Question 1

Look-up table (LUT) concept in digital design Evaluate the statement: “A look-up table is simply a truth table with all possible output connections listed with their desired input response.” Is this statement accurate for LUTs used in FPGAs and logi…

Accepted Answer

Introduction / Context: Look-up tables (LUTs) are the fundamental combinational logic elements in most FPGAs. Conceptually, a LUT implements a truth table by storing the desired output for every combination of its input address lines. Understanding this makes it easier to map Boolean equations to FPGA resources and to visualize how synthesis tools realize logic. Given Data / Assumptions: A k-input LUT can represent any Boolean function of k variables. The LUT contains 2^k stored bits, each corresponding to one input combination. Inputs act as address lines; the stored bit at that address appears at the LUT output. Concept / Approach: Since each possible input vector is mapped to a predetermined output bit, a LUT is functionally equivalent to a truth table held in a small memory. Synthesis tools write these bits based on the designer’s Boolean description so that hardware performs the desired logic without enumerating explicit gate-level structures. Step-by-Step Explanation: Enumerate all input combinations (2^k addresses).Assign each combination an output value 0 or 1 as required.Store these values in a small memory array (the LUT).During operation, the current inputs select one stored bit that becomes the LUT output. Verification / Alternative check: Vendor documentation shows LUTs implemented as SRAM/flash bits feeding a multiplexer tree. This architecture is indistinguishable from a truth table abstraction: each address selects the predefined output bit. Why Other Options Are Wrong: “False” or conditions about synchronous logic/tri-state are irrelevant; LUTs are generic combinational elements. “Stores only state information” mischaracterizes LUTs; state storage is handled by flip-flops or block RAMs, not LUTs. Common Pitfalls: Confusing LUTs (combinational) with registers (sequential). Final Answer: True

Question 2

Electronics test methods — which uses external moving parts? Among common board-level test procedures, which method involves one or more external moving probes or parts during operation?

Accepted Answer

Introduction / Context: Manufacturing test strategies balance coverage, cost, and mechanical complexity. Classic fixtures such as bed-of-nails provide many simultaneous contacts but are mechanically static during the test. Newer strategies, including JTAG boundary scan, rely on on-chip instrumentation and require no moving parts. Flying-probe systems, however, physically move probes to contact nodes sequentially, offering flexibility without dedicated fixtures. Given Data / Assumptions: We are comparing fixture-based and probe-based board test methods. Boundary-scan (EXTEST) leverages on-chip registers to stimulate and observe pins. Flying-probe equipment positions probes dynamically over the PCB. Concept / Approach: The key discriminator is whether the test method requires mechanical motion during testing. Flying-probe machines move one or more needles under CNC control, contacting nets one at a time. Bed-of-nails fixtures are static pin arrays. Boundary scan and EXTEST operate electronically through the JTAG port without motion. Step-by-Step Reasoning: Identify mechanical movement: flying-probe heads traverse the board.Contrast to fixtures: bed-of-nails presses once and remains still during tests.JTAG-based methods manipulate scan chains electronically and need no moving parts. Verification / Alternative check: Review test equipment specs: flying-probe speeds are given in nodes-per-minute with axes travel specs, confirming mechanical movement. JTAG test descriptions reference TAP controllers, instruction registers, and boundary cells—no mechanical motion involved. Why Other Options Are Wrong: Bed-of-nails: static fixture. EXTEST and Boundary scan: electronic tests through JTAG. “In-circuit JTAG with static fixtures”: explicitly non-moving. Common Pitfalls: Assuming bed-of-nails “moves” because the press engages; the fixture does not move during measurement sequences. Final Answer: Flying probe

Question 3

PIA acronym in programmable logic In CPLD/FPGA architecture discussions, the acronym PIA most commonly stands for:

Accepted Answer

Introduction / Context: Programmable logic devices route signals through a fabric of configurable switch matrices. Terminology like “Programmable Interconnect Array (PIA)” is used to describe the reconfigurable network that connects macrocells, logic blocks, and I/O resources within devices such as CPLDs and some FPGAs. Given Data / Assumptions: Context is digital programmable logic architecture. We distinguish between logic resources (LUTs/macrocells) and routing resources (interconnect). Concept / Approach: The PIA is the configurable wiring matrix that allows arbitrary connections among logic elements and pins. By programming the PIA, synthesis and place-and-route tools create the intended signal topology without changing the silicon itself. This flexibility enables reuse of the same device across many designs. Step-by-Step Clarification: Identify the need: logic blocks must be connected to others and to I/O.Resource that provides connections: the interconnect fabric.Acronym “PIA” thus expands to “Programmable Interconnect Array.” Verification / Alternative check: Vendor literature for classic CPLDs describes a central “interconnect array” or “switch matrix,” commonly shortened to PIA, that ties macrocells and I/O blocks together via programmable fuses or EEPROM/flash configuration bits. Why Other Options Are Wrong: Programmable Interface/Input Array: not standard architecture terms. Post Integrated Array: not used in this context. Peripheral Interface Adapter: PIA also names a legacy I/O chip, but within programmable logic architecture, PIA stands for interconnect array. Common Pitfalls: Confusing architectural PIA with Motorola’s PIA peripheral; context determines meaning. Final Answer: Programmable Interconnect Array

Question 4

CPLD configuration memory — volatility characteristic A complex programmable logic device (CPLD) typically uses which type of on-chip configuration memory so that the user design is retained when power is removed?

Accepted Answer

Introduction / Context: CPLDs and FPGAs differ notably in how they store configuration. Classic CPLDs employ nonvolatile technologies (EEPROM/flash/antifuse) that retain user logic without external configuration memory, enabling instant-on behavior and simplified system design compared to many SRAM-based FPGAs that require bitstream loading on power-up. Given Data / Assumptions: CPLD families are commonly flash- or EEPROM-based. Nonvolatile storage retains configuration without power. Some modern FPGAs are SRAM-based and volatile (not the case for typical CPLDs). Concept / Approach: Because CPLDs target glue logic and deterministic startup, nonvolatile configuration is preferred. The device powers up directly into the user-defined behavior with minimal latency and no need for an external configuration ROM or processor to load a bitstream. Step-by-Step Reasoning: Identify device class: CPLD.Recall typical storage: EEPROM/flash/antifuse → nonvolatile.Conclude that the correct characteristic is nonvolatile storage. Verification / Alternative check: Datasheets for common CPLD families (e.g., Xilinx CoolRunner, Intel/Altera MAX) state nonvolatile configuration using flash/EEPROM cells, confirming persistence across power cycles. Why Other Options Are Wrong: volatile: describes SRAM-based architectures, more common in FPGAs. EPROM: a specific technology once used in PLDs; while nonvolatile, CPLDs typically use EEPROM/flash with electrical erase, not UV EPROM. “volitile EPROM”: misspelled and contradictory; EPROM is nonvolatile. battery-backed SRAM: not typical for CPLDs. Common Pitfalls: Assuming all programmable logic behaves like SRAM-based FPGAs; CPLDs are different. Final Answer: nonvolatile

Question 5

SPLD nomenclature — meaning of “16H8” An SPLD (e.g., PAL/GAL) listed as 16H8 most likely indicates which output polarity characteristic?

Accepted Answer

Introduction / Context: Older SPLD parts (PALs/GALs) often use letter codes to denote output behavior and resources. For instance, R, L, and H letters can indicate Registered outputs, active-Low outputs, or active-High outputs, respectively. Understanding these codes helps interpret datasheets and choose pin-compatible replacements. Given Data / Assumptions: Device code format “16H8”. “16” typically refers to available input terms; “8” refers to the number of outputs. Letter “H” indicates a polarity characteristic of the outputs. Concept / Approach: Historically, families such as PAL16L8 (L = active-Low outputs), PAL16H8 (H = active-High outputs), and PAL16R8 (R = registered outputs) follow a naming convention where the letter conveys output style. Therefore, “H” denotes active-High outputs for that device variant. Step-by-Step Reasoning: Decode numeric fields: 16 inputs, 8 outputs (typical interpretation).Interpret letter “H” per convention: High-true outputs.Conclude: 16H8 devices have active-HIGH outputs. Verification / Alternative check: Check part tables listing PAL16H8 vs PAL16L8. The latter explicitly states active-Low outputs, while the former specifies active-High, confirming the polarity implication of the letter code. Why Other Options Are Wrong: active-LOW outputs: would be “L” variant. variable-level / tristate-only: not standard SPLD naming implications. latches at the outputs: would be indicated by other letters or specific part numbers; “R” generally denotes registered outputs (flip-flops), not latches. Common Pitfalls: Assuming all PAL/GAL codes are identical across vendors; always confirm in the specific datasheet. Final Answer: active-HIGH outputs

Question 6

FPGA building blocks In field-programmable gate arrays (FPGAs), which section of embedded logic forms the fundamental programmable element used to implement combinational functions?

Accepted Answer

Introduction / Context: The core of modern FPGA architecture is a highly regular fabric composed of small, repeatable logic elements. Understanding what these elements are and how they map HDL code into hardware is essential for designers targeting efficient, portable implementations across device families. Given Data / Assumptions: The question concerns the fundamental combinational logic resource inside an FPGA. Focus is on general-purpose logic used to realize Boolean expressions. We distinguish between embedded hard blocks (such as DSP slices) and soft, programmable logic. Concept / Approach: A lookup table (LUT) is a small truth-table memory that outputs a value based on its input address bits. For example, a 4-input LUT implements any Boolean function of four variables by storing the appropriate 16-bit truth table. Synthesis tools decompose HDL expressions into networks of LUTs and registers, then pack these into configurable logic blocks (CLBs/ALMs/logic elements). While FPGAs also include embedded memories, PLLs, and DSP blocks for multiply-accumulate operations, the LUT remains the basic “universal gate” resource for combinational logic. Step-by-Step Solution: Identify the fundamental combinational element in the fabric: the LUT.Recognize that LUTs implement arbitrary truth tables by storing precomputed output values.A register (flip-flop) is typically colocated with each LUT to implement sequential logic efficiently.Conclude that among the choices, LUT is the correct name for the embedded logic section commonly found in all FPGAs. Verification / Alternative check: Review any vendor architecture overview (for example, Xilinx CLB/SLICE, Intel Logic Array Block). All describe LUT-based logic elements as the base combinational resource, confirming this answer across vendors and families. Why Other Options Are Wrong: core: Vague term; not a specific logic primitive. DSP: A specialized hard block for arithmetic acceleration, not the general-purpose element. PI: Not a standard FPGA primitive acronym in this context. Common Pitfalls: Confusing LUTs with block RAM (both store bits) and assuming DSP slices replace LUTs for all arithmetic; in reality, many arithmetic and control functions still synthesize to LUT networks. Final Answer: LUT

Question 7

FPGA/PLD tool flow In a typical programmable logic device workflow (synthesis → fitting/place-and-route → bitstream generation → …), what is the final step that actually configures the target device?

Accepted Answer

Introduction / Context: Designing for FPGAs or CPLDs involves multiple software steps before the design runs on silicon. Newcomers often confuse offline steps (simulation, synthesis, place-and-route) with the step that physically programs the device. Clarifying this order avoids costly lab time and misdiagnoses when a board appears unresponsive. Given Data / Assumptions: The standard flow includes simulation, synthesis, implementation (fitting/place-and-route), and bitstream generation. Programming cables (JTAG/USB-Blaster/Platform Cable) or configuration memories are used for final configuration. Terminology varies by vendor (programming, configuring, downloading), but the concept is the same. Concept / Approach: Synthesis translates HDL to a technology-mapped netlist. Implementation places and routes that netlist into the device resources. Bitstream generation produces a configuration file (for example, .bit, .sof, .pof). None of those steps alone configures the chip. The design only becomes active after the configuration image is transferred to the device (or to a companion configuration flash) via a download/programming step. Step-by-Step Solution: Verify functional intent using simulation (pre/post-implementation as needed).Synthesize HDL into a device-specific netlist.Place and route (fit) the design and generate a programming file (bitstream).Download/program the device with the bitstream to make the design run in hardware. Verification / Alternative check: In vendor tools (for example, Quartus, Vivado), the final action that changes board behavior is the “Program/Configure Device” step, confirming that downloading is the last step that actually applies the design. Why Other Options Are Wrong: compiling / synthesis: These are software steps that create a bitstream but do not load it onto the device. simulation: Verifies function but does not affect hardware configuration. Common Pitfalls: Assuming that a successful bitstream build automatically configures the device, or forgetting to select the correct cable/chain, which leaves the old design running. Final Answer: downloading

Question 8

FPGA configuration technology Most field-programmable gate arrays (FPGAs) store their configuration using ________ memory technology, which is ________. Choose the most accurate pairing.

Accepted Answer

Introduction / Context: FPGAs must load their configuration at power-up. The memory technology used determines whether the device is self-retaining (nonvolatile) or requires an external or internal configuration source each time it powers on. This has implications for boot time, security, and board architecture. Given Data / Assumptions: We are discussing mainstream SRAM-based FPGAs (for example, Intel/Altera, Xilinx families). Nonvolatile families (for example, Flash-based) exist but are not the majority. Volatile memory loses its contents when power is removed. Concept / Approach: Most high-performance FPGAs use static RAM (SRAM) cells to control routing switches and LUT contents. SRAM is volatile, so configuration vanishes at power-off. Therefore, a configuration image must be delivered at boot (via JTAG, a configuration flash, or a processor). Flash-based or antifuse FPGAs are nonvolatile but represent a different subset of the market and usually are not implied by the generic term in this question. Step-by-Step Solution: Identify common device families that use SRAM configuration cells.Recall that SRAM loses state without power; thus the FPGA needs a bitstream each boot.Map the pairings: SRAM ↔ volatile is the correct match.Conclude that “SRAM, volatile” is the most accurate general statement. Verification / Alternative check: Examine vendor datasheets: they state that configuration is loaded from external memory or via programming cable at power-up for SRAM-based devices. Why Other Options Are Wrong: DRAM, nonvolatile: DRAM is also volatile and requires refresh. SRAM, nonvolatile: Contradiction; SRAM is volatile. RAM, volatile: Too generic; does not specify the specific technology normally used (SRAM). Common Pitfalls: Assuming all FPGAs are nonvolatile; overlooking configuration security measures such as bitstream encryption used with volatile storage. Final Answer: SRAM, volatile

Question 9

Embedded functions in modern FPGAs Which of the following best represents an embedded (hardened) function available in devices such as the Stratix II FPGA family?

Accepted Answer

Introduction / Context: Beyond LUT-based general logic, modern FPGAs integrate hardened blocks to accelerate specific tasks. Recognizing these embedded resources helps designers map compute-intensive algorithms to efficient hardware and meet timing/power goals. Given Data / Assumptions: Stratix II-class devices include dedicated multipliers/accumulators and DSP slices. Generic AND/OR logic and sum-of-products (SOP) are realized in LUTs, not as separate hard blocks. “Embedded” refers to specialized silicon macros integrated alongside the fabric. Concept / Approach: Digital signal processing (DSP) blocks provide fast multipliers, adders, and pipeline registers optimized for high-throughput arithmetic (for example, FIR filters, FFTs). These are distinct from the soft logic fabric that implements AND/OR/SOP terms. Selecting the DSP block offloads heavy arithmetic from LUTs, achieving higher performance and lower resource usage. Step-by-Step Solution: Identify which options describe hardened blocks versus soft logic.DSP functionality matches known embedded slices in Stratix II devices.Confirm that AND/OR and SOP structures are implemented via LUTs rather than dedicated hard macros.Therefore, pick “Digital signal processing.” Verification / Alternative check: Vendor architecture guides list embedded multipliers/DSP blocks, block RAMs, PLLs, and serializers/deserializers, validating the choice. Why Other Options Are Wrong: AND-OR logic / Programmable SOP: These are synthesized into LUT fabric, not “embedded functions.” None of the above: Incorrect since DSP blocks are indeed embedded. Common Pitfalls: Assuming that common logic expressions imply special hardware support; while some families include carry chains, generic SOP is not an embedded block separate from the LUTs. Final Answer: Digital signal processing

Question 10

PAL behavior Programmable Array Logic (PAL) devices are primarily optimized to implement which canonical Boolean form in their fixed OR structure?

Accepted Answer

Introduction / Context: Classic PALs and GALs are foundational programmable logic devices used to realize control logic, decoders, and glue logic. Their internal structure shapes which Boolean form is most natural and resource-efficient to implement. Given Data / Assumptions: PALs typically have a programmable AND array and a fixed OR array (with optional output macrocells). The canonical “sum-of-products” (SOP) form maps efficiently through programmable product terms into the fixed OR gates. Alternate canonical forms (product-of-sums) can be transformed but may be less direct. Concept / Approach: In SOP, each product term (AND of literals) represents a minterm or implicant. PALs allow selecting input polarities and combining them through the programmable AND plane to create these terms. The fixed OR plane sums selected products to produce each output. Therefore, equations naturally expressed as SOP best exploit PAL topology and minimize resource consumption and timing complexity. Step-by-Step Solution: Express target functions in SOP form by deriving product terms from the truth table.Program the AND array to realize required products.Use the fixed OR array to sum products into outputs, optionally feeding macrocells for registered or combinational outputs.Verify with timing analysis that product-term fan-in meets device limits. Verification / Alternative check: Device datasheets show product-term limits per output and programming fuses in the AND plane, confirming the SOP-centric design. Why Other Options Are Wrong: SAP / SPD: Not standard Boolean forms. PLA: Refers to a device class (Programmable Logic Array), not a Boolean form; PLAs have both programmable AND and OR planes. Common Pitfalls: Attempting POS implementations directly in a PAL without first transforming to SOP may waste terms or exceed device limits. Final Answer: SOP

Question 11

PAL/GAL macrocell placement Within a traditional PAL or GAL architecture, where are the macrocells located relative to the programmable arrays?

Accepted Answer

Introduction / Context: Macrocells provide output-specific features such as optional output registers, tri-state control, polarity options, and feedback paths. Knowing where they sit in the signal path helps you understand timing and feedback routing when implementing counters, state machines, or wide decoders in PAL/GAL devices. Given Data / Assumptions: PAL/GAL devices have a programmable AND array feeding a fixed OR array. Outputs often pass through macrocells offering register/combination selection and feedback. Inputs feed the AND array independently. Concept / Approach: Signals flow from inputs → programmable AND → fixed OR → macrocell → output pin (with possible feedback from macrocell to the AND array). Thus, the macrocell belongs at the output side, where it can condition, register, or invert the signal and control I/O behaviors such as tri-stating on bus interfaces. Step-by-Step Solution: Trace signal path through AND/OR planes.Observe that the macrocell comes after OR combination to finalize output behavior.Use macrocell options (register enable, output enable) per design needs.Feed back from macrocell to AND plane if internal recursion or state is required. Verification / Alternative check: Typical PAL/GAL block diagrams show macrocells physically and logically adjacent to output pins, confirming placement at the output terminals. Why Other Options Are Wrong: after the programmable AND arrays: Incomplete; must include the OR array and specifically the output side. ahead of the programmable AND arrays / at input terminals: Opposite of the actual flow. Common Pitfalls: Misunderstanding feedback timing from macrocell outputs back into the AND plane, which affects setup/hold for registered implementations. Final Answer: at the output terminals

Question 12

Inside a simple PLD The internal content and programmability of a simple programmable logic device (PLD) are best described as which of the following?

Accepted Answer

Introduction / Context: Before large FPGAs, designers used simple PLDs—PALs, GALs, and small CPLDs—for glue logic and control. Knowing what is actually programmable inside these devices clarifies their capabilities and limitations versus gate arrays and modern FPGAs. Given Data / Assumptions: “Simple PLD” refers to classic PAL/GAL-style devices, not high-density FPGAs or complex CPLDs. Programming technology historically uses fuses, antifuses, EPROM/EEPROM, or flash to configure connections in the AND (and sometimes OR) plane. They do not literally contain thousands of discrete gates like a gate array. Concept / Approach: Simple PLDs implement logic by selectively connecting input signals (and their complements) to product-term lines through programmable links (fuses, floating gates, etc.). The resulting AND terms feed a fixed OR plane and macrocells. Hence, the essence of programmability lies in the array of programmable interconnect links, not a sea of individually addressable gates or complex sequential macros by default. Step-by-Step Solution: Identify the programmable resource: connection (fuse-link) arrays.Map logic equations (SOP) onto product terms via these links.Use macrocells to register or invert outputs as needed.Conclude that “fuse-link arrays” best describes the internal content of simple PLDs. Verification / Alternative check: Manufacturer block diagrams and programming algorithms (for example, JEDEC fuse maps) directly show arrays of programmable links. Why Other Options Are Wrong: thousands of gates / advanced sequential logic: Describe gate arrays or FPGAs, not simple PLDs. Combination of both: Overstates capabilities beyond “simple” PLDs. Common Pitfalls: Equating CPLDs/FPGAs with simple PALs and expecting large embedded sequential feature sets. Final Answer: fuse-link arrays

Question 13

Understanding FPLA structure A Field-Programmable Logic Array (FPLA) is best characterized as which of the following?

Accepted Answer

Introduction / Context: An FPLA is an early but important programmable logic architecture that predates large-scale FPGAs. Understanding its internal structure helps clarify differences between PLAs, PALs, and GALs, and why certain Boolean forms map efficiently to particular devices. Given Data / Assumptions: FPLAs are configured electrically (for example, fuses/antifuses) and do not store user data like RAM. They include programmable AND and programmable OR planes. They are used to implement logic functions, not as general-purpose memory. Concept / Approach: In a PLA, both the AND and OR arrays are programmable. The AND plane generates product terms from inputs and their complements, and the OR plane sums any subset of those products to create outputs. Because configuration determines connectivity rather than stored user data, an FPLA is considered a nonmemory programmable logic device (its programmability defines logic structure, not runtime data storage). Step-by-Step Solution: Recognize that FPLA ≈ PLA with field programmability.Confirm that the AND plane is programmable to form required product terms.Confirm that the OR plane is programmable to combine products into outputs.Note that it is not “memory” in the sense of RAM/ROM used for data storage. Verification / Alternative check: Textbook diagrams show both planes as programmable matrices with fusible links; device programming files specify which intersections are connected. Why Other Options Are Wrong: Single-plane answers (only AND or only OR) are incomplete. Calling it memory-focused would misrepresent the device’s purpose. Common Pitfalls: Confusing PLAs (programmable OR+AND) with PALs (programmable AND + fixed OR) and assuming identical resource limits. Final Answer: All of the above

Question 14

Package pin count (device family example) For the EPF10K70/EDF10K70 device family (a member of classic 10K-series programmable logic), which of the following standard package options matches a commonly available pin count?

Accepted Answer

Introduction / Context: Programmable logic devices are offered in multiple packages (PQFP, TQFP, BGA, etc.), each with different pin counts, pitch, and thermal characteristics. Recognizing a typical pin count for a given density device helps with footprint selection, I/O planning, and board-level integration during early design stages. Given Data / Assumptions: The device referenced belongs to the 10K-series family (for example, EPF10K70/EDF10K70), historically available in multiple package options. Common package choices for mid-density parts include ~208–256 pin QFP/TQFP or similar counts, with higher-end variants in larger BGAs. We select the pin count that aligns with a widely used, practical package for that class of device. Concept / Approach: Mid-range programmable logic from this family was frequently offered in packages around the 240-pin range for designs needing significant I/O while balancing cost and PCB complexity. While alternate packages may exist, choosing the commonly cited 240-pin option aligns with standard reference designs and evaluation boards from that era. Step-by-Step Solution: Identify that very low pin counts (for example, 70) are atypical for a 70k-gate-class device.Recognize that extremely high counts (for example, 532) were reserved for larger, later-generation BGAs.Select the mid-range, widely documented package option near 240 pins.Therefore, choose 240 as the correct answer for a common package configuration. Verification / Alternative check: Historical datasheets and board designs for 10K-series parts list multi-hundred-pin packages with 200–256 pins as prevalent; 240 aligns with those offerings. Why Other Options Are Wrong: 70 / 140: Too few pins for the I/O needs of this density. 532: Much higher than typical for this family and era, more aligned with very large BGAs in newer families. Common Pitfalls: Assuming a single, unique pin count per device; in reality, multiple packages may exist. Here we select a representative, commonly used option consistent with the series capabilities. Final Answer: 240

Question 15

Programmable logic devices (PLDs) — which device types can implement basic custom logic functions? In the context of digital design, identify which category of PLD can be used to program and realize simple combinational and/or sequential logic funct…

Accepted Answer

Introduction / Context: Programmable logic devices (PLDs) provide field-configurable hardware for implementing digital logic without fabricating a custom chip. This question checks whether you recognize that multiple PLD families—Programmable Logic Arrays (PLA), Programmable Array Logic (PAL), and Complex PLDs (CPLD)—can all implement basic logic functions such as decoders, state machines, and glue logic. Given Data / Assumptions: PLA devices have programmable AND and programmable OR arrays. PAL devices typically have a programmable AND array and a fixed OR array, with optional output polarity control. CPLDs combine many PAL/PLA-like macrocells with routing to realize larger designs. Concept / Approach: Any device that provides user-programmable product terms (AND terms) and a way to sum them (OR terms), with optional registers, can implement basic logic functions. PLAs and PALs are the classical building blocks for small to medium functions, whereas CPLDs scale these ideas into larger, more integrated packages. Therefore, all three can be used to implement simple logic safely and effectively. Step-by-Step Solution: Identify the required capability: user-programmable logic realization.PLA: programmable AND + programmable OR → supports arbitrary sum-of-products.PAL: programmable AND + fixed OR → widely used for basic logic and registered outputs.CPLD: aggregates many PAL/PLA-like macrocells → certainly capable of basic logic.Hence, all the above choices are valid. Verification / Alternative check: Vendor datasheets (e.g., classic PAL/GAL parts and CPLD families like MAX7000 or XC9500) explicitly show sum-of-products structures that implement the same fundamental logic forms taught in digital design courses. Why Other Options Are Wrong: PLA only: too narrow—PAL and CPLD also work. PAL only: ignores PLA and CPLD capabilities. CPLD only: ignores that smaller PLDs can do the same basics. Common Pitfalls: Assuming “CPLD” is needed for everything; for small tasks, a PLA/PAL (or GAL) is often simpler and cheaper. Final Answer: all the above

Question 16

ASIC acronym — expand the term used in custom silicon design In VLSI and digital system design, what does the acronym “ASIC” stand for?

Accepted Answer

Introduction / Context: Engineers often choose between general-purpose programmable logic (FPGAs/CPLDs) and custom silicon. The acronym “ASIC” is foundational terminology that identifies chips manufactured to implement a particular application, not a general-purpose reprogrammable fabric. Given Data / Assumptions: We are identifying the correct expansion of the acronym “ASIC.” Context: chip design and fabrication targeting a specific application’s requirements. Concept / Approach: An ASIC is fabricated for a single, well-defined task or product family. Unlike FPGAs, its logic function is fixed at manufacture time. The key phrase is “application specific,” indicating that the circuitry is tailored to a particular need, often optimizing area, performance, and power beyond what a generic device can offer. Step-by-Step Solution: Identify “A” as “application.”Recognize “S” as “specific.”“IC” stands for “integrated circuit.”Combine to get “application specific integrated circuit.” Verification / Alternative check: Standard textbooks and industry documentation universally define ASIC as “application specific integrated circuit.” Why Other Options Are Wrong: “advanced speed/standard/speedy” are not canonical expansions; they are misleading backronyms. Common Pitfalls: Confusing ASICs with ASSPs (application-specific standard products), which are pre-made chips for specific functions but sold to many customers. Final Answer: application specific integrated circuit.

Question 17

Vendor terminology in FPGAs — what does ALM stand for? In modern FPGA architecture (e.g., Intel/Altera devices), expand the acronym “ALM.”

Accepted Answer

Introduction / Context: FPGA vendors use specific names for their basic programmable logic units. Intel (formerly Altera) refers to its enhanced logic element as an ALM, which expands capability beyond earlier single 4-input LUT logic elements by offering adaptive partitioning and efficient mapping of diverse logic functions. Given Data / Assumptions: The question asks for the expansion of the acronym ALM in the context of FPGA devices. We assume the vendor is Altera/Intel, where ALM is standard terminology. Concept / Approach: An ALM (Adaptive Logic Module) typically contains resources that can implement multiple small LUTs or a single larger function, along with optional arithmetic mode support, carry chains, and registers. The term “adaptive” highlights its flexibility for mapping different logic structures efficiently. Step-by-Step Solution: Identify the vendor context (Altera/Intel) where ALM is defined.Recall that ALM enhances the basic LUT+FF concept with adaptive partitioning.Expand the acronym: Adaptive Logic Module.Confirm no other listed expansion matches standard literature. Verification / Alternative check: Vendor handbooks and device datasheets consistently use “Adaptive Logic Module” for ALM. Why Other Options Are Wrong: Array Logic Matrix / Arithmetic Logic Module sound plausible but are not the vendor-defined term. Asynchronous Local Modulator is unrelated to FPGA logic blocks. Common Pitfalls: Confusing “ALM” with generic “logic element (LE)”—an ALM is a more capable evolution of the LE concept. Final Answer: Adaptive Logic Module

Question 18

Product-term expansion in PLDs — which feature borrows unused product terms from nearby macrocells? Identify the PLD feature name that increases the number of product terms available to a macrocell by borrowing unused terms from adjacent macrocells.

Accepted Answer

Introduction / Context: In classic CPLD architectures (e.g., Altera MAX series), each macrocell has a limited number of product terms. Some designs require more product terms for a single output equation. Vendors provide “expander” mechanisms to borrow unused product terms from neighboring macrocells to meet this need. Given Data / Assumptions: Macrocells reside inside a logic array block (LAB). Certain expanders make additional product terms available to a target macrocell. We must identify which named feature performs this borrowing in parallel. Concept / Approach: “Parallel expanders” add extra product terms to an equation by feeding additional ANDed terms directly into the OR stage of the target macrocell. This effectively widens the sum-of-products without moving the function to a different macrocell. “Shared expanders” generally distribute signals to multiple macrocells rather than increase a single macrocell’s product-term budget. Step-by-Step Solution: Determine the need: more product terms for one output equation.Look for a mechanism that borrows from neighbors within the LAB.Select “Parallel expander,” which specifically adds terms in parallel to the target OR array.Eliminate “Shared expander” since it primarily distributes terms rather than simply add to one macrocell's count. Verification / Alternative check: MAX7000 family documentation describes both shared and parallel expanders, with “parallel” explicitly for borrowing product terms to expand an equation. Why Other Options Are Wrong: Shared expander: aids sharing, not strictly increasing one macrocell’s term budget. Series/slice expanders: not standard names for the described function. Common Pitfalls: Assuming “shared” means “more terms”; in practice, it is about distributing existing terms, not expanding a single equation’s width. Final Answer: Parallel expander

Question 19

Altera MAX+Plus II fitting — maximum borrowed product terms in one LAB In a MAX+Plus II flow for a MAX-series CPLD, how many product terms can the fitter borrow from adjacent macrocells within the same LAB to extend one macrocell's equation?

Accepted Answer

Introduction / Context: When targeting CPLDs such as the Altera MAX7000 family, synthesis and fitting tools (e.g., MAX+Plus II) can allocate additional product terms to a single macrocell by borrowing from its neighbors in the same logic array block (LAB). Knowing the typical borrowing limit helps designers estimate resource sufficiency before place-and-route. Given Data / Assumptions: Target device family is Altera MAX (MAX+Plus II era). Borrowing occurs only within the same LAB. The question asks for the maximum number of borrowed product terms. Concept / Approach: Each macrocell has a base number of product terms. With parallel expander connections and fitter optimizations, extra product terms may be sourced from adjacent macrocells. Practical limits exist to preserve routability and ensure timing closure. The commonly cited value in training materials is up to 10 additional product terms borrowed for one macrocell equation inside a LAB. Step-by-Step Solution: Identify CPLD resource: product terms per macrocell.Apply parallel expander concept to borrow neighbors’ terms.Recall MAX+Plus II typical borrowing limit: up to 10 terms.Therefore, select 10 as the answer. Verification / Alternative check: Historical Altera training slides and user guides for MAX7000 devices reference borrowing up to 10 product terms via expanders to a single macrocell. Why Other Options Are Wrong: 0: contradicts the purpose of expanders. 5: too conservative relative to documented capability. 20: exceeds common per-macrocell borrowing limits in a single LAB. Common Pitfalls: Confusing total product terms available in a LAB with the maximum that can be concentrated onto one macrocell via expanders. Final Answer: 10

Question 20

Reading PLD array diagrams — meaning of a “dot” at an array intersection On classic PLD schematic/array diagrams (AND-OR planes), what does a filled dot at the intersection of a line and a product/sum term signify?

Accepted Answer

Introduction / Context: PLD documentation often shows a grid: input signals (and sometimes their complements) run one way; product terms run the other. Small dots indicate whether a connection exists between a signal line and a product/sum term. Understanding this notation is essential when interpreting fuse maps or logic array diagrams. Given Data / Assumptions: The diagram is a PLD logic array (e.g., programmable AND plane). Dots indicate configuration at crosspoints. Programming sets or clears these connections. Concept / Approach: A “dot” marks a programmed connection at a crosspoint, meaning that the corresponding signal participates in the product term (or sum term, in a PLA). Erasing the dot means the connection is absent. In older fuse-link devices, blowing a fuse removes the connection; in EEPROM/Flash-based PLDs, a memory bit enables or disables it. Step-by-Step Solution: Identify the grid: signals vs. product/sum terms.Interpret a dot as an enabled crosspoint connection.Recognize that programming sets these dots; reprogramming changes them.Therefore, a dot indicates a programmable (enabled) connection. Verification / Alternative check: Device manuals show sample arrays where adding/removing a dot changes the implemented Boolean expression. Why Other Options Are Wrong: Non-changeable: contradicts programmability. Intersection of logic blocks: the grid is within a block, not between blocks. I/O point: unrelated to crosspoint programming. Common Pitfalls: Confusing polarity bubbles with programmable dots; bubbles indicate inversion, dots indicate connections. Final Answer: A point that is programmable

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