Decade Counter | Counter Circuit Basics

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A decade counter is very common in today’s electronics. Most commonly available as IC CD7490, contains multiple flip flops to convert BCD-to-decimal and is incorporated as part of larger integrated circuits.

A decade counter counts in a sequence of ten and then returns back to zero after the count of nine.

Decade Counter Circuit Diagram

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Basically, counters can be implemented quite easily using register type circuits. Besides decade counter, there are various others that are also used regularly. Let’s take a look.

Asynchronous counter

An asynchronous counter is a simple D-Flip flop, with the output fed back as input. The output changes state for each clock input. This creates a circuit that can store one bit of information. This counter will increment once for every clock cycle and takes two clock cycles for a transition from 0 to 1 and a transition from 1 to 0 creating a new clock with a 50% duty cycle.

Synchronous counter

The clock inputs of all the flip-flops are connected together and are triggered by the input pulses.  Thus, all the flip-flops change state simultaneously. An advantage of synchronous counters is that there is no cumulative time delay because all flip-flops are triggered in parallel.

Ring counter

A ring counter is a shift register with the output of one flip flop connected to the input of the next in a ring. Typically, a pattern consisting of a single bit is circulated so the state repeats every n clock cycles if n flip-flops are used. It is initiated such that only one of its flip-flops is the state one while others are in their zero states

Johnson Counter

A Johnson counter is a kind of modified ring counter, where the output of the last stage is inverted before being fed back into the first flop. The register cycles through a sequence of bit-patterns, whose length is equal to twice the length of the shift register, continuing indefinitely. It is very commonly found in digital-to-analog converters.

Decade Counter

The basic decade counter is an electronic circuit with a 4-bit binary output and an input signal (called a clock). With each clock pulse the outputs advance to the next higher value, resetting to 0000 when the output is 1001 and a subsequent clock pulse is received. Decade counters are used in clock circuits, frequency dividers, state machines, and sequencers, just to name a few applications.

Decade Counter/Divider with Ten Decoded Outputs Datasheet: click here

For more detailed lesson on counters, have a look at the presentation below;

This article was first published on 26 August 2017 and was updated on 19 November 2020.

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