Digital electronicsLesson 4 of 4 in the course Sequential logic

Digital Counters: State Sequences, Architectures, and Applications

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

A digital counter is a sequential logic circuit that stores a count and changes it in response to clock transitions. This lesson introduces the counter’s basic structure, signals, output encodings, and modulus.

A counter is a finite-state machine. Its flip-flops store the current state, and its outputs represent that state as a count. On each qualified active clock edge, an up-counter usually increases its count by one; a down-counter decreases it by one. When a counting sequence reaches its endpoint, the next clock can cause rollover: the sequence wraps to its beginning.

All flashcards

What is a digital counter?
A clocked sequential circuit whose state represents a count and changes according to a specified sequence.
What is rollover?
The wraparound that occurs when the next count event after the sequence's endpoint returns the counter to its beginning.
What does a count enable do?
It allows counting when asserted and inhibits counting when deasserted.
What is the modulus of a counter?
The number of distinct states in one complete counting sequence.
What is a Johnson counter?
A circular shift register that feeds the inverted output of its final stage back to its first stage.

Quiz questions

  1. How are the flip-flops clocked in a synchronous counter?Answer: They share a common clock and respond to its active edge.
  2. In a binary ripple counter, how does each stage's output frequency compare with its input frequency?Answer: It is half the input frequency.
  3. What is the usual modulus of a ring counter with nn flip-flops?Answer: nn states.
  4. What is the usual modulus of a Johnson counter with nn flip-flops?Answer: 2n2n states.
  5. A counter-based PWM has Period = 11 and Width = 3. What is its duty cycle?Answer: 25%.

Based on the Wikipedia article Counter (digital), licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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