Topic: Digital Electronics
What will be the output of the following circuit, if point-P is stuck at 1?
(The circuit shows A and B feeding an OR gate. B is inverted and fed with C into an AND gate. The outputs of these two gates feed an OR gate to produce intermediate signal x. Then x and P feed an XOR gate to produce Y.)
- A. $A+B+C$
- B. $A^{\prime} B^{\prime} C^{\prime}$
- C. $(ABC)^{\prime}$
- D. 0
Answer: B. $A^{\prime} B^{\prime} C^{\prime}$
Explanation: From the logic diagram, the intermediate signal $x = (A+B) + \bar{B}C = A + B + \bar{B}C = A+B+C$.
Since point P is stuck at 1, the input $C_{XOR}=1$. When any input of an XOR gate is 1, it behaves as an inverter.
Thus, $Y = x \oplus 1 = \bar{x} = \overline{A+B+C} = \bar{A}\bar{B}\bar{C}$ (or $A' B' C'$).