//四选一多路开关MUX4—1

module MUX4—1 (EN ,IN0 ,IN1 ,IN2 ,IN3 ,SEL ,OUT );

               input  EN ;                       //使能端

               input  [7:0] IN0 ,IN1 ,IN2 ,IN3 ;     //四输入

               input  [1:0] SEL ;                 //开关量

              output [7:0] OUT ;                 //一输出

               reg  [7:0] OUT ;

                always @(SEL  or EN  or IN0  or IN1  or IN2  or IN3 )

               begin

                               if (EN  == 0) OUT  = {8{1''b0}};

                               else

                                              case (SEL )

                                                             0 : OUT  = IN0 ;

                                                             1 : OUT  = IN1 ;

                                                             2 : OUT  = IN2 ;

                                                             3 : OUT  = IN3 ;

                                                             default : OUT  = {8{1''b0}};

                                              endcase

               end

endmodule