Question 1

Parallel (synchronous) counters and preset behavior Many parallel, edge-clocked counters employ synchronous presetting, meaning the device loads a preset value on the active transition of the same clock that is used for counting. What is this preset…

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Introduction / Context: Counters are ubiquitous in digital electronics for frequency division, timing, and sequencing. A practical feature found in many devices is the ability to preload a known value before counting proceeds. This question focuses on the method whereby the counter loads that value in step with the normal clocking of the device, a technique especially important for glitch-free startup and for precise modulus control. Given Data / Assumptions: The device discussed is a parallel (synchronous) counter where all flip-flops share a common clock. A preset value is available via parallel inputs. The preset action is initiated by a control signal but occurs on a specified clock transition. Concept / Approach: Presetting can be implemented in two broad ways: asynchronous and synchronous. Asynchronous preset acts immediately when its control is asserted, independent of the clock, which may cause hazards or violate timing in downstream logic. In contrast, synchronous preset waits for the designated active clock edge (rising or falling) to update the internal state, thereby aligning the load with the device’s normal timing and minimizing glitches. Step-by-Step Solution: Identify the method: preset occurs on the same edge that advances the count.Match the definition: actions that occur in lockstep with the clock are “synchronous.”Therefore, the named technique is synchronous presetting. Verification / Alternative check: Examine typical synchronous counter datasheets (for example, families like 74HC163/193): the preset/load input is sampled on the active clock transition, guaranteeing controlled state changes that are easy to analyze and simulate. Why Other Options Are Wrong: “Feedback” is a generic concept and not a preset method. “Ripple” refers to asynchronous counting, not preset. “Asynchronous” preset acts immediately and not on the clock edge. Common Pitfalls: Confusing synchronous preset (edge-aligned) with asynchronous load; overlooking the need to satisfy setup/hold on the parallel data when using synchronous load. Final Answer: synchronous

Question 2

One-shot (monostable) fundamentals The technique used by one-shot circuits to respond to a change in signal edge rather than the sustained level is known as what?

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Introduction / Context: A one-shot, or monostable multivibrator, produces a fixed-duration pulse in response to an input event. The essential idea is that the circuit should react to the transition (edge) of the input, not to how long the input remains high or low. This is vital for pulse shaping, debouncing, and timing generation. Given Data / Assumptions: We are discussing monostable (one-shot) behavior. The desired response is to an edge (rising or falling) rather than a steady level. The output is a single pulse of controlled width. Concept / Approach: Edge sensitivity prevents double triggering caused by a long or noisy level. By detecting a 0→1 or 1→0 change, the one-shot ensures a single, predictable output pulse width set by R*C timing in analog designs or by a counter/timer in digital logic. The industry term for reacting to an edge is “edge triggering.” Step-by-Step Solution: Identify required behavior: respond to transitions only.Associate with standard terminology: “edge triggering.”Conclude that the correct term is edge triggering. Verification / Alternative check: Datasheets for retriggerable and non-retriggerable monostables specify whether they trigger on rising, falling, or both edges, confirming the centrality of edge triggering to one-shot design. Why Other Options Are Wrong: “Level management” implies level sensitivity, not edge response. “Trigger input” names a pin, not a technique. “Edge trapping” is not a standard term in this context. Common Pitfalls: Confusing edge-triggered with level-triggered behavior; ignoring input conditioning that prevents false edges due to noise. Final Answer: edge triggering

Question 3

Best oscilloscope trigger for viewing a 4-bit counter timing diagram When examining a 4-bit counter with an oscilloscope to draw its timing diagram, which signal is generally the most reliable to use as the trigger source for stable display?

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Introduction / Context: Obtaining a clean, repeatable timing diagram on an oscilloscope requires a stable trigger reference. In counters, many nodes are derived signals that change at different rates. Choosing the correct trigger source prevents jittery or drifting waveforms on the screen and makes edge relationships easy to interpret. Given Data / Assumptions: The device is a 4-bit counter with a single input clock. Outputs (LSB through MSB) toggle at different submultiples of the clock. We want a stable, periodic trigger that does not skip or wander. Concept / Approach: The clock is the fundamental timing reference for the counter and has the highest and most regular transition rate. Triggering on the clock guarantees each sweep starts at an identical phase of the system. Triggering on an output (especially MSB) can be acceptable, but its lower frequency makes the display more susceptible to drift and makes it harder to capture all intermediate transitions cleanly. Step-by-Step Solution: Identify the available signals: clock, LSB, MSB.Select the signal with the most consistent, frequent edges: the clock.Use the clock as the trigger, then probe outputs to produce a stable timing diagram. Verification / Alternative check: Experienced lab practice prefers clock triggering for sequential circuits; data sheets and application notes often show timing diagrams referenced to the clock edge. Why Other Options Are Wrong: MSB and LSB are slower, derived signals and can cause unstable triggering. A “composite” trigger is nonstandard and unnecessary for basic timing diagrams. Common Pitfalls: Triggering on a glitchy decoded node; setting improper trigger level or slope and mistaking noise for edges. Final Answer: the clock signal

Question 4

Asynchronous counter terminology Asynchronous counters are commonly referred to by what descriptive name in digital electronics literature and datasheets?

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Introduction / Context: Counters are classified as asynchronous or synchronous depending on how their flip-flops are clocked. Understanding the widely used terminology helps when reading datasheets, app notes, or textbooks, and when selecting a device suitable for speed and decoding requirements. Given Data / Assumptions: Asynchronous counters are constructed by daisy-chaining the clock: the output of one flip-flop provides the clock to the next. The chain introduces cumulative delay. Outputs change at slightly different times as state transitions propagate. Concept / Approach: Because edges propagate from stage to stage, the visible switching “ripples” through the flip-flops. This behavior explains the common name “ripple counters.” The term distinguishes them from synchronous counters, in which all stages receive the same clock edge simultaneously and change in parallel (subject to clock-to-Q delay). Step-by-Step Solution: Identify architecture: Q of one stage clocks the next.Observe behavior: sequential, staggered toggling appears like a ripple.Conclude the accepted descriptive name: ripple counter. Verification / Alternative check: Any logic text or vendor datasheet (e.g., 74HC393) refers to asynchronous designs as ripple counters and notes decoding glitches during transitions. Why Other Options Are Wrong: “Toggle” describes how a single T flip-flop behaves, not the counter class. “Binary” describes numbering base, not clocking method. “Flip-flop” is a building block, not a counter type. Common Pitfalls: Assuming ripple counters are adequate for high-speed or glitch-sensitive decoding; forgetting to register decoded outputs when hazards matter. Final Answer: ripple

Question 5

Ripple counter fault analysis In a 4-bit ripple counter, the second flip-flop has failed and is locked (stuck) so it no longer toggles. What will happen to the third and fourth stages of the chain?

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Introduction / Context: Ripple counters rely on a chain where each flip-flop’s output clocks the next stage. Understanding failure effects is useful for troubleshooting. If a stage becomes stuck and ceases to toggle, the fate of subsequent stages depends on how they receive their clocks. Given Data / Assumptions: We have a standard ripple (asynchronous) counter. The second flip-flop’s Q output is the clock source for the third stage. “Locked up” means the second stage Q no longer provides transitions. Concept / Approach: In a ripple design, stage n+1 toggles only when stage n changes state. If stage n stops toggling, it stops delivering clock edges downstream. Without edges, subsequent stages cannot transition and their counts freeze at whatever state they were last in. Step-by-Step Solution: Identify the clock path: CLK3 comes from Q2; CLK4 comes from Q3.Second stage locked → no rising/falling edges on Q2.No edges on Q2 → third stage receives no clock → Q3 remains constant.No edges on Q3 → fourth stage receives no clock → Q4 remains constant. Verification / Alternative check: A timing diagram with Q2 stuck shows Q3 and Q4 flatlined. In-circuit observation with a scope would reveal no transitions downstream. Why Other Options Are Wrong: “Continue to count” is impossible without clock edges. “Incorrect outputs” implies activity; with no clocks there is none. “Molten silicon” is humorous but not an engineering outcome. Common Pitfalls: Confusing ripple with synchronous counters (which share a common clock); in synchronous designs, a single stage failure may not block the clock to others. Final Answer: stop counting

Question 6

Eliminating decoder spikes in counter systems A dependable technique for suppressing short, unwanted pulses (glitches) on decoded outputs is commonly called what?

Accepted Answer

Introduction / Context: When decoding counter outputs, asynchronous transitions can momentarily produce incorrect decode combinations, observed as narrow spikes. Designers routinely mitigate these glitches to prevent false triggering of actuators, displays, or logic that follows. Given Data / Assumptions: We are decoding a multi-bit counter output with combinational logic. Due to ripple delays, intermediate non-valid codes can appear during transitions. Goal: prevent downstream circuits from reacting to those brief spikes. Concept / Approach: “Strobing” is the practice of gating the decoded output with a timing signal that only enables observation when the counter outputs are known to be stable. Typically, the strobe is derived from the clock or from a registered (synchronous) version of the decode. By ensuring the enable window occurs after propagation delays settle, spikes are masked. Step-by-Step Solution: Identify when outputs are valid relative to the clock edge.Generate a strobe/enable pulse in the valid window.AND the decoded lines with the strobe so only stable data passes. Verification / Alternative check: Scope measurements show spikes disappear at the gated node, while the raw decode still exhibits hazards. Synchronous registering of the decode is an equivalent approach. Why Other Options Are Wrong: “Feeding,” “wagging,” and “waving” are not recognized techniques in this context. Common Pitfalls: Setting the strobe window too early (before signals settle); forgetting to account for temperature and process variations in propagation delays. Final Answer: strobing

Question 7

Observing ripple-counter decode glitches on an oscilloscope A glitch on a decoded output of a ripple counter is often hard to see on a scope primarily because ________.

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Introduction / Context: Ripple counters produce short-lived hazards on decoded outputs when multiple bits transition non-simultaneously. Capturing these glitches on an oscilloscope can be challenging. Understanding why helps in choosing measurement techniques and in designing mitigation strategies. Given Data / Assumptions: We are observing a decoded node driven by combinational logic from ripple counter outputs. During state changes, intermediate codes can assert unintended outputs briefly. Oscilloscope persistence and bandwidth affect visibility of narrow pulses. Concept / Approach: The glitches arise due to propagation delay differences and are typically only a few nanoseconds wide (depending on technology). Such brief events have low energy and can be missed without adequate bandwidth, sample rate, or triggering. While decode glitches occur predictably at transitions, their brevity is the primary reason they are hard to see. Step-by-Step Solution: Recognize that hazard pulses are narrow in time.Realize that a scope needs sufficient bandwidth and proper edge triggering on the decoded node to capture them.Conclude that short duration (very fast) is the key difficulty. Verification / Alternative check: Using a high-bandwidth scope with infinite persistence or a glitch capture mode reveals the pulses more readily. A logic analyzer with glitch detection can also help. Why Other Options Are Wrong: Glitches are not random; they correlate with count transitions. They are indeed less frequent than the steady output, but frequency alone does not prevent viewing; the real obstacle is pulse width (speed). “All of the above” is incorrect because “random” is false. Common Pitfalls: Insufficient timebase or trigger settings; probing with excessive capacitance that masks high-speed content. Final Answer: it is very fast

Question 8

Shift-register counters and topology Shift-register-based counters depend on ________, meaning the output of the last flip-flop is routed back to the first flip-flop in a defined manner.

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Introduction / Context: Some counters are built from shift registers rather than from dedicated counter structures. Examples include ring counters and Johnson (twisted-ring) counters. Their operation depends on recirculating data so that a pattern cycles through the register stages. Given Data / Assumptions: A shift register is composed of cascaded flip-flops clocked together. To create a sequence, the end output is routed back to the input in some form. The recirculation may be direct or inverted depending on the desired sequence. Concept / Approach: The general term for routing an output back into an earlier point in the circuit is “feedback.” Ring counters use direct feedback of a single 1 (or 0), while Johnson counters use inverted feedback to generate 2n distinct states from n stages. Without feedback, data would simply shift out and be lost rather than forming a repeating sequence. Step-by-Step Solution: Identify architecture: shift-register stages clocked in parallel.Recognize need for a closed loop to repeat a pattern.Name the technique: feedback. Verification / Alternative check: State sequences for ring and Johnson counters clearly show the role of the looped connection. Timing diagrams confirm that after n or 2n steps the initial pattern reappears. Why Other Options Are Wrong: “MOD” refers to modulus, not topology. “Strobing” is a glitch-masking technique. “Switchbacks” is not standard terminology. Common Pitfalls: Mixing up direct vs. inverted feedback; neglecting initialization so that the register does not enter a valid sequence. Final Answer: feedback

Question 9

Frequency at the MSB of a 4-bit binary up counter A 4-bit binary up counter is clocked at 20 kHz. What output frequency appears at the most significant bit (MSB)?

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Introduction / Context: Binary counters divide frequency by powers of two at successive bit positions. Knowing the division at each bit is essential for generating timing references and subclocks from a master clock. Given Data / Assumptions: 4-bit binary up counter with input clock f_in = 20 kHz. Bit 0 (LSB) toggles every clock edge, dividing by 2. Each more significant bit divides the input frequency by an additional factor of 2. Concept / Approach: For an n-bit binary counter, the frequency at bit k (starting at k = 0 for LSB) is f_in / 2^(k+1). The MSB of a 4-bit counter is bit 3, so its frequency is f_in / 2^4. Step-by-Step Solution: Compute divisor for MSB (bit 3): 2^4 = 16.Calculate f_out = 20 kHz / 16.20,000 Hz / 16 = 1,250 Hz = 1.25 kHz. Verification / Alternative check: A short truth-table or timing sketch shows the LSB toggling each edge (10 kHz), next bit at 5 kHz, then 2.5 kHz, and MSB at 1.25 kHz, confirming the calculation. Why Other Options Are Wrong: 2.50 kHz corresponds to bit 2, not the MSB. 160 kHz and 320 kHz exceed the input frequency and are impossible for a divider. Common Pitfalls: Off-by-one errors in the power of two; confusing toggle rate with full period; mixing Hz and kHz units. Final Answer: 1.25 kHz

Question 10

Identify the counter type from a typical ripple-clocked diagram (no figure provided): Assume the shown circuit uses edge-triggered flip-flops connected in a cascaded (ripple) fashion with the first stage clocked by an external signal and the next st…

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Introduction / Context: Counter identification questions test your understanding of how flip-flops are interconnected. Without the original figure, we apply the Recovery-First Policy and infer the most common textbook arrangement: a minimal ripple (asynchronous) counter using two cascaded flip-flops where the output of one stage clocks the next. Given Data / Assumptions: First flip-flop is clocked by an external clock. Second flip-flop is clocked by the output (usually Q) of the first stage. No additional gating suggests synchronous decoding is absent. Only two stages are implied, producing 2 bits of count (00 to 11). Concept / Approach: In an asynchronous (ripple) counter, not all flip-flops share the same clock; instead, each subsequent stage is triggered by the previous stage's transition. With two flip-flops, the modulus is 2^2 = 4, representing a two-bit counter. Synchronous counters require a common clock and added gating logic to drive each T or J-K input simultaneously. Step-by-Step Solution: Recognize ripple connection: clock of stage 2 is driven by the output of stage 1.Count width: two flip-flops → 2 bits → modulus 4.Absence of shared clock/gating → asynchronous, not synchronous.Therefore, the most reasonable identification is a two-bit asynchronous binary counter. Verification / Alternative check: List the expected output sequence: Q1 (LSB) toggles every clock; Q2 toggles on Q1 transitions → sequence 00, 01, 10, 11, then repeat. Why Other Options Are Wrong: three-bit synchronous binary counter: Requires three stages and a common clock with gating.eight-bit asynchronous binary flip-flop: Size and terminology are incorrect (it would be an eight-bit counter, not a “flip-flop”).four-bit asynchronous binary counter: Would need four stages, not two. Common Pitfalls: Confusing ripple (clock-by-output) with synchronous (common clock).Assuming more bits than actually present in the schematic. Final Answer: two-bit asynchronous binary counter

Question 11

Terminology check: A MOD-10 counter is also called what type of counter? Choose the standard industry name used by datasheets and textbooks.

Accepted Answer

Introduction / Context: Digital counters are often described by their modulus, which is the number of distinct states in the counting sequence. A MOD-10 counter cycles through ten states before rolling over, and there is a widely accepted term for this device. Given Data / Assumptions: MOD-10 means ten valid count states (0 through 9). Terminology is based on long-standing conventions in digital electronics. Concept / Approach: The conventional term for a MOD-10 counter is “decade counter”. Many decade counters also output Binary Coded Decimal (BCD) states, but “decade” is the generic name tied to the modulus itself, independent of output formatting or display usage. Step-by-Step Solution: Identify modulus: 10 → “decade”.Check textbook usage: MOD-10 counters are consistently labeled decade counters.Conclude that “decade” is the accepted answer. Verification / Alternative check: Look at typical TTL/CMOS decade counter datasheets; the description uses “decade” prominently (e.g., BCD decade counter). Why Other Options Are Wrong: strobing: Refers to gating signals to avoid glitches; not a counter type.BCD: A representation format (Binary Coded Decimal), not the name of the modulus class.circuit: Too generic; does not specify type or modulus. Common Pitfalls: Assuming “BCD” is the formal counter name rather than a code format often used with decade counters. Final Answer: decade

Question 12

Using a shift register as a counter — what wiring enables cyclic counting? Select the connection that allows a shift register to recycle a pattern and behave like a simple ring counter.

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Introduction / Context: Shift registers can be turned into counters by feeding their output back to their input, creating circulating patterns. This is the essence of ring counters (and, with logic, Johnson counters), which are special cases of shift-register counters. Given Data / Assumptions: A shift register supports serial-in/serial-out operation. We desire a repeating sequence without external data injection each cycle. Clock shifts the stored pattern along the stages. Concept / Approach: To get a closed loop, connect the serial output back to the serial input. If an appropriate initial pattern (like 1000) is loaded, each clock shifts the 1 through the register and then back to the start, forming a ring counter. For more complex sequences, the feedback can pass through logic (e.g., inversion) to form a Johnson (twisted ring) counter. Step-by-Step Solution: Choose a serial-in/serial-out shift register so bits propagate end-to-end.Connect serial output (Q_out) to serial input (D_in) to close the loop.Initialize a valid seed pattern (not all zeros unless designed otherwise).Clock the register; the pattern circulates → counter-like behavior. Verification / Alternative check: Simulate a 4-bit ring with seed 1000: observe sequence 1000→0100→0010→0001→1000... Why Other Options Are Wrong: A: Merely labels I/O; does not create a loop.B: Parallel inputs are not used continuously in a ring; they are for loading.C: While SISO is useful, the required feature is feedback, not just the SISO type. Common Pitfalls: Forgetting to seed a nonzero pattern leads to a stuck state.Assuming any feedback yields a valid sequence—feedback logic matters for Johnson counters. Final Answer: the serial output of the register is connected back to the serial input of the register

Question 13

When pulses must be counted and displayed in decimal, which counter type is commonly chosen? Select the best match used for decimal readouts and displays.

Accepted Answer

Introduction / Context: Many practical applications, such as frequency counters or event counters, need to display results in base-10. Counters that naturally present their state in decimal-oriented code simplify driving seven-segment displays or decimal readouts. Given Data / Assumptions: The requirement is to display numeric results in base-10. BCD (Binary Coded Decimal) expresses each decimal digit with four binary bits. Display drivers and decoders commonly expect BCD inputs. Concept / Approach: Although “decade” and “BCD” are closely related (a decade counter has ten states), BCD counters explicitly output in a decimal-digit-friendly format. This makes interfacing to BCD-to-7-segment decoders straightforward, which is why BCD counters are often selected when the output is intended for decimal displays. Step-by-Step Solution: Identify need: base-10 display → prefer BCD-coded outputs.Match device: BCD counters output 0000–1001 for digits 0–9.Simplify hardware: BCD-to-7-segment decoder directly converts to display segments.Therefore, BCD counters are commonly used. Verification / Alternative check: Review common parts (e.g., 74xx90/74xx192 families) and application notes; BCD outputs are standard for decimal displays. Why Other Options Are Wrong: Synchronous: Describes timing architecture, not base-10 suitability.Bean: Not a recognized counter type.Decade: Close, but “BCD” better specifies the display-oriented code format expected by decoders. Common Pitfalls: Confusing “decade” (modulus-10) with the code format needed for displays; BCD conveys that format explicitly. Final Answer: BCD

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