Ring & Johnson Counters — These are widely used shift-register-based counters (sequence generators), not “uncommon” circuits. Evaluate the statement.
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AIncorrect
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BCorrect
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CTrue only in ASICs
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DTrue only in FPGAs
Answer
Correct Answer: Incorrect
Explanation
Introduction: Ring counters and Johnson (twisted-ring) counters are classic sequence generators built from shift registers. They appear in timing generators, state machines with simple decoding, LED chasers, and clock-division applications. The claim that they are “uncommon” is inaccurate in both education and industry contexts.Given Data / Assumptions:
- Ring counter: a single 1 circulates through a ring of flip-flops.
- Johnson counter: the inverted output of the last stage is fed back to the first, producing 2N distinct states with N flip-flops.
- Synchronous clocking is typical; decoding is straightforward.
Concept / Approach: Because these counters provide easily decodable one-hot or two-hot patterns with low logic overhead, they are favored where simple, glitch-resistant state outputs are needed. Their usage is common in CPLD/FPGA designs and discrete TTL/CMOS projects alike.Step-by-Step Solution:
Recognize ring/Johnson as shift-register feedback topologies.Note applications: timing sequences, divide-by-N chains, LED scanning.Conclude that describing them as “uncommon” is a mischaracterization.Verification / Alternative check:
Survey introductory digital design textbooks and vendor app notes; both cover these counters prominently.Why Other Options Are Wrong:
Correct: Would imply rarity; contradicted by widespread usage.True only in ASICs / FPGAs: Both discrete and programmable logic use them.Common Pitfalls:
Confusing these with binary ripple or synchronous up/down counters; they serve different needs.Overlooking the ease of decoding compared to binary counters.Final Answer:
Incorrect