Assign Statement In Verilog
- You can use assign statement inside of module.
- You can use assign statement to output port and any wire declared inside the module
Examples of assign statement
In above example, y is output port and we are assigning this output port to a and b. It will create a and gate where a and b are inputs and y is output
In above example, we've descrived a NAND gate. We can use one statemetn but for better understanding we've use two statement to illustrate how we can use assign statement to both wire and output port. wire w is assign with a AND b, and output y is assigned not of wire w. This creates a NAND gate in verilog HDL.
In above example, we have described a full-adder using assign statement. Note that we can write complete boolean equation using assign statement
We can also use Verilog operators using assign statement. Below is the example of full-adder using assign statement and Verilog operator
In above example, we are using + operator, which addition operator in Verilog. We are assigning output sum and carry with addition of a, b and cin.
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Verilog Tutorial
Verilog code example, what is verilog .
Verilog is a hardware description language (HDL) that is used to describe digital systems and circuits in the form of code. It was developed by Gateway Design Automation in the mid-1980s and later acquired by Cadence Design Systems.
Verilog is widely used for design and verification of digital and mixed-signal systems, including both application-specific integrated circuits (ASICs) and field-programmable gate arrays (FPGAs). It supports a range of levels of abstraction, from structural to behavioral, and is used for both simulation-based design and synthesis-based design.
The language is used to describe digital circuits hierarchically, starting with the most basic elements such as logic gates and flip-flops and building up to more complex functional blocks and systems. It also supports a range of modeling techniques, including gate-level, RTL-level, and behavioral-level modeling.
What was used before Verilog ?
Before the development of Verilog, the primary hardware description language (HDL) used for digital circuit design and verification was VHDL (VHSIC Hardware Description Language). VHDL was developed in the 1980s by the U.S. Department of Defense as part of the Very High-Speed Integrated Circuit (VHSIC) program to design and test high-speed digital circuits.
VHDL is a complex language that enables designers to describe digital systems using a range of abstraction levels, from the low-level transistor and gate levels up to complex hierarchical systems. It was designed to be more descriptive and flexible than earlier HDLs, such as ABEL (Advanced Boolean Expression Language), ISP (Integrated System Synthesis Procedure), and CUPL (Compiler for Universal Programmable Logic).
Despite the development of Verilog and its increasing popularity since the 1980s, VHDL remains a widely used HDL, particularly in Europe and in the military and aerospace industries. Today, both Verilog and VHDL are widely used in digital circuit design and verification, with many companies and organizations using a combination of the two languages.
Why is Verilog better than its predecessor languages ?
Verilog introduced several important improvements over its predecessor languages, which helped make it a more popular and effective HDL for digital circuit design and verification. Here are a few reasons why Verilog is considered better than its predecessor HDLs:
How is Verilog useful ?
Verilog creates a level of abstraction that helps hide away the details of its implementation and technology.
For example, the design of a D flip-flop would require the knowledge of how the transistors need to be arranged to achieve a positive-edge triggered FF and what the rise, fall and clk-Q times required to latch the value onto a flop among many other technology oriented details. Power dissipation, timing and the ability to drive nets and other flops would also require a more thorough understanding of the physical characteristics of a transistor.
Verilog helps us to focus on the behavior and leave the rest to be sorted out later.
The following Verilog code describes the behavior of a counter. The counter counts up if the up_down signal is 1, and down if its value is 0. It also resets the counter if the signal rstn becomes 0, making it an active-low reset.
The simple example shown above illustrates how all the physical implementation details (interconnection of underlying logic gates like NAND and NOR) have been hidden while still providing a clear idea of how the counter functions.
ctr is a module that represents an up/down counter, and it is possible to choose the actual physical implementation of the design from a wide variety of different styles of flops optimized for area, power and performance. They are usually compiled into libraries and will be available for us to select within EDA tools at a later stage in the design process.
How is Verilog different from software languages like C and Java ?
Verilog is a hardware description language (HDL) used to describe digital circuits and systems, while C and Java are software programming languages used to write code that runs on general-purpose computers. Here are some of the main differences between Verilog and programming languages like C and Java:
Overall, Verilog is a specialized language designed specifically for digital circuit design and isn't used for general-purpose programming like C and Java. While there are some similarities in syntax and programming concepts between these languages, the primary focus and application of Verilog is on the design, simulation, and implementation of digital circuits and systems.
What may replace Verilog in the future ?
It's difficult to predict exactly what may replace Verilog in the future, but there are several emerging technologies and languages that may have an impact on the future of digital system design and verification.
One technology that may affect the future of digital system design is High-Level Synthesis (HLS), which is a technique for automatically generating hardware designs from high-level descriptions in languages like C, C++, and SystemC. HLS allows designers to express their design intents and functionality at a higher level of abstraction, rather than specifying the details of logic gates and register transfers in Verilog or VHDL. This could enable more efficient and rapid design of digital systems, and allow designers to explore more design space in a shorter period of time.
Another technology that may impact the future of digital system design is machine learning and artificial intelligence (AI), which have the potential to significantly streamline the design and verification process of digital systems. For example, machine learning algorithms can be used to automatically optimize and generate hardware designs, reducing the need for manual design efforts.
There are also emerging HDLs that are trying to address some of the limitations of Verilog and VHDL, such as Chisel and MyHDL, which are based on more modern programming concepts and provide higher-level abstractions.
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Note that you can also assign an initial value to a reg when you declare it, like this: output reg icache_ram_rw = 1'b0; This will ensure it starts with the zero value in simulation. For synthesis, your results will depend on the synthesis tool and target technology (for FPGAs, you can generally assign an initial value for hardware; for ASIC ...
I searched the web for an answer and tried all kinds of things but still cannot get the output assigned. Here's the code: input CLK, input En, input CLR, input [7:0] in, output [7:0] out. ); reg[7:0] temp;
Verilog assign statement. Signals of type wire or a similar wire like data type requires the continuous assignment of a value. For example, consider an electrical wire used to connect pieces on a breadboard. As long as the +5V battery is applied to one end of the wire, the component connected to the other end of the wire will get the required ...
A Wire will create a wire output which can only be assigned any input by using assign statement as assign statement creates a port/pin connection and wire can be joined to the port/pin. A reg will create a register (D FLIP FLOP ) which gets or recieve inputs on basis of sensitivity list either it can be clock (rising or falling ) or ...
The only real difference between wire and reg declarations in Verilog is that a reg can be assigned to in a procedural block (a block beginning with always or initial), and a wire can be assigned in a continuous assignment (an assign statement) or as an output of an instantiated submodule.. You simply need to declare each net as wire or reg depending on how you will assign it a value.
You can only have one source driving a given net, so having result being assigned in multiple places won't work (for synthesis at least). Furthermore the output a module cannot be connected directly to a reg type variable. Instead, to connect multiple things together in Verilog, you use wire (net data type).. For example
The LHS of an assign statement cannot be a bit-select, part-select or an array reference but can be a variable or a concatenation of variables. reg q; initial begin assign q = 0; #10 deassign q; end force release. These are similar to the assign - deassign statements but can also be applied to nets and variables. The LHS can be a bit-select of ...
The verilog assign statement is typically used to continuously drive a signal of wire datatype and gets synthesized as combinational logic. Here are some more design examples using the assign statement.. Example #1 : Simple combinational logic. The code shown below implements a simple digital combinational logic which has an output wire z that is driven continuously with an assign statement to ...
In Verilog we design modules, one of which will be identified as our top-level module. Modules usually have named, directional ports (specified as input, output or inout) which are used to communicate with the module. In this example the module's behavior is specified using Verilog's built-in Boolean modules: not, buf, and, nand, or, nor, xor,
Assign Statement In Verilog. assign keyword is used to assign ouput port or wire some digital logic. This keyword is the part of dataflow modeling in Verilog. In this post, we will see how to use this keyword in your Verilog code. You can use assign statement inside of module. You can use assign statement to output port and any wire declared ...
An always block as far as Verilog is concerned is executed line by line, which means anything that is assigned within the always block must be able to store a value temporarily during the execution of the block, and depending on the code after execution as well.
Verilog HDL: The First Example Module, I/O Ports, Bus, and Assign A Verilog module of a circuit encapsulates a description of its functionality as a structural or behavioral view of its input-output relationship. A structural view could be as simple as a netlist of gates or as complex as a high level architectural partition of the circuit into major functional blocks, such as an arithmetic and ...
Multi-bit Nets I We can declare signals that are more than 1 bit wide in Verilog I Use the syntax [MSB bit index : LSB bit index] before a signal name to declare its bit-width I When connecting multi-bit inputs or outputs to another module, the bit-widths of the signals need to match! module two_bit_adder (input [1:0] x, input [1:0] y, output [2:0] sum);
Verilog -- how to assign mux/selector output to module's output. 0. Verilog latch occurring with instantiating modules with in a generate statement. 0. What to do with GND of differential mode signals? 0. Assigning a declared wire to connect ports on two different Verilog modules. 1.
Here my 2cents, wire [32-1:0] DATA;//bidireccional port in VERILOG/VHDL. logic put_input_in_bidi; assign m_sram_if.SRAM_DATA_READ = DATA;//read from inout port.
Verilog is a hardware description language (HDL) that is used to describe digital systems and circuits in the form of code. It was developed by Gateway Design Automation in the mid-1980s and later acquired by Cadence Design Systems. Verilog is widely used for design and verification of digital and mixed-signal systems, including both ...
If the signal is driven by assignments in a procedural block (a block beginning with always or initial ), then it must be declared as reg. If the signal is driven by continuous assignment (an assign statement) or is the output of a module instance, then it must be declared as wire (or one of its variants like wor or wand ), or as an output ...
1. In Verilog, input arguments to a task are copied by value upon entry to the task, and output arguments get copied upon exit to the task. Nothing gets transferred through the arguments while the task consumes time. SystemVerilog adds a ref argument direction which means the argument gets passed as a reference.
I have a 128-bit input that I am trying to assign to four different 32-bit registers. I believe the issue is the way I have the 128-bit input coded in my test bench because my output is just a 128-bit string of zeros.
@Raviraj Verilog-1995, Verilog-2001 and Verilo-2005 do not support Array style ports, The syntax was added in 2009 and from on then is known as SystemVerilog. This is not the same as the per-2009 SystemVerilog which was a verification add-on to Verilog. Today they are the same thing.