Question

Fig. shows a logic commbination with P, Q, R, S are inputs. When P, Q, R and S all are 1; the outputs X, Y and Z are 1, 1 and 0 respectively. When input P and R are changed to state 0 with inputs Q and S still in state 1; the output X, Y, Z change to

(1) X = 1; Y = 0; Z = 0

(2) X = 1; Y = 1; Z = 1

(3) X = 0; Y = 1; Z = 0

(4) X = 0; Y = 0; Z = 1

Answer 1

(3) X = 0; Y = 1; Z = 0

P and Q are inputs of a AND gate. When P = 0; Q = 1; X = 0. R and S are inputs of a NOR gate and its output is input of a NOT gate. Obvisouly with R = 0 and S = 1; the output of NOR gate is 0. This is input of NOT gate. Therefore Y = 1. Now X = 0 and Y = 1 are inputs of a NOR gate; the output Z = 0. This is correctly representation in (3).