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# Ring Counter in Digital Logic

Last Updated on August 30, 2023 by Mayank Dham

Counters are used in a variety of applications in digital logic circuits, ranging from simple counting tasks to more complex sequencing and control operations. The ring counter stands out as an interesting and useful configuration among the various types of counters. A ring counter is a type of shift register with unique characteristics and applications. In this article, we will look at the concept of a ring counter, its working principle, applications, benefits, and the various types available.

## What is Ring Counter in Digital Logic?

A ring counter is a type of digital counter circuit that is constructed using a shift register. It gets its name from the way it operates, where the data bits are circulated (or "ringed") through a sequence of flip-flops. This circular shifting behavior gives rise to its unique properties and applications.

## Working Principle of a Ring Counter

A ring counter typically consists of a set of flip-flops connected in a circular manner. Each flip-flop output is connected to the input of the next flip-flop in the sequence, and the output of the last flip-flop is fed back to the input of the first flip-flop, forming a closed loop. This configuration creates a cyclic shift of the data bits through the flip-flops.

When a clock signal is applied to the ring counter, the data bits are shifted from one flip-flop to the next with each clock cycle. As a result, the ring counter generates a sequence of binary states that repeat after a specific number of clock cycles, depending on the number of flip-flops in the circuit. The binary sequence generated by the ring counter can be used for various applications, such as sequencing, pattern generation, and control operations.

In the above table, the highlighted 1’s are pre-set 1. Pre-set 1 is generated when

• ORI input set to low, and that time the Clk doesn’t care.
• When the ORI input is set to high, and the low clock pulse signal is passed as the negative clock edge is triggered.

A ring forms when the pre-set 1 is shifted to the next flip-flop at each clock pulse.

## Types of Ring Counter in Digital Logic

There are two types of Ring Counter in Digital Logic.

1. Straight Ring Counter
The Straight Ring Counter is also known as the One Hot Counter. The result of the previous flip-flop is used as an input by the first flip-flop. The ORI input is passed to the PR input for the first flip flop and to the clear input for the remaining flip flops in the ring counter.

Note: The straight ring counter circulates the single 1 (or 0) bit around the ring.

### Truth Table

#### Signal Diagram

2. Twisted Ring Counter
A switch-tail ring counter is what the Twisted Ring Counter is called. The output of the last flip-flop is passed as an input to the first flip-flop, just like in a straight ring counter. The ORI input is used as the clear input by all of the flip flops in the twisted ring counter.

Note: The twisted ring counter circulates a stream of 1’s followed by 0 around the ring.

### Signal Diagram

Advantages of Ring Counter in Digital Logic

1. Simplicity: Ring counters are relatively simple to implement using standard flip-flop components, making them easy to design and integrate.

2. Compactness: The closed-loop structure of a ring counter enables it to generate sequences without complex external logic, making it space-efficient for integrated circuits.

3. Predictable Sequence: The cyclic behavior of the ring counter ensures a consistent and known sequence, which is beneficial in applications where predictability is essential.

## Uses of Ring Counter in Digital Logic

1. Sequencing: Commonly used in digital clocks, traffic light control systems, and industrial automation for generating orderly sequences.

2. Pattern Generation: Applied in LED displays, scrolling text displays, and sequential control systems to create specific patterns of outputs.

3. Decoding and Control: Serve as address decoders in memory devices and implement control logic in digital systems.

4. Frequency Division: Used as frequency dividers, where the output frequency is a fraction of the input clock frequency.

## Limitations of Ring Counter in Digital Logic

Despite their advantages, ring counters have limitations. Fixed sequence lengths and potential glitches during shifting are considerations designers must account for in their applications.

Conclusion
Ring counters are a fascinating and useful component in digital logic design, offering simplicity, predictability, and compactness in generating sequences of states. Their cyclic behavior and closed-loop structure make them versatile for various applications, from basic sequencing tasks to more complex control operations. By understanding the various types of ring counters and their characteristics, digital designers can choose the most suitable variant for their specific applications, contributing to more efficient and functional digital designs.

Here are some of the frequently asked questions about ring counter in Digital Logic.

Q1. What is a ring counter in digital logic?
A ring counter is a specialized type of digital counter circuit constructed using a series of flip flops interconnected in a circular manner. The data bits circulate through the flip flops, creating a cyclic sequence of binary states. This unique configuration has applications in sequencing, pattern generation, and control operations.

Q2. How does a ring counter work?
A ring counter operates by shifting data bits through a circular arrangement of flip flops. Each flip flop output is connected to the input of the next flip flop, forming a closed loop. When a clock signal is applied, the data bits move from one flip flop to the next in a cyclic manner, generating a repeating binary sequence.

Q3. What are the advantages of using ring counters?
Ring counters offer several advantages, including simplicity of design, compactness due to the closed loop structure, and the ability to generate predictable sequences. They are well suited for applications requiring repetitive sequences, such as digital clocks, LED displays, and control logic in various systems.

Q4. What are the different types of ring counters?
There are several types of ring counters:
Single Ring Counters: Basic unidirectional counters that generate a simple repeating sequence.
Johnson Counters: Create sequences with fewer repeated states using complemented outputs.
Walking Ring Counters: Shift sequences bidirectionally, resulting in longer and more intricate patterns.
Switch Tail Ring Counters: Allow for reversible pattern generation by controlling shifting direction.
Modulo N Counters: Generate sequences with a period of N clock cycles for precise timing applications.

Q5. Where are ring counters commonly used?
Ring counters find applications in various domains, including:
Sequencing: Used in digital clocks, traffic lights, and industrial automation for generating orderly sequences.
Pattern Generation: Employed in LED displays, scrolling text displays, and control systems for creating specific output patterns.
Decoding and Control: Serve as address decoders in memory devices and implement control logic in digital systems.
Frequency Division: Used as frequency dividers in communication systems and signal processing.