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Question

https://gateoverflow.in/17235/gate1993-6-2

Explanation is not provided in the answer. Can anyone please give explanation for the answer.

Answer 1

According to the diagram showed in the answer section, question is asking what should be the input such that next output will be same as current output. We call it latch mode. We can clearly see from diagram there are two self loops of 1 on A and 1 on B. So to get a stable output we need 1 on A and 1 on B. hence it can be given by a OR b i.e a+b.

Comments

if a=0 and b=1 why it won't be in a stable state?

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There is only one input not a AND b simultaneously. Either you can give a or b at a time.

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if a=0 and b=1 why it won't be in a stable state?

Even this statement of yours is true as it will give us stable output at S2(out 2). Only the case when it will fluctuate between out 1 and out 2 is when both will be 0. Relate it to TOC.

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Thanks got it.