotes XOR, and library cell names include “XOR.” Why Other Options Are Wrong: Incorrect: Conflicts with standard practice.Only valid in arithmetic circuits: XOR is fundamental logic, not limited to arithmetic contexts.Depends on manufacturer: Minor variations exist, but XOR remains standard. Common Pitfalls: Confusing XOR with OR; misreading XNOR (exclusive-NOR) as XOR. Final Answer: Correct

Question 16

Definition check for even parity: “Even parity means that each protected group of bits (data plus parity) contains an even number of 1s.” Evaluate this statement.

Accepted Answer

Introduction / Context: Parity is a simple integrity check used from legacy serial links to memory systems. Even parity’s definition is central to building and reading parity generators/checkers and debugging communication issues. Given Data / Assumptions: Single parity bit protects a data field. Even-parity scheme is specified. No multi-bit ECC is implied—just parity. Concept / Approach: The parity bit is set such that the total number of 1s in the code word (data + parity) is even. This permits detection of any odd number of bit errors (most notably single-bit flips). The definition is independent of line coding, voltage levels, or framing formats. Step-by-Step Solution: Count ones in the data field.If count is odd → parity bit = 1 to make the total even.If count is even → parity bit = 0 to keep the total even.Therefore, the given statement reflects the standard definition. Verification / Alternative check: Example: data 11001010 has four ones (even) → parity 0; data 11001011 has five ones (odd) → parity 1. Why Other Options Are Wrong: Incorrect: Opposes the textbook definition.True only for 8N1: Parity definition does not depend on UART framing style.Depends on voltage: Logic levels do not affect parity math. Common Pitfalls: Assuming parity corrects errors (it detects many, not all); mixing parity with checksums/CRCs. Final Answer: Correct

Question 17

Control structures in hardware description and firmware: “The CASE control structure is used when a single selector expression can take on a list of discrete values.” Evaluate this statement.

Accepted Answer

Introduction / Context: Both HDLs (e.g., VHDL, Verilog) and software languages use structured decision statements. Choosing between IF/ELSIF and CASE impacts readability and, in hardware, synthesizability and implementation efficiency (e.g., mux trees, decoders). Given Data / Assumptions: One selector expression is compared against multiple possible literal values or ranges. Branches are mutually exclusive and intended to cover all or most cases. CASE maps naturally to multiplexing/decoding hardware. Concept / Approach: Use CASE when switching on one variable with enumerated options (e.g., opcode, state). IF/ELSIF is better for arbitrary Boolean conditions or prioritized checks. The statement correctly characterizes CASE usage. Step-by-Step Solution: Identify a single selector (e.g., state, opcode).List discrete choices in CASE branches.Provide a default/others branch to handle unspecified values. Verification / Alternative check: In synthesis, CASE often infers efficient multiplexers or ROM-like structures; IF/ELSIF chains may infer priority encoders. This aligns with the stated guidance. Why Other Options Are Wrong: Incorrect: Misrepresents the canonical use of CASE.Only true for synthesis: The construct is also valid and clear in simulation.Only valid in software: HDLs use CASE extensively. Common Pitfalls: Forgetting a default/others branch; overlapping conditions that belong in IF/ELSIF instead; using CASE with non-discrete conditions. Final Answer: Correct

Question 18

Boolean simplification (sum-of-products): Simplify the expression AB + A'B to its simplest form using Boolean algebra laws.

Accepted Answer

Introduction / Context: Simplifying Boolean expressions reduces gate count, power, and delay. The expression AB + A'B is a common pattern that can be minimized using standard identities. Recognizing these patterns is essential in manual algebra and when checking tool results. Given Data / Assumptions: Expression: F = AB + A'B (where A' denotes NOT A). Variables A and B are independent Boolean variables. Goal: obtain the simplest logically equivalent form. Concept / Approach: Use the Distributive and Absorption laws. Note that both product terms share B. Factor B, then apply the Complementarity law A + A' = 1. This often collapses the expression to a single literal or a simpler term. Step-by-Step Solution: Start with F = AB + A'B.Factor B: F = (A + A') * B.Use complementarity: A + A' = 1.Therefore F = 1 * B = B. Verification / Alternative check: Truth-table check: when B = 0, both AB and A'B are 0 → F = 0; when B = 1, either A or A' is 1 → AB + A'B = 1 → F = 1. This matches F = B for all A. Why Other Options Are Wrong: A + B: Overstates the function; when A=1, B=0 this yields 1, but original F=0.AB: Too restrictive; when A=0, B=1 original F=1 but AB=0.A'B: Only covers the A=0, B=1 case, not A=1, B=1 which also yields 1. Common Pitfalls: Forgetting to factor the common literal; misreading A'B as A + B; confusing A + A' (which equals 1) with A * A' (which equals 0). Final Answer: B

Question 19

Karnaugh map (K-map) purpose: Confirm whether a K-map provides a graphical approach to minimizing (simplifying) Boolean sum-of-products expressions.

Accepted Answer

Introduction / Context: Karnaugh maps are a visual technique for simplifying Boolean expressions by grouping adjacent minterms to eliminate variables. They are widely taught as a stepping stone to Quine–McCluskey and modern synthesis tools. Given Data / Assumptions: We focus on minimizing sum-of-products (SOP) forms via minterm grouping. Variables typically range from 2 to 4 (paper), but 5–6 are possible with care. Adjacency is defined on Gray-coded map layouts. Concept / Approach: Each 1 cell on a K-map represents a minterm. Grouping 1s in powers of 2 (1, 2, 4, 8, …) removes changing variables from the product term, yielding simpler SOP expressions. K-maps also support POS by grouping 0s, but the statement’s focus on SOP is correct and common. Step-by-Step Solution: Plot minterms (1s) of the function on the map.Group adjacent 1s in largest possible power-of-two rectangles (wrapping edges is allowed).For each group, form the simplified product term by retaining only variables that do not change within the group.Sum (OR) the product terms to obtain the minimized SOP expression. Verification / Alternative check: Compare to algebraic simplification or to a logic minimizer; results match for canonical SOP minimization. Why Other Options Are Wrong: Incorrect: K-maps are indeed graphical simplifiers.Only POS: K-maps work for both SOP (group 1s) and POS (group 0s).Only for exactly 3 variables: Common from 2 to 4 variables; extensions exist for more. Common Pitfalls: Missing wrap-around adjacencies; making many small groups instead of fewer large ones; mixing SOP and POS grouping rules. Final Answer: Correct

Question 20

Form identification (SOP vs. others): Determine whether the Boolean expression A'B + AB' is in sum-of-products (SOP) form. Justify your classification.

Accepted Answer

Introduction / Context: Being able to recognize canonical forms accelerates simplification and hardware mapping. SOP (sum-of-products) means an OR (sum) of one or more product terms, where each product term is an AND of literals (variables or their complements). Given Data / Assumptions: Expression: F = A'B + AB'. Literal is a variable or its complement (e.g., A or A'). Product term is a logical AND of literals; sum is a logical OR of product terms. Concept / Approach: Check each term: A'B is a product (A' AND B). AB' is also a product (A AND B'). The entire expression is the sum (OR) of these two products. Therefore it fits SOP. Step-by-Step Solution: Identify product terms: P1 = A'B; P2 = AB'.Identify the outer operator: OR, combining P1 and P2.Conclude: F = P1 + P2 is in SOP form. Verification / Alternative check: Attempt POS recognition: POS requires a product (AND) of sum terms like (A + B)(A' + B'); our expression does not match that template, confirming SOP classification. Why Other Options Are Wrong: Incorrect: The structure clearly matches SOP.It is POS: Incorrect operator ordering.Neither SOP nor POS: It is a standard SOP example (an XOR-like form). Common Pitfalls: Confusing SOP with POS; overlooking that literals can be complemented and still be part of valid product terms; assuming canonical form must include all variables in every term (not required for non-canonical SOP). Final Answer: Correct

Combinational Logic Circuits Questions