ISRO2015-4

Question

A modulus -$12$ ring counter requires a minimum of

• A. $10$ flip-flops
• B. $12$ flip-flops
• C. $8$ flip-flops
• D. $6$ flip-flops

Comments

• A ring counter is a circular shift register with only one flip-flop being set at any particular time; all others are cleared.
• A $k$ - bit ring counter circulates a single bit among the flip flops to provide $k$ distinguishable states.

 

Answer 1

12 flip flops required.
In ring counter, n flip flops generate n states where in twisted ring counter n flip flops generate 2n states.
for more info
http://www.electronics-tutorials.ws/sequential/seq_6.html

Comments

Answer is b) 12 flip-flops

The “MODULO” or “MODULUS” of a counter is the number of states the counter counts or sequences through before repeating itself and a ring counter can be made to output any modulo number.

A “mod-n” ring counter will require “n” number of flip-flops connected together to circulate a single data bit providing “n” different output states.

For example, a mod-8 ring counter requires eight flip-flops and a mod-16 ring counter would require sixteen flip-flops.

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Answer 2

Answer- 12 flip flop

Answer 3

For any counter:-

1. There are a certain number of Flip Flops from which it is built.
2. There are a certain number of states that the counter can be in. Each state represents a unique value.

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Synchronous Counters:

$n$ Flip Flops count $2^n$ different values.

Or you can say that $n$ Flip Flops result in $2^n$ states, and each state represents a distinguishable value.

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Asynchronous Counters (aka Ripple Counters):

$n$ Flip Flops count $2^n$ different values.

Or you can say that $n$ Flip Flops result in $2^n$ states, and each state represents a distinguishable value.

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Johnson Counter: (aka Twisted Ring Counter, Switch-Tail Ring Counter)

$n$ Flip Flops count $2n$ different values.

Or you can say that $n$ Flip Flops result in $2n$ states, and each state represents a distinguishable value.

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Ring Counters:

$n$ Flip Flops count $n$ different values.

Or you can say that $n$ Flip Flops result in $n$ states, and each state represents a distinguishable value.

 

Now unless explicitly mentioned otherwise, a ring counter should be assumed as a straight ring counter, which leads us to Option B