UGCNET-Dec2012-II: 1

Question

Consider the circuit shown below. IN a certain steady state, ‘Y’ is at logical ‘l’. What are the possible values of A, B, C?

• A. A=0, B=0, C=1
• B. A=0, B=C=1
• C. A=1, B=C=0
• D. A= B=1, C=1

Comments

where is the ckt?

Answer 1

assuming f as Y in order to  y=1 (steady) state the last AND gate must have both input as 1

so   C=1 (so choice C is out) and for other input to be 1  either B=0 (which ensures output of 2nd NAND gate as 1)  

or A=1 as it ensure the output of second  NAND gate as 0 if other input is also 1 , now which is f which may be 0 or 1 so to be safe side leave this

i.e         B=0  and  A=1 or  0     C=1    choice A)satisfy and also choice D)

hence ans should be A and also D

Comments

What about option D ?

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D is also correct

Answer 2

option A &D staisfy the conditions