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Representing AND gate using NOR gate only:
              AND operation is achieved by passing complemented input through the NOR gate as shown in the logic circuit diagram
              given below.


                           A                    A'
                                      1                                       Output in NOR gate 1 is A'
                           A
                                                                 3     A.B    Output in NOR gate 2 is B'
                                                                              Output in NOR gate 3 is (A'+B')'

                           B                    B'                            = (A')'.('B')'    [De Morgan’s Law]
                                      2
                          B                                                   = A.B     [Involution Law]


              2.7.6 XOR Gate
              The XOR gate is a digital logical gate that produces 1 (high) as output for an odd number of 1 (high) as input. It is
              pronounced as exclusive OR gate. An encircled plus sign (⊕) is used to show the XOR operation.
              The symbol and truth table of the XOR gate are given below.

                                          A           B          A⊕B             A                  A⊕B

                                          0           0           0              B
                                          0           1           1                 Symbol of XOR gate
                                          1           0           1
                                          1           1           0          The Boolean expression  of a two
                                                                             variables XOR gate is A'.B+A.B'
                                     Truth table of two variables XOR gate


              The logic circuit diagram of the two variable XOR gate is as follows:

                                               A                A.B'

                                               B'
                                                                                A'.B + A.B'



                                              A'
                                                                A'.B
                                               B


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

                                    A         B          C       A⊕B⊕C
                                    0         0          0         0
                                    0         0          1         1
                                    0         1          0         1

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



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