Blocking / Non-Blocking Assignments in Verilog

   Blocking vs. Non-Blocking Assignment


  A Blocking Statement must executed before the execution of statements that follow it in a sequential block.It can be used in Procedural assignments like initial,always and continious statements like assign statements.It is recommended to use within combinattional always block.it is represented by "=" operator sign


           Example : 
                         module block();
                              integer a,b,c,d;


                       // Blocking Assignments       


                           initial
                              begin
                                a = 5; b = 3;
                                #15 c = 8;
                                #20 d = 15;
                             end
                        endmodule




In Above Example ,
                    At time '0'  a and b have the value 5 and 3 respectively
                    At time '15' c have the value 8 and
                    At time '35' d have the value 15




  A Non Blocking Statement first evaluate the value and then assigns it in the next event change,just the ways sequential circuits work.They always the sample the value of rising/falling edge of clock.It can be used in the procedural blocks like initial and always. assign statement is not permitted .It is recommended to use within sequential always block .It is represented by "<=" operator sign


        
         Example : 
                         module non_block();
                              integer a,b,c,d;


                       // Non-Blocking Assignments       


                           initial
                              begin
                                      a <= 5;
                                #10 b <= 3;
                                #15 c <= 8;
                                #20 d <= 15;
                             end
                        endmodule


  In Above Example ,
                          At time '0'   a have the value 5 .
                          At time '10' b have the value 3.
                          At time '15' c have the value 8  and 
                          At time '20' d have the value 15