Question 1

Serial in / Serial out (SISO) 8-bit shift register timing An 8-bit SISO shift register is clocked at 150 kHz. What is the time delay from the serial input to the Q3 tap (after four stages)?

Accepted Answer

Introduction / Context: Shift registers propagate data one stage per clock. The delay to a particular tap equals the number of stages to that tap multiplied by the clock period. This is a core timing idea in digital design and serial interfaces. Given Data / Assumptions: Clock frequency f = 150 kHz. Tap Q3 is four stages from the serial input. Each clock advances data by one stage. Concept / Approach: Clock period T = 1 / f. Time to reach Q3 = 4 * T, because the bit must traverse four flip-flops. Step-by-Step Solution: T = 1 / 150,000 = 6.666... µsDelay to Q3 = 4 * T = 4 * 6.666... µs = 26.666... µsRounded to 26.67 µs Verification / Alternative check: Dimensional check: kHz implies microsecond periods. Four microsecond-scale periods give a few tens of microseconds, which matches 26.67 µs and not milliseconds. Why Other Options Are Wrong: 1.67 µs: Too small; equals roughly T/4, not 4T. 26.7 ms / 267 ms: Millisecond values are three orders of magnitude too large for a 150 kHz clock. Common Pitfalls: Mistaking the number of stages (three vs. four) for Q3. Mixing kHz with ms instead of µs during unit conversion. Final Answer: 26.67 µs

Question 2

Timing sequence generation – choosing the counter type Which counter is commonly used to generate a sequence of equally spaced timing pulses for control logic?

Accepted Answer

Introduction / Context: Digital systems often need evenly spaced timing phases for sequencing (e.g., stepper processes, multiplexing). Choosing the right counter simplifies decoding and ensures nonoverlapping, uniform timing windows. Given Data / Assumptions: We want multiple distinct timing pulses across a cycle. Uniform spacing and simple decoding are desired. Concept / Approach: A Johnson counter (twisted ring) produces 2n unique nonoverlapping states from n flip-flops. Its outputs are easy to decode into equally spaced phases, making it ideal for timing sequences. Ring counters are similar but yield only n states; binary counters require more decoding logic for equal-phase timing signals. Step-by-Step Solution: Identify the requirement: equally spaced timing pulses.Recall Johnson counter property: 2n uniformly distributed states with simple decoding.Select Johnson counter as the best fit. Verification / Alternative check: Design handbooks recommend Johnson counters for timing/sequence generation because each output remains high for exactly n clocks in a 2n cycle, yielding clean, evenly spaced phases. Why Other Options Are Wrong: Ring shift: Provides n states; fewer phases and less flexibility than Johnson for the same number of flip-flops. Clock: Not a counter type; it is the timing source itself. Binary: Requires additional decoding to achieve equally spaced, nonoverlapping pulses. Common Pitfalls: Assuming a plain binary counter automatically provides equal, nonoverlapping timing phases without extra logic. Final Answer: Johnson

Question 3

SISO delay design – choosing clock for a required delay An 8-bit serial in/serial out shift register must provide a 20 µs total delay from input to serial output. What clock frequency is required?

Accepted Answer

Introduction / Context: Shift registers are often used as delay elements. The total delay equals the number of stages times the clock period. Selecting the correct clock frequency is a common timing-design task. Given Data / Assumptions: 8-bit SISO shift register. Required overall delay = 20 µs. Each clock advances data by one stage. Concept / Approach: Total delay = N * T, where N is the number of stages and T is the clock period. Frequency f = 1 / T. Solve for f using N = 8 and total delay given. Step-by-Step Solution: Total delay = N * T = 20 µsSo, T = 20 µs / 8 = 2.5 µsFrequency f = 1 / T = 1 / 2.5 µs = 400 kHz Verification / Alternative check: Sanity check: An 8-stage pipeline at 400 kHz has period 2.5 µs; 8 periods is 20 µs, exactly as required. Why Other Options Are Wrong: 40 kHz: Ten times too low; would yield 200 µs delay. 50 kHz: Too low; delay would be 160 µs. 500 kHz: Too high; delay would be 16 µs. Common Pitfalls: Confusing 'bits' with 'bytes' or forgetting that each stage adds one full clock period. Unit conversion errors between µs and kHz. Final Answer: 400 kHz

Question 4

Bus interfacing – alternative to individual tri-state outputs Another common way to connect multiple devices to a shared data bus is to use a ________.

Accepted Answer

Introduction / Context: Shared data buses require controlled bidirectional paths. Besides discrete tri-state drivers, integrated bus transceivers provide direction control and high-impedance states to prevent contention. Given Data / Assumptions: Multiple devices share a common data bus. Need controlled bidirectional data flow and isolation. Concept / Approach: A transceiver integrates transmitter and receiver functions with direction (DIR) and output enable (OE) controls, simplifying bus connections and ensuring safe handover between talkers and listeners. Step-by-Step Solution: Identify the device class that supports bidirectional bus driving with high-Z control.Select 'transceiver' as the appropriate answer. Verification / Alternative check: Popular parts (e.g., 74HC245) are advertised as octal bus transceivers precisely for this role. Why Other Options Are Wrong: circulating gate: Not a standard bus component. bidirectional encoder: Encoders/decoders translate codes; they do not provide controlled high-Z bus driving. strobed latch: Provides storage and gating but not robust bidirectional bus driving with direction control. Common Pitfalls: Assuming any latch or buffer can replace a transceiver on a bidirectional bus. Final Answer: transceiver

Question 5

Universal/parallel-access shift register capabilities A 74HC195 4-bit parallel-access shift register can be configured to operate in which of the following ways?

Accepted Answer

Introduction / Context: Universal/parallel-access shift registers offer flexible data movement modes, enabling them to interface with both serial and parallel subsystems. Recognizing these modes is key for glue logic design. Given Data / Assumptions: Device: 74HC195 (parallel access shift register). Supports shifting and parallel loading. Concept / Approach: Such registers typically allow serial input with serial output (SISO), serial input with parallel output (SIPO), and parallel input with serial output (PISO). Control inputs select between load and shift operations, and outputs can be tapped in serial or parallel form. Step-by-Step Solution: Identify that parallel access plus shift capability implies multiple modes.Confirm serial paths and parallel output taps exist.Conclude that all listed modes are supported. Verification / Alternative check: Datasheet block diagrams show parallel inputs with a load control and serial input path through the flip-flop chain, as well as both serial and parallel outputs. Why Other Options Are Wrong: Each single mode alone is not exclusive; the device does not limit you to only one of them. Common Pitfalls: Confusing a basic SISO register with a universal/parallel-access type that supports load and different I/O tap configurations. Final Answer: all of the above

Question 6

Three-state buffer purpose in bus systems What is the primary purpose of using a three-state (tri-state) buffer in a shared data bus architecture?

Accepted Answer

Introduction / Context: In bused systems, many devices share lines. A three-state buffer lets only one device drive the bus at a time, preventing contention. Understanding its primary role helps in designing reliable bus interfaces. Given Data / Assumptions: Shared data bus with multiple potential drivers. Buffers can be enabled or disabled to present high impedance. Concept / Approach: Tri-state buffers have an enable control. When enabled, they pass data; when disabled, they present a high-impedance output (effectively disconnected). This gating of drive onto the bus is fundamentally about controlling data flow and bus access. Step-by-Step Solution: Identify the bus requirement: only one active driver at a time.Use the buffer’s enable to grant or revoke bus drive.Therefore, the primary purpose is controlled data flow (arbitration) on the bus. Verification / Alternative check: System timing diagrams show OE (output enable) signals orchestrating which device drives the bus in each time slot—core to data flow control. Why Other Options Are Wrong: Isolation (a): A tri-state does isolate when disabled, but isolation is a consequence; the primary system-level goal is controlled data flow. Provide sink/source current (b): That is a line-driver strength consideration, not the defining purpose of tri-state behavior. Temporary storage (c): Buffers do not store like latches/flip-flops. Common Pitfalls: Equating tri-state drivers with simple buffers and overlooking the OE-controlled high-Z state. Final Answer: to control data flow

Question 7

Johnson counter fundamentals In a 4-bit Johnson (twisted-ring) counter, how many distinct states (bit patterns) occur in one full sequence?

Accepted Answer

Introduction / Context: Johnson counters are popular for generating multiple evenly spaced timing phases with minimal decoding. Knowing the number of states helps size the counter for a desired number of phases. Given Data / Assumptions: Counter type: 4-bit Johnson counter. Feedback is inverted (twisted ring). Concept / Approach: An n-bit Johnson counter cycles through 2n unique states. For n = 4, that is 8 distinct patterns, doubling what a regular ring counter would produce with the same number of flip-flops. Step-by-Step Solution: Number of states = 2 * n = 2 * 4 = 8 Verification / Alternative check: Enumerating the sequence shows the output walks through eight unique nonoverlapping patterns before repeating, used commonly to create 8-phase timing signals from four flip-flops. Why Other Options Are Wrong: 1 or 2: Far too small; even a fixed or toggle state machine exceeds these counts. 4: This would be the count for a 4-stage ring (not twisted) counter, not a Johnson counter. Common Pitfalls: Confusing Johnson with simple ring counters. Assuming 2^n states as in a binary counter; Johnson uses 2n states. Final Answer: 8

Question 8

Digital computer architecture — internal data format In modern computer architecture, data is processed internally in which format within the CPU and on its core datapaths?

Accepted Answer

Introduction / Context: Inside a computer, the central processing unit (CPU) moves and transforms data across registers, arithmetic logic units (ALUs), and internal buses. Although many external interfaces (for example, UART, SPI) use one-bit-at-a-time transmission, the CPU's core operations rely on multi-bit words being handled simultaneously. This question checks whether you recognize that internal computation is fundamentally parallel rather than serial. Given Data / Assumptions: Typical word sizes (8, 16, 32, 64 bits) are manipulated as a group. ALU operations (add, AND, shift) act on entire words in one clock operation. External or peripheral links may still be serial for pin-count and distance reasons. Concept / Approach: Parallel operation means multiple bits are processed in the same clock event along dedicated bit-slices or wide datapaths. This enables high throughput and deterministic latency for arithmetic and logic. Serial operation inside the CPU would require cycling bit-by-bit through the same hardware, significantly reducing performance for general-purpose processing. Step-by-Step Solution: Identify how arithmetic works: adders, shifters, and logic units are built as multi-bit structures (ripple-carry, carry-lookahead, etc.).Observe register files: they read/write full words (many bits) at once.Internal buses: 32-bit, 64-bit or wider, moving many bits each cycle → parallel.Therefore, internal CPU data handling is parallel by design. Verification / Alternative check: Microarchitecture diagrams consistently show N-bit ALUs and N-bit registers. Even superscalar and vector units expand parallelism further (SIMD lanes), reinforcing that internal processing is parallel. Why Other Options Are Wrong: Tristate: Describes an output driver mode (HIGH, LOW, Hi-Z), not a data-processing format. Universal: Not a standard data format term in this context. Serial: Used on external links and some special engines but not the main CPU datapaths. Common Pitfalls: Confusing external serial peripherals with internal CPU architecture. Assuming “serial” saves hardware; CPUs prioritize speed with parallel words. Final Answer: Parallel

Question 9

Shift registers — identifying unsupported modes Which of the following is not a standard, meaningful transfer characteristic of a shift register?

Accepted Answer

Introduction / Context: Shift registers are sequential circuits that move data one bit per clock along a chain of flip-flops. They are categorized by how data enters (serial or parallel) and how data leaves (serial or parallel). Understanding valid input/output pairings helps you recognize common parts like SISO, SIPO, PISO, and PIPO devices. Given Data / Assumptions: SIPO: serial-in/parallel-out (e.g., 74HC595). PISO: parallel-in/serial-out (e.g., 74HC165). PIPO: parallel-in/parallel-out (used more as register files/temporary storage). SISO: serial-in/serial-out (basic shifter). Concept / Approach: A valid label describes one input mode and one output mode. “Serial in / parallel in” describes two input methods without specifying how the data exits, so it isn’t a coherent or standard characterization of a shift-register transfer mode. By contrast, SIPO, PISO, and PIPO describe a clear input-to-output relationship. Step-by-Step Solution: List known, standard types: SISO, SIPO, PISO, PIPO.Check each option against these standard categories.Find the option that does not pair input with an output method: “Serial in / parallel in.”Therefore, it is not a valid/standard mode description. Verification / Alternative check: Datasheets and textbooks uniformly use SISO, SIPO, PISO, and PIPO nomenclature. There is no conventional “SI/PI” category because that phrase does not define an output behavior. Why Other Options Are Wrong: Serial in / parallel out: SIPO is common for expanding outputs from microcontrollers. Parallel in / serial out: PISO is used to read multiple inputs with few pins. Parallel in / parallel out: PIPO acts as a register/temporary storage with parallel transfer. Common Pitfalls: Misreading “in/out.” Each standard label must pair one input mode with one output mode. Assuming any two descriptors form a valid mode; they must describe input and output, not both inputs. Final Answer: Serial in / parallel in

Question 10

Magnetic materials – is a ferromagnetic material one that “forms a resistance” to magnetic fields?

Accepted Answer

Introduction / Context: While this topic appears under shift-registers, it references basic physics of materials. Ferromagnetism is a material property crucial to transformers, inductors, and magnetic storage. The statement suggests that ferromagnetic materials “form a resistance to magnetic fields,” which confuses electrical resistance with magnetic behavior. Given Data / Assumptions: Ferromagnetic materials include iron, cobalt, nickel, and alloys. Key traits: large positive magnetic susceptibility and domain alignment. Temperature can affect ferromagnetism (Curie temperature), but the definition remains. Concept / Approach: Ferromagnetic materials strongly attract magnetic fields and can retain magnetization due to domain alignment; they do not resist magnetic fields in the sense implied. A more appropriate term in magnetics is reluctance, the magnetic analog of resistance, but ferromagnetic cores are used precisely because they offer low reluctance paths that concentrate flux, not high “resistance.” The statement therefore mischaracterizes ferromagnets and conflates electrical resistance with magnetic circuit concepts. Step-by-Step Solution: 1) Define ferromagnetism: strong, cooperative alignment of magnetic moments.2) Practical effect: high permeability (mu) → easy flux conduction.3) Compare to paramagnetic/diamagnetic: much weaker effects than ferromagnetic.4) Conclude: they do not “form resistance” to fields; they guide and amplify flux. Verification / Alternative check: In transformers, ferromagnetic cores concentrate magnetic flux and reduce magnetizing current—behavior opposite to “resisting” a magnetic field. The B–H curve shows high permeability regions where small applied field produces large flux density. Why Other Options Are Wrong: “Correct” flips physics. Temperature and initial magnetization do not turn ferromagnets into field resistors. Electrical resistivity is a different material parameter from magnetic permeability. Common Pitfalls: Mixing up electrical resistance with magnetic reluctance/permeability; assuming “ferro” means blocking fields. Remember: ferromagnets are chosen to channel magnetic flux. Final Answer: Incorrect

Question 11

Counters vs shift registers – is it true that a counter has a fixed state sequence but a shift register does not?

Accepted Answer

Introduction / Context: Digital designers often differentiate counters and shift registers by their behavior across clock cycles. The statement claims that counters have a specified sequence while shift registers do not. This is misleading because many shift-register applications (ring, Johnson) also have well-defined state sequences. Given Data / Assumptions: Counters step through numeric sequences (binary, Gray, mod-N). Shift registers move stored bits left/right, optionally with feedback. Some shift-register configurations explicitly define state loops. Concept / Approach: A counter indeed has a predetermined state progression by design (for example, 0000 → 0001 → 0010 …). But a simple shift register loaded with a known seed and feedback forms specific sequences: a ring counter circulates a single 1; a Johnson counter circulates a pattern of ones and zeros; LFSRs produce maximal-length pseudo-random sequences with exact, repeatable order. Therefore, it is inaccurate to say shift registers do not have specified sequences—they often do when designed as counters using shift topology. Step-by-Step Solution: 1) Recognize counters implement state machines with next-state logic.2) Recognize shift registers plus feedback also implement state machines.3) Provide examples: ring and Johnson counters (shift-based) have explicit sequences.4) Conclude the statement is false. Verification / Alternative check: Datasheets label devices like 74HC4017 (Johnson decade counter) or 74HC194 (bidirectional shift register) that can be wired to form counters with deterministic sequences. Texts treat these as shift-register-derived counters. Why Other Options Are Wrong: “Correct” ignores common shift-register counters. Asynchronous/synchronous qualifiers and clock duty cycle do not decide whether a sequence is specified; design and feedback do. Common Pitfalls: Assuming “shift register” always means arbitrary data movement. With feedback and initialization, they become deterministic sequence generators. Final Answer: Incorrect

Question 12

Parallel-to-serial transmission – must parallel data be converted into serial format before sending over a serial link?

Accepted Answer

Introduction / Context: Many systems collect data in parallel (multiple bits at once) but transmit over a single-wire or differential serial channel (UART, SPI single line, SERDES lanes). This raises a practical requirement: can parallel words traverse a serial medium directly, or must they be serialized first? Given Data / Assumptions: Source presents N-bit words simultaneously. Channel offers one bit path per unit interval (serial). We assume conventional digital transmission without exotic multi-wire bundling. Concept / Approach: A serial channel carries one bit per symbol time (per lane). Therefore, an N-bit parallel word must be converted to a time-ordered sequence of bits. The hardware block that does this is a parallel-in serial-out (PISO) shift register or a serializer. At the receiver, a serial-in parallel-out (SIPO) stage reconstructs the word boundaries. This conversion is independent of parity, speed grade, or cable impedance; those affect signal integrity and framing, not the necessity of serialization. Step-by-Step Solution: 1) Latch an N-bit parallel word.2) Shift bits out in a defined order (MSB-first or LSB-first) via a PISO.3) Send over the serial medium with appropriate clocking/encoding.4) At the receiver, SIPO collects bits per clock and presents them in parallel again. Verification / Alternative check: UARTs, SPI, I2C, and high-speed SERDES all embody the same principle: data is serialized before line transmission and deserialized after reception, even if higher-level framing differs. Why Other Options Are Wrong: Parity mode, data rate, or cable impedance does not remove the need to serialize; they address error detection and physical layer aspects. Saying “Incorrect” would deny the definition of a serial channel. Common Pitfalls: Confusing multiple serial lanes aggregated in parallel (e.g., x4 links) with true parallel buses; each lane is still serial and requires serialization at some stage. Final Answer: Correct

Question 13

74194 universal shift register – is one major differentiator the presence of separate serial inputs for shifting left and shifting right?

Accepted Answer

Introduction / Context: The 74194 (and HC/HCT variants) is a bidirectional universal shift register commonly studied in digital logic courses. Recognizing its distinguishing features helps you choose appropriate parts and wire correct data paths in lab exercises and designs. Given Data / Assumptions: Device supports parallel load and bidirectional shifting. Control inputs select hold, shift-left, shift-right, or parallel load modes. We focus on where incoming serial bits are sourced for each shift direction. Concept / Approach: The 74194 provides separate serial inputs for left and right shifts. When configured to shift right, data enters from the serial-right input; for shift left, data enters from the serial-left input. This avoids having to externally multiplex a single serial input and simplifies direction control. Combined with synchronous parallel load, the chip is termed “universal.” Step-by-Step Solution: 1) Set mode via S0/S1 (or equivalent) to select shift left or shift right.2) For right shifts, feed new bits on the SR input; for left shifts, on the SL input.3) On the active clock edge, internal stages shift and capture the selected serial input.4) Verify using datasheet timing diagrams and truth tables. Verification / Alternative check: Manufacturer datasheets show distinct serial inputs and a mode table indicating which input is sampled for each shift direction. Lab experiments with LEDs on Q outputs readily confirm directional shifting behavior. Why Other Options Are Wrong: CMOS vs TTL families preserve the logical interface. Output enable and supply voltage do not change the existence of two serial inputs. Common Pitfalls: Swapping the serial inputs or neglecting to set the mode lines correctly, which makes the register appear nonfunctional or shifting the wrong way. Final Answer: Correct

Question 14

Register building blocks – does a single stage of a typical synchronous register consist of a latch rather than an edge-triggered flip-flop?

Accepted Answer

Introduction / Context: The term “register” in synchronous digital design usually denotes a bank of edge-triggered storage elements that capture data on a specific clock edge. The statement claims that a register stage is a latch, which invites clarification of latches versus flip-flops and common implementation practices. Given Data / Assumptions: Synchronous pipelines target edge-aligned timing (setup/hold to a single edge). Commodity standard-cell libraries and TTL/CMOS parts expose D flip-flops as the canonical register element. Latches are level-sensitive and used deliberately in certain timing methodologies. Concept / Approach: A flip-flop is typically built from two latches (master-slave) to achieve edge-triggered behavior. Registers in CPUs, FPGAs, and ASICs are conventionally composed of D flip-flops to simplify timing analysis with a single active edge. While some designs intentionally use latches (two-phase latch-based pipelines), that is a specific methodology. Therefore, a “typical” register stage is a flip-flop, not a single level-sensitive latch. Step-by-Step Solution: 1) Define register (synchronous): storage updated on clock edges.2) Note flip-flop = edge-triggered; latch = level-sensitive.3) Common practice: implement registers using D flip-flops for robust edge-based timing.4) Conclude the statement is false in the usual synchronous context. Verification / Alternative check: FPGA primitives (for example, FDRE in Xilinx) are D flip-flops; library cells are DFFs. Texts show registers as cascaded DFFs, not single latches, for mainstream synchronous design. Why Other Options Are Wrong: Saying “Correct” generalizes latch use improperly. Dynamic shift registers and special latch-based flows are exceptions, not the default. Clock frequency alone does not dictate latch vs flip-flop selection. Common Pitfalls: Conflating internal flip-flop construction (latches inside) with the architectural element used in synchronous design. At the design abstraction, a register is a DFF-based element. Final Answer: Incorrect

Question 15

Ring counter definition – is it a register that “continuously outputs” a fixed bit pattern in parallel rather than circulating a single 1 (or pattern) through its stages?

Accepted Answer

Introduction / Context: Ring counters are a classic example of counters implemented using shift registers. A clear definition avoids confusion between “parallel outputs” (which all registers have) and the behavior of a ring counter, which is about circulating a token through stages over time. Given Data / Assumptions: A ring counter feeds the last stage's output back to the first input. It is initialized with a single 1 (or a known pattern) and clocked. All stage outputs are available in parallel as pins, as with any register. Concept / Approach: What makes a ring counter special is not parallel outputting of a fixed word but the sequential circulation of a 1 (or encoded pattern) through N flip-flops, yielding N distinct one-hot states over N clocks. A Johnson (twisted-ring) counter similarly circulates a complementary pattern, creating 2N distinct states. The phrase “continuously outputted in parallel” mischaracterizes the dynamic nature: the state vector seen at the parallel outputs changes each clock as the token moves; it is not a single, unchanging word continuously driven in parallel. Step-by-Step Solution: 1) Reset register to 000…1 (one-hot).2) On each clock, shift right (or left) and wrap the last bit to the first.3) Observe the outputs: the single 1 moves position each tick, producing a sequence of states.4) Therefore, definition hinges on circulation, not static parallel output. Verification / Alternative check: Timing diagrams show a walking 1 across Q0…Q(N−1). Datasheets for ring/Johnson counters present state tables cycling through positions, not a constant parallel word. Why Other Options Are Wrong: Calling the statement “Correct” confuses static parallel output with dynamic state progression. Johnson counters are related but still circulate patterns; asynchronous clocks would break deterministic sequencing and are not part of the definition; reset polarity is an implementation detail. Common Pitfalls: Equating “has parallel outputs” with “outputs in parallel as a definition.” All registers expose parallel outputs; the special behavior is the rotating one-hot or pattern sequence. Final Answer: Incorrect

Question 16

Shift-register operations: A parallel-load operation is always asynchronous and therefore not dependent on the clock. Evaluate this general claim for shift-register ICs (many families include both synchronous and asynchronous load variants).

Accepted Answer

Introduction / Context: Parallel load in shift registers copies multiple input bits into internal flip-flops in one action. Some ICs implement parallel load synchronously (on a clock edge), while others provide an asynchronous load that overrides shifting regardless of the clock. Treating all parallel loads as asynchronous is an overgeneralization and can lead to design and troubleshooting mistakes. Given Data / Assumptions: Shift registers exist across several logic families and part numbers. Control pins may be named PL, SH/LD, /LD, MR, CE, etc. Datasheet timing explicitly states whether load is synchronous or asynchronous. Concept / Approach: The correct view is device-specific. Universal/bidirectional parts such as classic TTL universal shift registers often use a synchronous parallel load (data enters on the active clock edge when load is asserted). Other parts, like certain serial-parallel registers, expose an asynchronous parallel load that immediately forces the internal state when the load input is asserted, independent of the clock. Therefore, the global statement 'parallel load is asynchronous' is false in general. Step-by-Step Solution: 1) Identify the part number and examine the function table.2) If the table shows loading on a clock edge when Load is active, the load is synchronous.3) If the table shows loading occurs immediately when /PL is asserted (no clock requirement), it is asynchronous.4) Conclude that implementations vary; no single rule covers all devices. Verification / Alternative check: Cross-check multiple register datasheets; you will find both synchronous and asynchronous load implementations, confirming that the blanket claim is incorrect. Why Other Options Are Wrong: “Correct” ignores many synchronous-load devices. Family-based answers (CMOS vs TTL) or enable polarity do not determine synchronous vs asynchronous by themselves. Common Pitfalls: Assuming naming like SH/LD always implies asynchronous behavior; ignoring timing diagrams; overlooking that test benches must match the specific timing model. Final Answer: Incorrect

Question 17

Shift-register feature sets: Evaluate the claim that practically every possible load, shift, and conversion operation is available in a single shift-register IC.

Accepted Answer

Introduction / Context: Shift registers come in many variants: serial-in serial-out, serial-in parallel-out, parallel-in serial-out, universal, bidirectional, with or without asynchronous load, and different enable schemes. Datasheets specify a finite feature set per device. No single IC covers literally every operation and conversion possibility without external logic. Given Data / Assumptions: Diverse part numbers across logic families and vendors. Common operations: parallel load, serial shift left/right, hold, clear, bidirectional control. Conversions: SISO, SIPO, PISO, PIPO realized by different or universal devices. Concept / Approach: Universal shift registers provide broad capabilities (serial and parallel I/O, bidirectional shifting) but still have defined limits. Some conversions may require multiple packages or extra gating (e.g., width expansion, specialized recirculation, Gray/Binary conversions). Therefore the phrase 'practically every possible' is marketing-sounding and not technically accurate as a universal truth. Step-by-Step Solution: 1) Identify the operations you need (e.g., PISO plus bidirectional shift and synchronous clear).2) Check the target device function table; missing modes mean additional logic or a different part is required.3) For uncommon conversions, compose multiple devices or add small glue logic.4) Conclude that one chip cannot guarantee 'every possible' operation. Verification / Alternative check: Compare several universal shift-register datasheets; features vary, and some modes are absent or mutually exclusive. Why Other Options Are Wrong: “Correct” exaggerates device capabilities. “Only true for universal” remains too broad. “True with glue logic” changes the premise to a multi-chip solution. Common Pitfalls: Assuming a 'universal' label equals unlimited capability; not reading function tables closely. Final Answer: Incorrect

Question 18

Definition check: A universal shift register provides both serial and parallel inputs and outputs, supporting multiple load and shift modes. Evaluate this statement.

Accepted Answer

Introduction / Context: Universal shift registers are widely used because they consolidate several data movement modes into one device. Understanding what 'universal' implies prevents misapplication and simplifies design choices in digital systems. Given Data / Assumptions: Device exposes serial inputs/outputs and parallel inputs/outputs. Mode controls select load, shift left/right, and hold. Family-specific timing (synchronous/asynchronous load) applies. Concept / Approach: By offering serial and parallel data paths and directional control, a universal shift register can perform SISO, SIPO, PISO, and PIPO functions, plus bidirectional shifting. This versatility reduces part count and allows easy interfacing between serial links and parallel buses. Step-by-Step Solution: 1) For parallel load, assert the load control per datasheet and capture the bus value.2) For serial shifting, apply data to the serial input and clock per selected direction.3) For parallel output, read the Q outputs; for serial output, monitor the end bit.4) Switch modes to convert between serial and parallel representations. Verification / Alternative check: Function tables for classic universal parts show serial left/right shifting and parallel load with both serial and parallel I/O pins. Why Other Options Are Wrong: Claims of serial-only or parallel-only contradict the 'universal' definition. Common Pitfalls: Ignoring direction control; misreading whether load is synchronous; forgetting that outputs may be registered. Final Answer: Correct

Question 19

Terminology: In the context of shift registers and counters, 'bidirectional' means the device can shift or count in two directions (left/right or up/down). Does it mean 'having two states'?

Accepted Answer

Introduction / Context: Digital terms can be confusingly similar. 'Bidirectional' describes directionality, not the number of states. Misunderstanding this affects how one configures control pins for left/right shifts or up/down counts. Given Data / Assumptions: Devices may include a DIR, U/D, or L/R control. State count is determined by bit width and architecture, not by 'bidirectional' capability. Shift registers and counters can have many states (not just two). Concept / Approach: Bidirectional means the data path or counting sequence can proceed in either of two directions under control. Number of states is unrelated: an n-bit register can represent 2^n states; a Johnson counter has 2n states; a ring counter has n states—none of which change simply because the device is bidirectional. Step-by-Step Solution: 1) Identify the function: shift register or counter.2) Observe the direction control input and its effect on data movement.3) Note the state space is set by architecture and width, not by directionality.4) Conclude that 'two states' is a misinterpretation. Verification / Alternative check: Datasheets label direction pins and show identical state counts regardless of selected direction. Why Other Options Are Wrong: Answers tying bidirectionality to a specific counter type confuse direction with state-cardinality. Common Pitfalls: Equating 'bi-' with binary state rather than dual direction; assuming direction control halves or doubles the number of states. Final Answer: Incorrect

Question 20

Stepper-motor construction claim: 'Digitally controlled stepping' can be achieved by four stator coils arranged as four pole pairs 45° apart and three ferromagnetic rotor pairs spaced 60° apart. Evaluate whether this specific arrangement statement i…

Accepted Answer

Introduction / Context: Stepper motors move in discrete angles set by the interaction between stator pole arrangements and rotor teeth or magnets. Common stepper types (variable reluctance, permanent magnet, hybrid) use carefully matched stator/rotor geometries that yield uniform step angles (e.g., 7.5°, 1.8°). The quoted 45° stator spacing with three ferromagnetic rotor pairs 60° apart is inconsistent with standard stepper design practice. Given Data / Assumptions: Four stator coils as four pole pairs 45° apart (implies 8 poles uniform over 360°). Three rotor pole pairs 60° apart (implies 6 magnetic poles). Goal: digitally controlled discrete stepping. Concept / Approach: Uniform stepping requires specific pole/teeth counts so that sequential excitation advances the rotor by a small, repeatable angle. Typical hybrid steppers use many rotor teeth (e.g., 50) and mated stator teeth to obtain 1.8° steps. A coarse geometry with 45° and 60° spacings would lead to large, uneven torque and non-uniform step angles. Moreover, four stator pole pairs and three rotor pairs with those spacings do not form a standard least-common-multiple pattern that yields consistent small steps. Step-by-Step Solution: 1) Compare to standard designs: hybrid steppers exploit fine tooth counts to achieve small steps.2) Evaluate 45°/60° spacings: these produce 8 and 6 poles respectively, leading to coarse 360/LCM(8,6) = 360/24 = 15° theoretical alignment increments at best, not typical fine steps.3) Practical steppers require precise tooth geometry, not just a few pole pairs at tens of degrees spacing.4) Conclude the described arrangement is not a sound standard for stepper design. Verification / Alternative check: Reference textbooks show tooth-count formulas for step angle: step_angle = 360 * (number_of_phases) / (stator_teeth * rotor_teeth) for certain topologies; the claimed geometry does not match common results. Why Other Options Are Wrong: “Correct” conflicts with established designs; answers tying it to synchronous AC motors or microstepping change the device type or control method rather than validating the geometry. Common Pitfalls: Conflating coarse multi-pole synchronous motors with fine-step steppers; assuming any pole spacing will yield uniform digital steps. Final Answer: Incorrect

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