Asynchronous modulus counter

This post covers the Asynchronous modulus counter with the help of a set of frequently asked questions (FAQs) and answers.


What does it mean by the term modulus of a counter?

The modulus of a counter is the number of unique states through which the counter will sequence. The maximum possible number of states (maximum modulus) of a counter is 2n , where n is the number of flip-flops in the counter.

What do you mean by the term truncated binary counters?

Counters can be designed to have a number of states in their sequence that is less than the maximum of 2n , where n is the number of flip-flops required to design the counter. This type of sequence in the counter is called a truncated sequence and the counters are termed as truncated binary counters.

Give one example of a truncated binary counter.

One common example of a truncated binary counter is a Decade Counter with a truncated sequence of ten (called MOD 10) i.e. count sequence of zero (0000) through nine (1001).

What is a BCD decade counter?

A decade counter (called MOD 10) with a count sequence of zero (0000) through nine (1001) is a BCD decade counter because its ten-state sequence produces the BCD code.

Give one application area where the BCD decade counter is used?

BCD decade counter is useful in display applications in which BCD is required for conversion to a decimal readout.

How many flip-flops are required to implement a decade counter?

A decade counter requires four flip-flops (three flip-flops are insufficient because 2 3 = 8).

What is partial decoding used in designing of modulus counter?


Figure 1(a) Logic diagram of asynchronous decade counter showing the partial decoding of count ten(1010) with a NAND gate.

Notice in Figure 1(a) that only Q1 and Q3 are connected to the NAND gate inputs. This arrangement is an example of partial decoding, in which the two unique states (Q1 = 1 and Q3 = 1) are sufficient to decode the count of ten because none of the other states (zero through nine) have both Q1 and Q3 HIGH at the same time. When the counter goes into count ten (1010), the decoding gate output goes LOW and asynchronously resets (clear) all the flip-flops.

What is a glitch in truncated counters?

In a truncated sequence counter, the transitional states produce undesired voltage spikes of short duration (glitches) on the outputs of a decoder connected to the counter.

This unwanted spike of voltage is known as a glitch.

How many states will be there in a mod-6 counter?

There will be six states in a mod-6 counter. This means the counter goes through the counting sequence from 000 to 101 in each complete cycle before it recycles back to its starting state.

What do you mean by the term ‘MOD number’ of any counter?

The MOD number of any counter is generally equal to the number of states that the counter goes through in each complete cycle before it recycles back to its starting state.

A MOD-10 counter is known as a divide-by-10 counter –Why?

In a MOD-10 (decade) counter the signal output from the last FF (i.e., the MSB) will have a frequency of 1/10 the input clock frequency; so it is known as a divide-by-10 counter.

Related posts (for further study) on Binary Counter

Asynchronous Counter – study & revision notes

Synchronous Counter – Study & Revision Notes

How to design a Synchronous counter – step by step guide

2-bit Synchronous Binary Counter using J-K flip-flops

A 3-Bit Asynchronous Binary Counter – Up Counter

Asynchronous Up counter for Positive & Negative edge-triggered flip-flops

Binary Counter Sequential Circuit – FAQs

Frequently Asked Questions on Flip-Flops Sequential Circuit

Numerical problems on asynchronous counter & synchronous counter

J-K flip-flop – Frequently asked questions for semester & GATE exam

Modulus-M (MOD-M) asynchronous counter – Study and revision notes

Digital Electronics – Hub page

Author of this post

This post is co-authored by Professor Saraswati Saha, who is an assistant professor at RCCIIT, a renowned degree engineering college in India. Professor Saha teaches subjects related to digital electronics & microprocessors.

Asynchronous modulus counter
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