Question 1

FLEX10K architecture — outputs available from a Logic Element (LE) In Altera’s FLEX10K devices, a Logic Element (LE) can drive which two on-chip interconnect resources directly?

Accepted Answer

Introduction / Context: FLEX10K is a classic FPGA family in which each Logic Element (LE) resides inside a Logic Array Block (LAB). Understanding where LE outputs can be routed clarifies how local vs. global connectivity works in the device and why certain placements yield better timing. Given Data / Assumptions: An LE is the basic logic + register resource inside a LAB. FLEX10K devices provide both local interconnect (within the LAB) and long/fast interconnect across LABs (often called FastTrack interconnect). The question asks for the two routing destinations an LE output may drive. Concept / Approach: LE outputs can be fed to neighboring LEs in the same LAB through the local LAB interconnect for short, low-delay routes, or they can be driven onto the device-wide FastTrack interconnect to reach distant LABs and I/O blocks. This dual routing strategy supports both dense local logic and broader chip-level connectivity. Step-by-Step Solution: Identify LE → local LAB interconnect path.Identify LE → FastTrack (global) interconnect path.These are the two fundamental destinations for an LE output.Therefore, select “The LAB and the fast track.” Verification / Alternative check: FLEX10K handbooks depict LE outputs feeding LAB local interconnect and the FastTrack network. Why Other Options Are Wrong: “ON/OFF,” “Hi-Z/ON,” “Hi-Z/OFF” describe pin states, not routing resources. Common Pitfalls: Confusing I/O pin tri-state behavior with internal routing options. Final Answer: The LAB and the fast track

Question 2

FPGA LUT basics — typical inputs and truth-table size In many mainstream FPGAs, a single look-up table (LUT) historically accepts how many inputs, and therefore stores how many truth-table entries (possible input combinations)?

Accepted Answer

Introduction / Context: A look-up table (LUT) is the core combinational element in most FPGAs. It implements any Boolean function of k inputs by storing a truth table with 2^k entries and using the input vector as an address. Many classic FPGA families used 4-input LUTs, while newer devices often use 6-input or larger LUTs. Given Data / Assumptions: We refer to common, historical mainstream devices (e.g., early Xilinx/Altera families). Each LUT output is one bit; the LUT stores 2^k configuration bits. The question asks for typical k and corresponding number of entries. Concept / Approach: If a LUT has k inputs, it must hold 2^k bits to represent all input combinations. For k = 4, this is 2^4 = 16 entries. Thus a single 4-input LUT stores 16 configuration bits that define its output for every possible 4-bit input pattern. Step-by-Step Solution: Recognize k-input LUT → 2^k truth-table entries.Plug in k = 4 → 2^4 = 16.Therefore, the pair is 4 inputs, 16 entries.Select option “4,16.” Verification / Alternative check: Older Spartan/Cyclone families feature 4-input LUTs (16-bit truth tables); modern 6-input LUTs store 64 entries, but the question targets the “most” common historical baseline. Why Other Options Are Wrong: 8,16: A LUT with 8 inputs would require 256 entries, not 16. 4,12 and 6,12: 12 is not a power of two; a proper LUT table size must be 2^k. Common Pitfalls: Assuming “outputs” means output pins; here it refers to truth-table entries stored in the LUT memory. Final Answer: 4,16

Question 3

From SPLD to larger architectures — adding an OR plane enables what device class? By augmenting a simple programmable logic device (SPLD) structure with an OR plane so that both AND and OR arrays are available, you create the foundation for which de…

Accepted Answer

Introduction / Context: SPLDs include device types like PALs and PLAs that implement sum-of-products logic. The key structural difference is whether the AND and OR arrays are programmable or fixed. Understanding this difference helps you map Boolean expressions efficiently to hardware. Given Data / Assumptions: We begin with a simple PLD structure. We add an OR plane to complement the AND plane. The question asks which device class this enables. Concept / Approach: A PAL typically has a programmable AND plane and a fixed OR plane; a PLA has both programmable AND and programmable OR planes. Therefore, when you explicitly add an OR plane as a programmable resource (not just fixed) to the basic structure, you are describing a PLA. A CPLD is essentially an array of multiple SPLD-like macrocells with routing; EEPROM is a memory technology, not a logic architecture class. Step-by-Step Solution: Identify PAL vs. PLA distinction (fixed vs. programmable OR plane).Adding a programmable OR array → matches PLA characteristics.Therefore, the resulting foundation is a PLA.Select option “PLA.” Verification / Alternative check: Textbooks show PAL: programmable AND, fixed OR; PLA: programmable AND and OR. CPLD aggregates many macrocells but is a different level of integration. Why Other Options Are Wrong: PAL: would not require adding a programmable OR plane, since its OR plane is fixed. CPLD: higher-level structure built from multiple SPLD-like blocks. EEPROM: storage technology, not a logic architecture. Common Pitfalls: Assuming PAL and PLA are interchangeable; the OR-plane programmability is the key differentiator. Final Answer: PLA

Question 4

Device identification — what is the EPM7128S? Identify the correct description of the part number “EPM7128S” commonly encountered in digital logic labs and CPLD development kits.

Accepted Answer

Introduction / Context: Part-number literacy is crucial when selecting programmable logic for a project or when reading reference designs. The EPM7128S appears in many educational boards and older industrial designs and belongs to a well-known CPLD family from Altera (now Intel PSG). Given Data / Assumptions: The identifier begins with “EPM,” which typically denotes Altera MAX-series CPLDs. “7128” suggests approximately 128 macrocells or a comparable density class within the family. “S” denotes the MAX7000S variant with in-system programmability improvements and other features. Concept / Approach: Altera’s MAX7000/7000S families are non-volatile CPLDs popular for deterministic timing, instant-on behavior, and ease of use. The EPM7128S sits squarely in this family and is recognized by toolchains such as MAX+Plus II and Quartus for classic flows. It is not a development board (UP2) or a generic educational SoC; it is the CPLD device itself. Step-by-Step Solution: Match “EPM” prefix to Altera MAX CPLD naming.Recognize “7128S” as the specific MAX7000S density/feature variant.Identify the device correctly as a MAX7000S CPLD.Exclude non-device answers (boards/kits). Verification / Alternative check: Legacy datasheets and lab manuals list EPM7128S as a MAX7000S family CPLD used on training boards. Why Other Options Are Wrong: UP2 is a development board that may include programmable logic, not the CPLD part name itself. DeVry eSOC / BSR PL DT-2 are not standard part-number identifications for this device. Common Pitfalls: Confusing a board SKU with the actual programmable logic device part number on the board. Final Answer: An Altera MAX7000S CPLD

Question 5

History of Programmable Logic — When did the first PLD (Programmable Logic Device) appear? Choose the most accurate time span based on industry milestones such as early PLAs (e.g., Intel 82S100 in the mid-1970s) and the first PAL families introduced…

Accepted Answer

Introduction / Context: The question tests basic historical awareness of programmable logic devices (PLDs). Understanding the timeline helps learners appreciate why PLDs, PALs, CPLDs, and FPGAs became dominant in digital design, replacing large amounts of fixed 7400-series logic with configurable alternatives. Given Data / Assumptions: The earliest commercially recognized PLD/PLA devices emerged in the 1970s. PAL families followed shortly thereafter and catalyzed widespread adoption. Today's date is long after those introductions, so multiple decades have elapsed. Concept / Approach: We map well-known product introductions to decade markers. If foundational devices appeared in the 1970s, then relative to modern dates the elapsed time exceeds 40 years. Even conservative estimates (late 1970s or early 1980s) still cross the 40-year threshold by the mid-2020s for the earliest parts. Step-by-Step Solution: Identify earliest PLD era: mid-1970s for early PLAs and late-1970s for PAL families.Compute elapsed time: from 1975–1979 to the present exceeds 40 years.Compare to choices: 10, 20, 30 years are all less than the historical span.Therefore, select “More than 40 years ago.” Verification / Alternative check: Standard histories of digital logic show PLD roots in the 1970s, predating CPLDs (late 1980s) and FPGAs (mid/late 1980s). Thus, the >40-year answer is consistent with multiple independent references and industry retrospectives. Why Other Options Are Wrong: More than 10 or 20 years: Far too recent; underestimates the technology's age. More than 30 years: Still less than the earliest introductions in the 1970s relative to today. Common Pitfalls: Confusing the first mass-market FPGAs (1980s) with the earlier PLD/PLA inventions; mixing up “first PLD” vs. “first FPGA.” Final Answer: More than 40 years ago

Question 6

Digital System Categories — Identify the major classes Digital design solutions can be grouped into several major categories. Which of the following are recognized categories used in industry and education?

Accepted Answer

Introduction / Context: Digital systems span a spectrum from fixed small-scale logic to highly integrated custom silicon. Recognizing the major categories helps engineers choose the right platform based on cost, performance, power, and time-to-market constraints. Given Data / Assumptions: Standard logic devices include SSI/MSI 7400/4000-series gates, counters, decoders, and simple glue logic. ASICs (Application-Specific Integrated Circuits) implement custom logic at the chip level for performance and power efficiency. Microprocessor/DSP devices are programmable compute engines controlled by software or firmware. Concept / Approach: Each listed option represents a widely accepted category. While there are additional classes (e.g., PLDs, CPLDs, FPGAs, SoCs), the options given already encompass three distinct and commonly taught categories. Therefore, the inclusive answer is “All of the above.” Step-by-Step Solution: Evaluate “Standard logic devices”: foundational building blocks → valid category.Evaluate “ASICs”: custom silicon pathway → valid category.Evaluate “Microprocessor/DSP devices”: programmable compute category → valid category.Since all are valid categories, choose “All of the above.” Verification / Alternative check: Introductory digital design textbooks and curricula list these categories alongside PLDs/FPGAs as common solution families, confirming their status as major categories. Why Other Options Are Wrong: Any single category alone omits the breadth of digital implementation approaches. Common Pitfalls: Assuming a mutually exclusive taxonomy; in practice systems combine categories (e.g., a microprocessor with standard-logic glue and ASIC peripherals). Final Answer: All of the above

Question 7

Sequential Logic — Another commonly used name In the context of digital circuits, what is another widely used description for circuitry referred to as “sequential logic”?

Accepted Answer

Introduction / Context: Digital logic is divided into combinational and sequential categories. Sequential logic stores state and reacts to both current inputs and past history. Understanding alternative phrasing helps connect textbook terminology with practical design discussions. Given Data / Assumptions: Sequential logic inherently uses storage elements (flip-flops, latches, memory). It relies on clock or timing events to update stored state. Combinational logic, by contrast, has no memory of past inputs. Concept / Approach: Because sequential circuits require flip-flops or latches to store state, they are often colloquially summarized as “flip-flop based memory circuitry.” This conveys the essential property: the presence of state (memory) updated by timing events. Step-by-Step Solution: Identify key trait of sequential logic: dependence on stored state.Recognize implementation: flip-flops/latches form the memory core.Map phrasing: “flip-flop memory circuitry” best matches sequential logic.Exclude unrelated terms: inverter (purely combinational), generic block names. Verification / Alternative check: State machines (Mealy/Moore) and pipelines are built from flip-flops plus combinational logic; documentation frequently refers to “sequential (flip-flop) logic.” Why Other Options Are Wrong: logic macrocell / logic array: Implementation terms that can include either combinational or sequential features; not a synonym for sequential per se. inverter: A single combinational gate with no memory. Common Pitfalls: Confusing storage with just propagation delay; memory requires explicit state elements (flip-flops/latches), not gate delay. Final Answer: flip-flop memory circuitry

Question 8

FPGAs — Programmable technologies used internally Modern FPGA families can be implemented with different configuration technologies. Which of the following are used across various vendors and generations?

Accepted Answer

Introduction / Context: Field-Programmable Gate Arrays (FPGAs) store configuration data that defines logic, routing, and I/O behavior. Vendors have adopted multiple nonvolatile and volatile technologies to hold this configuration, each with trade-offs in reprogrammability, power, security, and radiation tolerance. Given Data / Assumptions: SRAM-based FPGAs use external or on-chip memory to load bitstreams at power-up; they are fully reprogrammable. FLASH-based FPGAs retain configuration without external memory and allow many reprogram cycles. Antifuse FPGAs are one-time programmable with very robust, permanent connections. Concept / Approach: Across the industry, all three technologies have been used. Therefore, a correct high-level answer must include them collectively, not a single technology. Selecting “All of the above” accurately reflects the diversity of implementation technologies. Step-by-Step Solution: Evaluate SRAM: dominant for high-end, reconfigurable parts.Evaluate FLASH: used in nonvolatile, low-power families.Evaluate Antifuse: used where one-time programmability and radiation hardness are desirable.Conclusion: all listed technologies are used in FPGAs. Verification / Alternative check: Vendor literature shows SRAM (volatile), FLASH (nonvolatile), and Antifuse (OTP) product lines, confirming the breadth of approaches. Why Other Options Are Wrong: Choosing only one technology ignores substantial segments of the FPGA market. Common Pitfalls: Assuming only SRAM exists because it dominates high-end devices; many embedded FPGAs are FLASH-based, and Antifuse remains relevant in niche applications. Final Answer: All of the above

Question 9

OTP Devices — What does “OTP” stand for in programmable logic/memory? Select the correct expansion that matches how the term is used in datasheets and device programming contexts.

Accepted Answer

Introduction / Context: OTP appears in memory and programmable logic datasheets to indicate devices that can be programmed exactly once. This concept applies to antifuse FPGAs, certain PROMs, security fuses, and microcontroller configuration fuses, where permanence is a feature, not a limitation. Given Data / Assumptions: The term is used in the electronics domain, not optics or imaging. Programming actions are irreversible by design. OTP parts are often chosen for security, reliability, or certification reasons. Concept / Approach: Decode the acronym in the correct domain. In electronics, OTP unambiguously means “One-Time Programmable,” distinguishing it from reprogrammable FLASH, EEPROM, or SRAM-configured devices. Step-by-Step Solution: Identify domain: programmable logic/memory.Match acronym: OTP → One-Time Programmable.Eliminate distractors unrelated to electronics programming.Select “One-time programmable.” Verification / Alternative check: Device datasheets and programming manuals universally define OTP as one-time programmable, often citing antifuse mechanisms or PROM structures. Why Other Options Are Wrong: Other expansions are nonsensical in this technical context. Common Pitfalls: Assuming OTP implies limited value; in many applications, permanence is essential for tamper-resistance and certified behavior. Final Answer: One-time programmable

Question 10

PLD Taxonomy — Which of the following is NOT a recognized PLD class? Pick the option that does not correspond to a standard programmable logic device family.

Accepted Answer

Introduction / Context: Programmable logic device families are commonly grouped into SPLD (simple PLD), CPLD (complex PLD), and FPGA (field-programmable gate array). Knowing the taxonomy helps navigate datasheets and toolflows across vendors. Given Data / Assumptions: SPLD includes PAL/GAL/PLA-style devices. CPLD aggregates multiple macrocells/blocks with predictable timing. FPGA employs fine-grained LUTs, routing, and often embedded IP. Concept / Approach: Check each term against standard literature. SPLD, CPLD, and FPGA are canonical. “HPLD” is not a standard family acronym in mainstream usage, so it is the outlier. Step-by-Step Solution: Validate SPLD: recognized term.Validate CPLD: recognized term.Validate FPGA: recognized term.Identify HPLD: not a standard class → correct choice. Verification / Alternative check: Vendor training material and textbooks consistently use SPLD/CPLD/FPGA; “HPLD” does not appear as a family category. Why Other Options Are Wrong: SPLD, CPLD, FPGA: all legitimate PLD classes. Common Pitfalls: Assuming any acronym ending in “PLD” is a formal class; stick to widely accepted terms. Final Answer: HPLD

Question 11

Cascade Chains in Programmable Logic — What are they most closely associated with? Consider how designers build larger functions: cascade chains connect resources to create wider logic. They are closely associated with ________.

Accepted Answer

Introduction / Context: Cascade chains allow adjacent logic elements or macrocells to combine their outputs or product terms, creating wider functions than a single cell supports. They are a key mechanism for scaling sum-of-products (SOP) logic and for building adders, comparators, and decoders efficiently inside PLDs and FPGAs. Given Data / Assumptions: CLBs (Configurable Logic Blocks) or macrocells can forward signals along dedicated cascade paths. SOP implementations often need more product terms than one cell provides. Logic expansion is the design goal when simple cells are insufficient in isolation. Concept / Approach: Because cascade chains directly enable expansion of SOP terms and connect neighboring logic elements inside CLBs/macrocells, they are associated with all three listed concepts. The unifying idea is scaling capability within the fabric to implement wider functions without routing through general interconnect for every intermediate node. Step-by-Step Solution: Relate to CLBs: cascades are built into CLB/macrocells to share terms.Relate to SOP: cascades add product terms for larger SOP equations.Relate to logic expansion: cascades are the mechanism for expansion.Thus, “all of the above” best captures the association. Verification / Alternative check: Architecture guides for CPLDs/FPGAs document dedicated cascade lines used specifically for expanded logic or carry-like structures. Why Other Options Are Wrong: Picking only one element ignores the broader role of cascades across blocks, SOP equations, and general expansion. Common Pitfalls: Confusing carry chains (arithmetic focus) with cascade chains (general logic/SOP focus); they are related but distinct features in many architectures. Final Answer: all of the above

Question 12

PAL Device Fundamentals — Pin/function makeup of a PAL16L8 Considering standard 20-pin PAL16L8 devices, which pin/function mix is correct for inputs and outputs?

Accepted Answer

Introduction / Context: PAL (Programmable Array Logic) devices offered fixed OR planes with programmable AND arrays and configurable I/O macrocells. The PAL16L8 is a classic part number where “16” relates to the available product-term matrix width and “8” denotes eight outputs (often with active-LOW capability), making it a popular SPLD for glue logic. Given Data / Assumptions: Package: typically 20 pins (VCC and GND consume two pins). Eight output macrocells are present (the “8”). Remaining user pins are generally available as inputs. Concept / Approach: Subtract supply pins from the total, then account for eight output macrocells. The standard allocation yields ten input pins and eight output pins, with device-specific options for tri-state control or OE. Therefore, “10 inputs and 8 outputs” matches common PAL16L8 datasheets. Step-by-Step Solution: Total pins ≈ 20 → minus VCC and GND → 18 user pins.Eight are outputs (macrocell outputs).The remaining user pins serve as inputs (~10 inputs).Hence, PAL16L8 configuration: 10 inputs, 8 outputs. Verification / Alternative check: Legacy PAL/GAL datasheets list PAL16L8 as having 8 outputs and approximately 10 inputs, corroborating the standard understanding. Why Other Options Are Wrong: 8/8: Understates available inputs. 16/16 or 16/8: Do not match the pin budget or the “16L8” part family behavior. Common Pitfalls: Interpreting “16” as the number of inputs; instead it aligns with internal product-term matrix resources rather than literal user I/O counts. Final Answer: 10 inputs and 8 outputs.

Question 13

PLA vs. PAL — Key architectural difference Choose the correct statement comparing the programmability of the AND/OR planes in PLAs and PALs.

Accepted Answer

Introduction / Context: Both PLAs (Programmable Logic Arrays) and PALs (Programmable Array Logic) implement sum-of-products functions. Their principal architectural difference lies in which logic planes are programmable, a distinction that influences flexibility, density, and performance. Given Data / Assumptions: PLAs: both AND and OR arrays are programmable (max flexibility). PALs: programmable AND array feeding a fixed OR array (faster, simpler). Both implement logic using product terms summed (ORed) into outputs. Concept / Approach: Compare the programmability of planes directly. If both planes are programmable, that is a PLA. If only the AND plane is programmable, with a fixed OR structure, that is a PAL. This standard textbook distinction resolves the question. Step-by-Step Solution: Identify PLA: AND plane programmable; OR plane programmable.Identify PAL: AND plane programmable; OR plane fixed.Map to answer choices → option stating PLA has both programmable and PAL has only AND programmable is correct.Reject alternative claims that reverse or conflate the two. Verification / Alternative check: Datasheets and academic references consistently describe PLAs with full two-plane programmability and PALs with a single programmable plane. Why Other Options Are Wrong: Options B, C, D contradict accepted architectural definitions or make unfounded generalizations. Common Pitfalls: Assuming more programmability always equals better performance; PALs traded flexibility for speed and simplicity in many use cases. Final Answer: The PLA has a programmable OR plane and a programmable AND plane, while the PAL only has a programmable AND plane.

Question 14

Why PLDs Displaced Many Fixed-Function ICs — Key advantages What explains the broad market adoption of PLDs relative to piles of fixed 74xx logic and discrete glue ICs?

Accepted Answer

Introduction / Context: Programmable Logic Devices (PLDs), including SPLDs, CPLDs, and FPGAs, became popular because they consolidate functionality, accelerate design cycles, and reduce bill-of-materials. Understanding these benefits clarifies why programmable solutions displaced many fixed-function ICs in modern designs. Given Data / Assumptions: A single PLD can replace numerous SSI/MSI gates, counters, decoders, and glue logic. When considering total system cost (components, PCB area, assembly), PLDs can be cheaper. Lower quiescent power and reduced I/O toggling across many chips can decrease overall power. Concept / Approach: Evaluate each proposed advantage at the system level. While a PLD may be more expensive than one small IC, it often replaces many, shrinking the PCB, reducing routing complexity, and lowering inventory. Power savings can result from fewer I/O drivers and shorter interconnects, especially in CPLDs/modern FPGAs with low-power modes. Step-by-Step Solution: Function consolidation → fewer packages, simpler routing.Cost comparison → total BOM + assembly + engineering time can favor PLDs.Power analysis → fewer chip-to-chip transitions and modern low-power silicon reduce consumption.Thus, all listed advantages are valid in many real designs. Verification / Alternative check: Case studies and app notes show PLD-based designs meeting cost, power, and schedule goals more effectively than equivalent boards stuffed with numerous SSI/MSI devices. Why Other Options Are Wrong: Picking only a single benefit ignores the multi-dimensional advantages driving PLD adoption. Common Pitfalls: Comparing a PLD to just one small IC on unit price without considering the full system trade space (board area, time-to-market, reprogrammability). Final Answer: All of the above

Question 15

GAL (Generic Array Logic) design — source of flexibility In programmable logic devices, what specific architectural feature gives a GAL its notable flexibility for implementing either combinational or registered functions, polarity control, and tri-…

Accepted Answer

Introduction / Context: Generic Array Logic (GAL) devices evolved from earlier PAL parts to provide more design adaptability. While overall device speed and reprogrammable technology are beneficial, the core reason GALs are so versatile in practical designs lies in the output stage structure. This question targets your understanding of which internal block actually unlocks multiple implementation styles without changing the printed circuit board layout. Given Data / Assumptions: GALs contain a programmable AND array and a flexible output structure called an Output Logic Macrocell (OLMC). OLMCs can be configured for combinational or registered operation. OLMCs often support output polarity control and tri-state enable for bus interfacing. Device technology is typically EEPROM/Flash-like reprogrammability. Concept / Approach: The OLMC is a per-pin configurable block that sits between the internal product terms and the external I/O pin. By changing a few fuse/memory bits, you can select whether the macrocell uses a D-type flip-flop or bypasses it, whether the output is active-HIGH or active-LOW, and whether the pin drives, floats, or provides a feedback path into the array. This per-pin programmability is what converts one package into many possible logic functions. Step-by-Step Solution: Identify the architectural choices offered by a GAL: product terms feed OLMCs.Note that the OLMC can route product terms either to a DFF (registered) or directly to the pin (combinational).Recognize options like output polarity inversion and tri-state control within the OLMC.Conclude that this block, not merely speed or array size, enables the broad flexibility. Verification / Alternative check: Compare different pin functions (input, output, bidirectional) achievable via OLMC settings without changing board wiring. Datasheets show configuration tables where a single pin can serve multiple roles by programming the macrocell options. Why Other Options Are Wrong: Its speed: faster parts are helpful but do not inherently add functional flexibility. Its reprogrammable EPROM: reprogramming helps iterate designs, yet the versatile behavior comes specifically from the OLMC configuration choices. Its large logic arrays: more terms help capacity, not flexibility per pin. Common Pitfalls: Confusing “reprogrammable” with “reconfigurable per output.” The latter is delivered by the OLMC, which determines registered vs combinational modes, polarity, and tri-state features. Final Answer: Its programmable OLMCs

Question 16

Altera FLEX10K architecture — replacement for AND/OR arrays In the Altera (Intel) FLEX10K family of PLDs/CPLDs/FPGAs, what logic element is used in place of traditional sum-of-products AND and OR arrays?

Accepted Answer

Introduction / Context: Classic PAL/GAL devices implement logic as a programmable AND array feeding a fixed OR array (sum-of-products). More advanced programmable logic families migrated to look-up tables (LUTs), which store truth tables in small RAM-like structures. This question asks you to identify the core logic primitive used by Altera’s FLEX10K architecture instead of fixed AND/OR planes. Given Data / Assumptions: The device family uses fine-grained logic elements grouped into larger blocks. LUTs are typically implemented with SRAM cells to realize arbitrary Boolean functions of a small number of inputs. Modern FPGAs favor LUTs over hard-wired sum-of-products arrays. Concept / Approach: A k-input LUT directly encodes 2^k output values, enabling the device to implement any Boolean function of up to k variables by loading the appropriate configuration bits. This replaces the need for dedicated AND/OR matrices and allows flexible routing and packing of logic into logic array blocks within the fabric. Step-by-Step Solution: Recall FLEX10K belongs to FPGA/CPLD-like families that use LUT-based logic elements.Recognize LUTs implement functions by storing truth tables in configuration memory.Therefore, the correct answer is LUTs rather than AND/OR arrays. Verification / Alternative check: Vendor literature and architecture overviews consistently describe logic elements built around LUTs with optional flip-flops, carry chains, and routing resources. Why Other Options Are Wrong: “Nothing, it uses AND/OR arrays” contradicts standard FPGA architecture practice. “SRAM-based memory” is a technology detail used to implement LUTs but is not the logic primitive itself. “HPLD architecture” is not a standard logic primitive and does not identify the function element. Common Pitfalls: Confusing implementation technology (SRAM) with the logical abstraction (LUT). The LUT is the building block; SRAM stores its content. Final Answer: Look-up tables

Question 17

Identifying the PAL structure A device that consists of a programmable array of AND gates feeding a fixed array of OR gates, and that is usually one-time programmable (OTP), is called a:

Accepted Answer

Introduction / Context: Programmable logic devices come in many architectural flavors. Two historically important types are PALs and GALs. PALs generally provide a programmable AND plane and a fixed OR plane, while GALs add reprogrammable technology and versatile output macrocells. Understanding the architectural hallmark of a PAL helps you recognize its capabilities and limitations. Given Data / Assumptions: Structure: programmable AND array, fixed OR array. Programming model: typically one-time programmable (fuse/OTP). Target: choose the device class that best matches the structure and OTP behavior. Concept / Approach: The defining characteristic of a PAL (Programmable Array Logic) device is exactly this sum-of-products organization with a programmable AND matrix and fixed OR summation. Many PALs were OTP, distinguishing them from later GALs that used erasable technologies (e.g., EEPROM) and offered per-pin OLMC flexibility. Step-by-Step Solution: Match the described architecture to known device types.PAL fits “programmable AND + fixed OR” and “often OTP.”Therefore, select PAL. Verification / Alternative check: Historical datasheets and textbooks present classic PAL block diagrams showing an AND matrix with fixed OR gates driving outputs, sometimes with simple output enable/inversion controls. Why Other Options Are Wrong: GAL: similar purpose but reprogrammable with more flexible OLMCs. CPLD: multi-macrocell blocks with wider interconnect; not necessarily fixed OR planes as in classic PALs. SPLD: a generic category that includes PAL and GAL; not specific enough to match the exact description. Common Pitfalls: Confusing the general SPLD category with a specific architecture. Here the exact structure and OTP cue point to PAL. Final Answer: PAL

Question 18

Decoding the SPLD part number “22V10” For an SPLD labeled 22V10, what does this designation indicate about the device’s available inputs and outputs (independent of supply voltage)?

Accepted Answer

Introduction / Context: Manufacturers use shorthand part numbers to summarize capabilities. In many simple PLD families, the designation “22V10” conveys I/O resources and macrocell counts rather than supply voltage requirements. Correctly interpreting these labels is critical when sizing a device for a design (number of product terms, I/O count, and macrocell availability). Given Data / Assumptions: Naming convention: the first number indicates the count of inputs to the product-term array. The last number indicates the number of macrocells/outputs available. The letter “V” generally indicates variable or configurable output structures, not voltage rating. Concept / Approach: Under the common convention, “22V10” signifies 22 input lines feeding the programmable array and 10 output macrocells that can be configured as registered or combinational. It does not imply a 22 V or 10 V supply requirement. This understanding helps engineers select the right SPLD without misinterpreting power specifications. Step-by-Step Solution: Read “22” as number of inputs into the AND array.Read “10” as the number of OLMCs (outputs).Recognize that “V” denotes variable output modes in many families.Conclude: 22 inputs and 10 outputs. Verification / Alternative check: Cross-reference with typical GAL22V10 pinouts and block diagrams: they show ten macrocells and a set of shared input pins summed to approximately 22 signals into the matrix. Why Other Options Are Wrong: Options implying “requires 22 V or 10 V” misread the nomenclature; modern SPLDs use standard logic supplies, not 22 V. Reversing inputs/outputs contradicts standard usage. Common Pitfalls: Assuming the digits specify supply voltages; they do not. Always check the datasheet for actual Vcc and I/O electrical limits. Final Answer: 22 inputs and 10 outputs

Question 19

Inside an OLMC — FMUX destination Within an Output Logic Macrocell (OLMC) of a PAL/GAL-class device, the FMUX (feedback/data multiplexer) signal is routed to which internal element?

Accepted Answer

Introduction / Context: OLMCs (Output Logic Macrocells) provide per-pin configurability, including choices for combinational vs registered outputs, polarity inversion, tri-state control, and feedback. Understanding the internal multiplexers clarifies signal flow from the product-term matrix to the pin and back into the device for further logic. Given Data / Assumptions: The FMUX selects among product-term sources or feedback options used to drive the storage element's data input. OLMCs typically include a D-type flip-flop that can be inserted or bypassed. An OMUX usually selects what ultimately drives the pin (registered vs combinational path). Concept / Approach: The FMUX (feedback/data multiplexer) chooses the signal that feeds the D input of the macrocell's flip-flop. In contrast, the OMUX (output multiplexer) selects whether the pin sees the registered output or a direct combinational product-term sum. Recognizing these roles avoids confusion when reading configuration diagrams. Step-by-Step Solution: Identify FMUX as pre-register selection element.Trace its destination: the D input of the macrocell flip-flop.Contrast with OMUX, which selects the output drive source.Therefore, FMUX → D flip-flop. Verification / Alternative check: Consult common OLMC block drawings: the data path shows product terms entering an FMUX, then the DFF, then through OMUX to the I/O pin, with optional feedback paths into the matrix. Why Other Options Are Wrong: OMUX is post-register; it does not receive FMUX output directly. “Matrix” refers to the AND/OR array; FMUX does not feed back into the matrix directly. “PAL” is the device class, not an internal element. Common Pitfalls: Mixing up FMUX vs OMUX roles; assuming feedback always bypasses the register. Config bits determine registered or combinational operation and feedback source. Final Answer: D flip-flop

Question 20

LUT capacity — number of truth-table combinations In mainstream FPGA logic, a single 4-input LUT can realize how many distinct input combinations (i.e., truth-table entries) for one output?

Accepted Answer

Introduction / Context: Look-Up Tables (LUTs) are the fundamental logic primitives in many FPGA families. A k-input LUT implements any Boolean function of k variables by storing the function’s output values in 2^k memory cells and using the k inputs as an address into that small memory. Knowing 2^k is essential for estimating resource usage and fitting designs into a given device. Given Data / Assumptions: We consider a single 4-input LUT. Each unique input vector corresponds to one truth-table entry. One output bit per entry is stored in configuration memory. Concept / Approach: For k inputs, the number of possible input combinations equals 2^k. Therefore, a 4-input LUT has 2^4 = 16 addressable entries, each holding one output bit. By programming these 16 bits, the LUT can represent any mapping from 4 input bits to 1 output bit. Step-by-Step Solution: Compute combinations: for k inputs, combinations = 2^k.Substitute k = 4 → combinations = 2^4 = 16.Hence, a 4-input LUT stores 16 output bits, one per input address. Verification / Alternative check: Examine FPGA databooks: 4-input LUTs show a 16-bit configuration table; 6-input LUTs show 64 entries (2^6). Why Other Options Are Wrong: 4 and 8 underestimate the address space for 4 inputs. 32 corresponds to a 5-input LUT, not a 4-input LUT. Common Pitfalls: Confusing the number of inputs with the number of truth-table entries; forgetting that each additional input doubles the table size. Final Answer: 16

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