Verilog HDL Examples - Blocking V/S Non Blocking Assignment (Hardware Realization) Part#1

In the article, we will be doing Verilog HDL Coding for a simple D Flip Flop using Blocking and Non Blocking Assignments and will see how this HDL will get realize into the real D Flip Flop Circuit/Hardware.

Here, the goal is to understand the correct use of Blocking and Non Blocking assignment statements in Verilog HDL.

Believe me , this article series outcomes are going to be very interesting. This is part one of Blocking V/S Non Blocking Assignment Experiment.

Lets Start !!!

Here, is the Verilog HDL code for a simple D Flip Flop using Non Blocking Assignment Statements in the Procedural Block(Note: 'always' and 'initial' are called procedural block in Verilog HDL)


//#############D FF Verilog HDL Code with Non Blocking Assignments##################

// Code your design here

module dff(

input clk,

input rst,

input d,

output q0

);

always @(posedge clk)

begin

if(!rst)

begin

q0 <= 1'b0;

end

else

begin

q0 <= d;

end

end

endmodule


Now, Lets see how this HDL code gets realize to the hardware using Yosys Synthesis Tool.

Yosus Synthesis Diagram:


As you can see in the above diagram, the HDL code gets realized correctly into one MUX (Because of if/else condition) and one D Flip Flop as expected.


Now, Lets replace all Non- Blocking assignments into Blocking assignments in the Verilog HDL code and observe the new realized hardware by synthesis tool again.


//############ D FF Verilog HDL Code with Blocking Assignments########

// Code your design here

module dff(

input clk,

input rst,

input d,

output q0
);

always @(posedge clk)

begin

if(!rst)

begin

q0 = 1'b0;

end

else

begin

q0 = d;

end

end

endmodule


Yosys Synthesis Diagram:






As you can see in the above both diagrams, there is no difference ( They both are exactly identical).


Observations:

1) Realization of a single D Flip Flop results exactly same with Blocking as well as Non -Blocking Signal Assignments.

2) Now, are these Blocking and Non Blocking Assignments are interchangeable ? Is there any difference in using these both?

Lets discuss more on Blocking V/S Non Blocking Assignments in Part#2 of this Article Series.

Thanks You !!!