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The truth table of the three variables XNOR gate, Boolean expression and logic circuit diagram are as follows:

                                            A          B         C        A⊙B⊙C
                                            0          0         0           1
                                            0          0         1           0
                                            0          1         0           0
                                            0          1         1           1
                                            1          0         0           0
                                            1          0         1           1          Boolean  expression  of the three
                                            1          1         0           1          variable XNOR gate is
                                            1          1         1           0          A'.B'.C' + A'.B.C + A.B'.C + A.B.C'.

                                  A'               A'.B'.C'
                                  B'
                                  C'


                                  A'             A'.B.C                    A'.B'.C' + A'.B.C + A.B'.C + A.B.C'
                                  B
                                  C


                                  A                A.B'.C
                                  B'
                                  C

                                  A                A.B.C'
                                  B
                                  C'

              Let us give  some more examples of drawing logic circuit from a Boolean expression and vice versa.
              Example 1: Draw the logic circuit diagram of the following Boolean expression A'.C + A.B'.
              The gates will be (A' AND C) OR (A AND B').
              Ans.
                    A'
                                    A'.C
                    C
                                                    A'.C + A.B'


                   A                A.B'

                   B'

              Example 2: Draw the logic circuit diagram of the following Boolean expression (A'+B'+C') + A.B.
              Ans. The gates will be (A NAND B NAND C) OR (A AND B) or (A' OR B' OR C') OR (A AND B).
              The one is drawn below:

                                       A                    A'+B'+C'
                                       B
                                       C
                                                                                    (A'+B'+C')+A.B


                                                            A.B





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