Verilog Assignments

Variable declaration assignment, net declaration assignment, assign deassign, force release.

  • Procedural continuous

Legal LHS values

An assignment has two parts - right-hand side (RHS) and left-hand side (LHS) with an equal symbol (=) or a less than-equal symbol (<=) in between.

The RHS can contain any expression that evaluates to a final value while the LHS indicates a net or a variable to which the value in RHS is being assigned.

Procedural Assignment

Procedural assignments occur within procedures such as always , initial , task and functions and are used to place values onto variables. The variable will hold the value until the next assignment to the same variable.

The value will be placed onto the variable when the simulation executes this statement at some point during simulation time. This can be controlled and modified the way we want by the use of control flow statements such as if-else-if , case statement and looping mechanisms.

An initial value can be placed onto a variable at the time of its declaration as shown next. The assignment does not have a duration and holds the value until the next assignment to the same variable happens. Note that variable declaration assignments to an array are not allowed.

If the variable is initialized during declaration and at time 0 in an initial block as shown below, the order of evaluation is not guaranteed, and hence can have either 8'h05 or 8'hee.

Procedural blocks and assignments will be covered in more detail in a later section.

Continuous Assignment

This is used to assign values onto scalar and vector nets and happens whenever there is a change in the RHS. It provides a way to model combinational logic without specifying an interconnection of gates and makes it easier to drive the net with logical expressions.

Whenever b or c changes its value, then the whole expression in RHS will be evaluated and a will be updated with the new value.

This allows us to place a continuous assignment on the same statement that declares the net. Note that because a net can be declared only once, only one declaration assignment is possible for a net.

Procedural Continuous Assignment

  • assign ... deassign
  • force ... release

This will override all procedural assignments to a variable and is deactivated by using the same signal with deassign . The value of the variable will remain same until the variable gets a new value through a procedural or procedural continuous assignment. 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.

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 a net, part-select of a net, variable or a net but cannot be the reference to an array and bit/part select of a variable. The force statment will override all other assignments made to the variable until it is released using the release keyword.

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  • The Verilog-AMS Language

Ports, also referred to as pins or terminals, are used when wiring the module to other modules. As such, ports are wires. Ports declarations for simple wire are wire declarations with the keyword wire replaced by one of the following direction specifiers: input , output , or inout . For example:

For other types of wires, or for registers (registers may only be declared as outputs), the declaration is simply preceded by the direction specifier:

By default the content of multi-bit ports are interpreted as unsigned numbers (the values are interpreted as positive binary numbers). It is possible to explicitly specify whether the number is to be interpreted as a signed or unsigned number as follows:

In this case, gain is unsigned and offset is signed, which means it is interpreted as a twos-complement signed number. So, if gain = 4’bF, its value is interpreted as 15, and if offset = 7’b7FF, then its value is interpreted as -1.

If it is necessary to apply a discipline to a port, the port declaration should be repeated with direction specifier replaced by the discipline. For example:

Verilog also supports buses of continuous signals and wreals (you must declare these as buses rather than arrays):

The Cadence simulator does not seem to follow the standard when it comes to declaring buses of wreals. With the Cadence simulator you should declare buses of wreals as arrays rather than as buses:

  • Verilog Ports

01 Sep 2021

While declaring a Verilog module, port list needs to be also declared if we want our module to connect with another modules. The port list consists of various nets and variables, along with the direction.

Components of port

Each port consists of 3 main components:

  • Port direction
  • Port data type
  • Port signal name

Port Direction

There are 3 directions which can be used in the port list:

  • Input – This is used for the input ports and input is the keyword used to make an input port.
  • Output – This is used for output port.
  • InOut – This is used if the port is bidirectional, i.e., it can act as both input and output. inout is the keyword used for this.

Port Data type

Not all data types can be used as a port . Some of the data types like, real , event cannot be used with the port. Ports can be made signed or unsigned using signed keyword before the data type.

In the above example, the port declaration for a and b is invalid.

Port name can be any valid identifier in Verilog.

Port List Declaration

There are 2 ways in which port list can be declared.

Method One (Verilog 1996)

This method is more popular in old versions of Verilog, but in newer versions Verilog introduced a new way to declare a port list based on ANSCI C style. But the old way of declaration is still supported in recent versions and thus can also be used.

In this method, only the port name is used in the port list. The data type and the direction of the ports can be declared later in the body of the module. Also, in this method, the input ports cannot be declared as reg , it can only have a net data type.

Method two (Verilog 2001)

This method is based on ANSCI C, i.e., the way in which we declare the function arguments in C language. In this method, the port direction and data types are mentioned with the port name. If the direction and data type is not mentioned, the direction and data type of previous port is used for this port also. The ports declared using this method, cannot be redeclared in the module body.

Keys points to remember while declaring Verilog port list:

  • input ports can only have net data type.
  • In newer ANSCI C style port list declaration ports cannot be redeclared again inside module.
  • New and old style of port declaration cannot be mixed
  • Default data type of any port is net .

Referencing ports (Port Connection)

When we instantiate, a module having ports, we need to connect it to other modules or the top modules using the ports. There are 2 ways to connect the ports with the signals:

Port connection by Order

  • Port connection by name

In this connection, the signals which is declared inside the parent module should match the ports according to the position of the port in port list. This type of connection is prone to error, as signal can be easily connected to the wrong port.

Port connection by Name

In this connection, the name of the ports is used to connect the signal with the specific port. This type of connection is not prone to error as order of the ports are important in this case. .port_name(signal_name) is the syntax to use port connection by name.

  • Introduction to Verilog
  • Verilog Event Semantics
  • Basics of Verilog
  • Verilog Syntax
  • Data Types in Verilog
  • Verilog Vectors
  • Verilog Arrays
  • Verilog Modules
  • Verilog Operators
  • Verilog Procedural Blocks
  • Verilog Assignments
  • Different types of loops in Verilog
  • Conditional Statements in Verilog
  • Verilog functions and tasks
  • Compiler Directives in Verilog
  • Verilog System Functions
  • Delays in Verilog

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Modules and Ports in Verilog

A Module is a basic building design block in Verilog and it can be an element that implements necessary functionality. It can also be a collection of lower-level design blocks. As a part of defining a module, it has a module name, port interface, and parameters (optional). The port interface i.e. inputs and outputs is used to connect the high-level module with the lower one and hides internal implementation. 

Declaration

The module is declared using a keyword ‘module’ with an optional port list and followed by its implementation. In the end, it is enclosed with the keyword ‘endmodule’.

A module consists of variable declaration, dataflow statements, behavioral blocks, instantiation of lower hierarchical modules, tasks, and functions. All of these are optional depending on the requirement statements or blocks that can be used, but module, endmodule, and module name are mandatory. It is not allowed to have nested modules; instead, it allows instantiating sub-module to have the module connections.

An interface to communicate with other modules or a testbench environment is called a port. In simple words, the input/ output pins of digital design are known as ports. This interface is termed a port interface or port list. Since the port list is available for connection, internal design implementation can be hidden from other modules or an environment.

Verilog keywords used for port declaration are as follows:

Verilog ports

Ports in Verilog

  • Ports are of wire data type by default.
  • If output ports hold their value, then they must be declared as reg data type.
  • The input and inout ports can not be reg as they can not store values. Input ports pass signals from externally connected signals.

Connection rules in Verilog port

While writing a module, the designer needs to make sure what type of signals have to be connected to the module’s inputs and outputs and follow the below rules.

For understanding port connecting rules, consider the current design module as an internal world and outside of the module to be an external world.

Module instantiation

While designing complex digital circuits, usually it is split into various modules that connect to have a top-level block. Thus, Verilog supports a hierarchical design methodology. When a module is instantiated, a unique object is created and it has a unique name. Similarly, a top-level design can also be instantiated while creating a testbench.

 Following the hierarchical approach, a particular signal can be reached out following hierarchy and each identifier is separated using a dot.

A mechanism for connecting the port to the external signals

When a module is instantiated in the top-level hierarchy or top-level design in a testbench, any one of the following methods can be used.

Method A: Connecting a port list in an ordered manner

An ordered manner connection is feasible when a port list has minimum signals as the user has to follow the same order in which design level signals are declared.

Design declaration:

Design instantiation in testbench:

Observe that the port list in design mux_2_1 and its instantiation in testbench mux_tb follow the same order.

Note: It is not mandatory to use different names at the design and testbench level.

Method B: Connecting a port list by name

For complex designs having more ports, remembering and writing in the same order while instantiating the design is error-prone. In this method, the order of port list connection does not matter based on the port name, the connection is established.

For an above example,

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Verilog reg, Verilog wire, SystemVerilog logic. What’s the difference?

The difference between Verilog reg and Verilog wire frequently confuses many programmers just starting with the language (certainly confused me!). As a beginner, I was told to follow these guidelines, which seemed to generally work:

  • Use Verilog reg for left hand side (LHS) of signals assigned inside in always blocks
  • Use Verilog wire for LHS of signals assigned outside always blocks

Then when I adopted SystemVerilog for writing RTL designs, I was told everything can now be “type logic”. That again generally worked, but every now and then I would run into a cryptic error message about variables, nets, and assignment.

So I decided to find out exactly how these data types worked to write this article. I dug into the language reference manual, searched for the now-defunct Verilog-2005 standard document, and got into a bit of history lesson. Read on for my discovery of the differences between Verilog reg , Verilog wire , and SystemVerilog logic .

Verilog data types, Verilog reg, Verilog wire

Verilog data types are divided into two main groups: nets and variables. The distinction comes from how they are intended to represent different hardware structures.

A net data type represents a physical connection between structural entities (think a plain wire), such as between gates or between modules. It does not store any value. Its value is derived from what is being driven from its driver(s). Verilog wire is probably the most common net data type, although there are many other net data types such as tri , wand , supply0 .

A variable data type generally represents a piece of storage. It holds a value assigned to it until the next assignment. Verilog reg is probably the most common variable data type. Verilog reg is generally used to model hardware registers (although it can also represent combinatorial logic, like inside an always@(*) block). Other variable data types include integer , time , real , realtime .

Almost all Verilog data types are 4-state, which means they can take on 4 values:

  • 0 represents a logic zero, or a false condition
  • 1 represents a logic one, or a true condition
  • X represents an unknown logic value
  • Z represents a high-impedance state

Verilog rule of thumb 1 : use Verilog  reg  when you want to represent a piece of storage, and use Verilog  wire  when you want to represent a physical connection.

Assigning values to Verilog reg, Verilog wire

Verilog net data types can only be assigned values by continuous assignments. This means using constructs like continuous assignment statement ( assign statement), or drive it from an output port. A continuous assignment drives a net similar to how a gate drives a net. The expression on the right hand side can be thought of as a combinatorial circuit that drives the net continuously.

Verilog variable data types can only be assigned values using procedural assignments. This means inside an always block, an initial block, a task , a function . The assignment occurs on some kind of trigger (like the posedge of a clock), after which the variable retains its value until the next assignment (at the next trigger). This makes variables ideal for modeling storage elements like flip-flops.

Verilog rule of thmb 2 : drive a Verilog  wire  with  assign  statement or port output, and drive a Verilog  reg  from an  always  block. If you want to drive a physical connection with combinatorial logic inside an  always@(*)  block, then you have to declare the physical connection as Verilog  reg .

SystemVerilog logic, data types, and data objects

SystemVerilog introduces a new 2-state data type—where only logic 0 and logic 1 are allowed, not X or Z—for testbench modeling. To distinguish the old Verilog 4-state behaviour, a new SystemVerilog logic data type is added to describe a generic 4-state data type.

What used to be data types in Verilog, like wire , reg , wand , are now called data objects in SystemVerilog. Wire , reg , wand (and almost all previous Verilog data types) are 4-state data objects. Bit , byte , shortint , int , longint are the new SystemVerilog 2-state data objects.

There are still the two main groups of data objects: nets and variables. All the Verilog data types (now data objects) that we are familiar with, since they are 4-state, should now properly also contain the SystemVerilog logic keyword.

There is a new way to declare variables, beginning with the keyword var . If the data type (2-state or 4-state) is not specified, then it is implicitly declared as logic . Below are some variable declaration examples. Although some don’t seem to be fully supported by tools.

Don’t worry too much about the var keyword. It was added for language preciseness (it’s what happens as a language evolves and language gurus strive to maintain backward-compatibility), and you’ll likely not see it in an RTL design.

I’m confused… Just tell me how I should use SystemVerilog logic!

After all that technical specification gobbledygook, I have good news if you’re using SystemVerilog for RTL design. For everyday usage in RTL design, you can pretty much forget all of that!

The SystemVerilog logic keyword standalone will declare a variable, but the rules have been rewritten such that you can pretty much use a variable everywhere in RTL design. Hence, you see in my example code from other articles, I use SystemVerilog logic to declare variables and ports.

When you use SystemVerilog logic standalone this way, there is another advantage of improved checking for unintended multiple drivers. Multiple assignments, or mixing continuous and procedural ( always block) assignments, to a SystemVerilog variable is an error, which means you will most likely see a compile time error. Mixing and multiple assignments is allowed for a net. So if you really want a multiply-driven net you will need to declare it a wire .

In Verilog it was legal to have an assignment to a module output port (declared as Verilog wire or Verilog reg ) from outside the module, or to have an assignment inside the module to a net declared as an input port. Both of these are frequently unintended wiring mistakes, causing contention. With SystemVerilog, an output port declared as SystemVerilog logic variable prohibits multiple drivers, and an assignment to an input port declared as SystemVerilog logic variable is also illegal. So if you make this kind of wiring mistake, you will likely again get a compile time error.

SystemVerilog rule of thumb 1 : if using SystemVerilog for RTL design, use SystemVerilog  logic  to declare:

  • All point-to-point nets. If you specifically need a multi-driver net, then use one of the traditional net types like  wire
  • All variables (logic driven by  always  blocks)
  • All input ports
  • All output ports

If you follow this rule, you can pretty much forget about the differences between Verilog reg and Verilog wire ! (well, most of the time)

When I first wondered why it was possible to always write RTL using SystemVerilog logic keyword, I never expected it to become a major undertaking that involved reading and interpreting two different specifications, understanding complex language rules, and figuring out their nuances. At least I can say that the recommendations are easy to remember.

I hope this article gives you a good summary of Verilog reg , Verilog wire , SystemVerilog logic , their history, and a useful set of recommendations for RTL coding. I do not claim to be a Verilog or SystemVerilog language expert, so please do correct me if you felt I misinterpreted anything in the specifications.

  • Synthesizing SystemVerilog : Busting the Myth that SystemVerilog is only for Verification
  • 1800-2012 – IEEE Standard for SystemVerilog–Unified Hardware Design, Specification, and Verification Language
  • 1364-2005 – IEEE Standard for Verilog Hardware Description Language
  • A lively discussion in Google Groups on SystemVerilog var keyword

Sample Source Code

The accompanying source code for this article is a SystemVerilog design and testbench toy example that demonstrates the difference between using Verilog reg, Verilog wire, and SystemVerilog logic to code design modules. Download the code to see how it works!

[lab_subscriber_download_form download_id=8].

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16 thoughts on “Verilog reg, Verilog wire, SystemVerilog logic. What’s the difference?”

Good article. However, there is one significant gotcha that users need to be aware of. When converting RTL from wire/reg to logic, if you were using a net declaration assignment for a wire, that will not work with logic! As a variable type, assigning a value to a logic variable as part of the declaration merely initializes it to that value. No continuous assignment is inferred.

This is the only case where logic has not been a drop-in replacement for me in RTL.

Example: wire mysignal0 = A & B; // continuous assignment, AND gate logic mysignal1 = A &B; // not synthesizable, initializes mysignal1 to the value of A & B at time 0 and then makes no further changes to it. logic mysignal2; assign mysignal2 = A & B; // Continuous assignment, AND gate

Thanks for pointing that out Evan! I looked through the assignment section of the LRM and you’re correct. Like you said, the particular form of assignment in the first row of your example code is called net declaration assignment (section 10.3.1 of SV-2012 LRM), and as the name suggests it only works on nets. The second line in your example is a variable declaration assignment (section 10.5), and would only initialize the variable and not continuously drive it. That is indeed a gotcha if one just replaced all instances of wire with logic. Great comment!

Would the rules of Verilog concerning blocking assignments(=) for combinational logic always blocks and non-blocking assignments(<=) for sequential logic always block also apply to SystemVerilog ?

Hi Varun. Yes, the same rules would apply when using SystemVerilog logic. You’ll have to be more careful about which SystemVerilog logic signal is intended to be combinational and which is intended to be sequential, because they will look the same in their declaration.

i have an old power verilog model it. i am re-using it and it is giving issues in compilation

it has a statement as below: bit power_on; assign power_on = vddmp & !gndmp;

now compilation is expecting some parentheses at end of “bit power_on;” statement

can anybody help how to solve this compilation issue thanks

Hi Shaily. Thanks for your comment. Are vddmp and gndmp functional signals? Or are they power supplies?

Thanks for a very nice article.

I have a very basic question about the logic design & Verilog.

As far as I know, it is not recommended to have combinational logic include

memory such as flip-flop and latch because it is combinational!

And that is the reason why inferred flip-flops & latch should be avoided,

which is induced by not including all inputs within sensitivity list in always block, uninitialized output, etc.

My question is if the reg variable inside the always *@ block holds the value until the next assignment, it may induce the flip-flops or latches.

Is it allowed to induce a latch or flip-flop inside the combinational logic with some intentions?

Thanks a lot

Hi Jaehyuk. A always@* block will be sensitive to all input signals to the block (with one exception). Therefore, if you use a reg type inside a always@* block, it will become combinational logic and not infer flip-flop or latches.

The one exception is if the always@* calls a function or task, and that function or task contains signals that are external to the function, task, and always@* block. SystemVerilog always_comb avoids this issue, so if you code in SystemVerilog, you should use always_comb instead of always@*. See my other article on always_comb and always_ff

Helpful article, thank you Jason.

Quote: wire [7:0] my_wire_bus; // implicitly means “wire logic[15:0] my_wire_bus”

Is there a minimal width of 16 bit in SystemVerilog or something?

No there isn’t. That just happens to be the example I came up with.

Nice write-up, thanks Jason! BTW, its a nice blog, please keep it up !

Thank you, Jason, for the article! One issue I see in replacing reg with logic is that it eliminates X from the variable. That way you may miss initialization problem. I think also using UPF will force X on the registers during power-down for verification. I am not sure that with that practice it will be compatible with UPF. What do you think?

Hi Dmitry. Using the logic keyword on its own actually declares a 4-state variable, so X’s can also be represented. There is no problem with representing X’s when using UPF, low power simulation, or x-propagation. I have used logic variables successfully on projects that use all these methodologies.

Good article. I certainly appreciate this site. Keep it up! buy viagra

Hi Jason, Your articles are really helpful. Can you post something related to UVM?

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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 port assignment

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The RHS can contain any expression that evaluates to a final value while the LHS indicates a variable or net to which RHS's value is being assigned.

Procedural Assignment

Procedural assignments occur within procedures such as initial, always, task , and functions are used to place values onto variables. The variable will hold the value until the next assignment to the same variable.

The value will be placed onto the variable when the simulation executes this statement during simulation time. This can be modified and controlled the way we want by using control flow statements such as if-else-if, looping , and case statement mechanisms.

Variable Declaration Assignment

An initial value can be placed onto a variable at the time of its declaration. The assignment does not have the duration and holds the value until the next assignment to the same variable happens.

NOTE: The variable declaration assignments to an array are not allowed.

If the variable is initialized during declaration and at 0 times in an initial block as shown below, the order of evaluation is not guaranteed, and hence can have either 8'h05 or 8'hee.

Continuous Assignment

This is used to assign values onto scalar and vector nets. And it happens whenever there is a change in the RHS.

It provides a way to model combinational logic without specifying an interconnection of gates and makes it easier to drive the net with logical expressions.

Whenever b or c changes its value, the whole expression in RHS will be evaluated and updated with the new value.

Net Declaration Assignment

This allows us to place a continuous assignment on the same statement that declares the net.

NOTE: Only one declaration assignment is possible because a net can be declared only once.

Procedural continuous assignment.

These are procedural statements that allow expressions to be continuously assigned to variables or nets. And these are the two types.

1. Assign deassign: It will override all procedural assignments to a variable and deactivate it using the same signal with deassign .

The value of the variable will remain the same until the variable gets a new value through a procedural or procedural continuous assignment.

The LHS of an assign statement cannot be a part-select, bit-select, or an array reference, but it can be a variable or a combination of the variables.

2. 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 a net, part-select of a net, variable, or a net but cannot be the reference to an array and bit or part select of a variable.

The force statement will override all other assignments made to the variable until it is released using the release keyword.

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COMMENTS

  1. Verilog Ports

    Example Signed ports Port Variations Verilog 1995 Verilog 2001 onwards Ports are a set of signals that act as inputs and outputs to a particular module and are the primary way of communicating with it.

  2. hdl

    What is the correct way to assign a value to these types of variables? My code is as follows: module test (value,var); inout value; output var; reg var,value; task sendValue; begin var = 1; value = 1; end endtask endmodule and the error that I'm getting is: Error: C:/ [...]: (vlog-2110) Illegal reference to a net "value". Thanks.

  3. hdl

    1 Yes there is a difference. But not in your specific case. Using a connection directly makes that is can be uni-directional or bi-directional depending on what the underlying ports in the module are. But assign connection2 = connection1; is only uni-directional.

  4. Verilog Assignments

    An assignment has two parts - right-hand side (RHS) and left-hand side (LHS) with an equal symbol (=) or a less than-equal symbol (<=) in between. The RHS can contain any expression that evaluates to a final value while the LHS indicates a net or a variable to which the value in RHS is being assigned.

  5. fpga

    1 In verilog for Cyclone 3 I want to declare a port where some pins are inputs and some are outputs, in many examples in web i see that a port is defined like input wire [0:10]p; but what to do if i need bit0 being an input of the IC, while others be an output.

  6. PDF Verilog-2001 Quick Reference Guide

    Verilog-2001, officially the "IEEE 1364-2001 Verilog Hardware Description Language", adds several significant enhancements to the Verilog-1995 standard. • Attribute properties (page 4) • Generate blocks (page 21) • Configurations (page 43) • Combined port and data type declarations (page 8) • ANSI C style port definitions (page 8)

  7. Ports

    The Verilog-AMS Language Modules Ports Ports Ports, also referred to as pins or terminals, are used when wiring the module to other modules. As such, ports are wires. Ports declarations for simple wire are wire declarations with the keyword wire replaced by one of the following direction specifiers: input, output, or inout. For example:

  8. PDF SystemVerilog Ports & Data Types For Simple, Modeling

    To avoid extra wire and wire-bus declarations that can exist in a large Verilog design, some engineers have adopted the strategy to make the continuous assignment in the wire declaration itself, as shown in Example 2[3]. module muxff2 (q, d, clk, ce, rst_n); output q; input d, clk, ce, rst_n; reg q;

  9. Verilog Ports

    Port Direction. There are 3 directions which can be used in the port list: Input - This is used for the input ports and input is the keyword used to make an input port. Output - This is used for output port. InOut - This is used if the port is bidirectional, i.e., it can act as both input and output. inout is the keyword used for this.

  10. PDF SystemVerilog Implicit Port Connections

    port connections, and (4) using new SystemVerilog .* implicit port connections. The styles are compared for coding effort and efficiency. 2.1 Verilog positional port connections Verilog has always permitted positional port connections. The Verilog code for the positional port connections for the CALU block diagram is shown in Example 1.

  11. Modules and Ports

    A Module is a basic building design block in Verilog and it can be an element that implements necessary functionality. It can also be a collection of lower-level design blocks. As a part of defining a module, it has a module name, port interface, and parameters (optional). The port interface i.e. inputs and outputs is used to connect the high ...

  12. Verilog reg, Verilog wire, SystemVerilog logic. What's the difference

    Assigning values to Verilog reg, Verilog wire. Verilog net data types can only be assigned values by continuous assignments. This means using constructs like continuous assignment statement (assign statement), or drive it from an output port.A continuous assignment drives a net similar to how a gate drives a net.

  13. Assign Statement In Verilog

    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.

  14. Verilog Ports

    Verilog Ports. Port is an essential component of the Verilog module. Ports are used to communicate for a module with the external world through input and output. It communicates with the chip through its pins because of a module as a fabricated chip placed on a PCB. Every port in the port list must be declared as input, output or inout.

  15. Verilog Assignments

    And these are the two types. 1. Assign deassign: It will override all procedural assignments to a variable and deactivate it using the same signal with deassign. The value of the variable will remain the same until the variable gets a new value through a procedural or procedural continuous assignment.

  16. Concurrent assignment error in verilog

    Target <SUM> of concurrent assignment or output port connection should be a net type. Target <SIGNAL> of concurrent assignment or output port connection should be a net type. ... The code is to implement the trapezoidal integration method in verilog. The large number of inputs is because I want to input the data in parallel instead of serially ...