digitals

Question

Answer 1

Undertsand this truth table :

A	B	A'+B' .....Y(say)	B'	A Ex-Or B'	(A Ex-Or B')' .....X(say)	Y	X	Y'	X'	f1=X Ex-Or Y'	f2=(Y'+X')'
0	0	1	1	1	0	1	0	0	1	0	0
0	1	1	0	0	1	1	1	0	0	1	1
1	0	1	1	0	1	1	1	0	0	1	1
1	1	0	0	1	0	0	0	1	1	1	0

X represnts Sum output of Half adder of first level of gates.

F2 represents Subtract output of Half subtractor of second level of gates.

Hence half adder followed by half subtractor.

Comments

no......if we solve the output of X then we get A(EX-OR)B and the output of gate 1 i.e mentioned u in above is A'+B' which does not represent carry of half adder i.e. carry=AB

In 2nd level,the output of f1(gate 2 i.e mentioned u in above) is A+B which does not represent carry of substractor i.e. carry=A'B  and output of f2(gate 4 i.e mentioned u in above) is A(EX-OR)B

then how can we say this ckt represent half adder followed by half substractor.

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Yes.Only sum and difference outputs are correct. Borrow and carry are not correct thats whay I didn't mention about them, its bcoz the circuit is not designed properly.

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then op(c) also correct.