• 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:

VLSI Verify

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,

Verilog Tutorials

Verilog Modules and Ports Tutorial

Verilog is a hardware description language used for designing digital systems. It allows designers to define circuits and modules that can be simulated and synthesized to create hardware implementations. One of the core concepts in Verilog is modules, which are used to define the building blocks of a design. In this tutorial, we will explore Verilog modules and ports and learn how to use them effectively.

Introduction to Verilog Modules

In Verilog, a module is a block of code that represents a hardware component or a subcircuit. It encapsulates the functionality of the circuit and can be instantiated multiple times in a design. Modules promote modularity and reusability, making the design process more manageable.

Defining a Verilog Module

To define a module in Verilog, you use the module keyword, followed by the module's name and a list of its ports. Ports are the interface through which a module communicates with the rest of the design. They can be inputs, outputs, or bidirectional.

Module Ports

Ports are defined within parentheses following the module name. Each port is declared with a direction (input, output, or inout), a data type, and an optional size specification (for buses).

  • Input: Data flows into the module through input ports. They are read-only within the module.
  • Output: Data flows out of the module through output ports. They can only be assigned values within the module.
  • InOut: Bidirectional ports allow data to flow in and out of the module. They are used for bidirectional communication.

Common Mistakes with Verilog Modules and Ports

  • Forgetting to define the direction (input, output, inout) of a port.
  • Misspelling port names or using incorrect names in the module declaration and instantiation.
  • Not specifying the data type or size of the ports correctly.
  • Using blocking assignments for output ports, leading to race conditions.
  • Accidentally assigning values to input ports inside the module.

Frequently Asked Questions (FAQs)

  • Q: Can I have multiple modules in a single Verilog file? A: Yes, you can have multiple modules in a Verilog file, but only one of them can be the top-level module that represents the whole design.
  • Q: How do I instantiate a module inside another module? A: To instantiate a module, use its name followed by a unique instance name and port connections in parentheses.
  • Q: What happens if I do not specify the direction of a port? A: If you don't specify the direction of a port, it will be treated as an input by default.
  • Q: How can I pass multi-bit data through a port? A: To pass multi-bit data, use bus notation for ports (e.g., input [7:0] data_in ).
  • Q: Can I change the size of a bus in a module instantiation? A: No, the size of the bus in the instantiation must match the size of the port in the module definition.

Verilog modules and ports are essential constructs for creating complex digital designs. Modules represent hardware components, and ports define their communication interface. By understanding how to define modules, declare ports, and instantiate modules correctly, you can design efficient and modular digital circuits in Verilog.

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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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assign ports verilog

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Verilog Ports

In the previous article we covered how a block for a digital design can be defined in the Verilog using module … endmodule keywords. Let’s now move to the next part to see how we can define ports (inputs and outputs) in Verilog.

Verilog Ports Syntax

Verilog ports declaration provides the mechanism to define the signals as inputs and outputs. Syntax provided by the Verilog for ports declaration is as follows;

Syntax for Verilog Ports Declaration

So for defining Verilog ports, we need four parameters which are as follows;

  • Direction of the port
  • Size of the port
  • Type of the port
  • Name of the port

Port Direction

Direction of the port defines whether the signal we intend to use as the port is the input to the module or going out of the module as the output. input and output keywords are used to define a signal as the input and output port respectively. 

Port’s Data Type

Second field in port declaration is the data type of the port. Though Verilog provides a number of data types, only a few of them that are synthesizable and can be used for hardware design. Most commonly used data types are wire and reg type. reg is used for the signals for which we intend to store the data or their values are updated on the occurrence of some event thereby keeping the previous value retained for that length of time. While the wire type signals update their values instantly as soon as their input source changes its value.

The behaviour of this data type is almost similar to the wire used in actual hardwire in which we can store the current and it changes as soon as its input source changes its value. If we do not provide any data type for the port, it will by default be taken as wire .

Next part is the size of the port which defines how many bits of data will this port be carrying. The port size is defined using the square brackets [ ] e.g [ 7:0] . It means that the signal is a 8 bits port with bits from 7 down to 0. We can also define the port size in a more compact way using a number inside the square bracket. This number defines the size of the port in bits e.g [8] , it means that the signal is of 8 bits. So from the above discussion, [7:0] and [8] both define a port size of 8 bits. If you leave the size field blank, it defaults to 1 bit.

In the last part of the port declaration, we assign a name to the port. It is a recommended practice to have a meaningful name for the signal which depends upon its functionality. So continuing the example of AND design using Verilog, we can now define the ports for it. It has two 1-bit inputs and a 1-bit output. So now we have three signals on the port which are defined in terms of their fields as follows;

 Table for AND gate Ports

Here we can see that if we do not provide any size of the ports, it by default is 1 bit. Similarly the wire is the default data type. So now combining the port declaration with block or module definition, we get the external part of our digital design.

Verilog syntax for AND gate’s Port Declaration

As we have covered the first two components of the digital design i.e block or module definition and ports declaration, from the next article we will move to the logic part and what features Verilog provide for logic building.

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Verilog Harbor

Verilog 1995.

  • Verilog 2001 onwards

Ports are a set of signals that act as inputs press outputs to a particular module and are of primary way of communicating the itp. Think of a module as a fabricated chip positioned with a PCB and it becomes rather obvious that the only way till communicate with the raw is because its pins. Ports are enjoy kiele and have used by to design at send real receive signals from the outside world.

verilog-port

Types of Ports

Ports have by default considered because nets of type lead .

Ports declarative as inout can work as both input and outgoing.

In of code revealed below, there are three input ports, one yield port and one inout port.

It is illegal to use the same user forward multiple ports.

Signed ports

The signed attribute canned be attached to a port declaration or a net/reg declaration or both. Implicit grid have by default unsigned .

If choose the net/reg declaring does a drawn attribute, then that other shall also be considered signed.

Port Variations

Verilog has undergone a few revisions and the original IEEE version in 1995 had who following way for ports declaration. Here, module explanatory have to initially list the my for ports within the clips and then direction of who havens defined later within the body of to module. Verilog apply result of module

Verilog 2001 forth

ANSI-C style connect naming was introduced in 2001 the allowed the class the becoming specified inside the port list.

If adenine port declaration includes a earn either variable type, then that port is considered go be completely declared. It is illegal the redeclare the same port in a total or variable type declaration. And Verilog hardware description voice

Is the hook description does not include a net or variable make, then and port can be declared in a net press variable type declaration again.

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How to write Verilog Testbench for bidirectional/ inout ports

This post describes how to write a verilog testbench for bidirectional or inout ports. this happens in special designs which contain bidirectional or inout ports such as i2c core, io pads, memories, etc. .

Verilog testbench for bidirectional/ inout port

Verilog assign statement

Hardware schematic.

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 voltage.

breadboard-circuit

In Verilog, this concept is realized by the assign statement where any wire or other similar wire like data-types can be driven continuously with a value. The value can either be a constant or an expression comprising of a group of signals.

Assign Syntax

The assignment syntax starts with the keyword assign followed by the signal name which can be either a single signal or a concatenation of different signal nets. The drive strength and delay are optional and are mostly used for dataflow modeling than synthesizing into real hardware. The expression or signal on the right hand side is evaluated and assigned to the net or expression of nets on the left hand side.

Delay values are useful for specifying delays for gates and are used to model timing behavior in real hardware because the value dictates when the net should be assigned with the evaluated value.

  • LHS should always be a scalar or vector net or a concatenation of scalar or vector nets and never a scalar or vector register.
  • RHS can contain scalar or vector registers and function calls.
  • Whenever any operand on the RHS changes in value, LHS will be updated with the new value.
  • assign statements are also called continuous assignments and are always active

In the following example, a net called out is driven continuously by an expression of signals. i1 and i2 with the logical AND & form the expression.

assign-flash-1

If the wires are instead converted into ports and synthesized, we will get an RTL schematic like the one shown below after synthesis.

assign ports verilog

Continuous assignment statement can be used to represent combinational gates in Verilog.

The module shown below takes two inputs and uses an assign statement to drive the output z using part-select and multiple bit concatenations. Treat each case as the only code in the module, else many assign statements on the same signal will definitely make the output become X.

Assign reg variables

It is illegal to drive or assign reg type variables with an assign statement. This is because a reg variable is capable of storing data and does not require to be driven continuously. reg signals can only be driven in procedural blocks like initial and always .

Implicit Continuous Assignment

When an assign statement is used to assign the given net with some value, it is called explicit assignment. Verilog also allows an assignment to be done when the net is declared and is called implicit assignment.

Combinational Logic Design

Consider the following digital circuit made from combinational gates and the corresponding Verilog code.

combinational-gates

Combinational logic requires the inputs to be continuously driven to maintain the output unlike sequential elements like flip flops where the value is captured and stored at the edge of a clock. So an assign statement fits the purpose the well because the output o is updated whenever any of the inputs on the right hand side change.

After design elaboration and synthesis, we do get to see a combinational circuit that would behave the same way as modeled by the assign statement.

combinational gate schematic

See that the signal o becomes 1 whenever the combinational expression on the RHS becomes true. Similarly o becomes 0 when RHS is false. Output o is X from 0ns to 10ns because inputs are X during the same time.

combo-gates-wave

Click here for a slideshow with simulation example !

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Robert Port, who led AP investigative team that won Pulitzer for No Gun Ri massacre probe, dies

FILE - Associated Press staffer J. Robert Port poses for a photo in New York, March 6, 1995. Port, who led The AP investigative team that won a 2000 Pulitzer Prize for Investigative Reporting for the Korean War No Gun Ri massacre probe, died Saturday, Feb. 17, 2024, in Lansing, Mich. He was 68. (AP Photo/File)

FILE - Associated Press staffer J. Robert Port poses for a photo in New York, March 6, 1995. Port, who led The AP investigative team that won a 2000 Pulitzer Prize for Investigative Reporting for the Korean War No Gun Ri massacre probe, died Saturday, Feb. 17, 2024, in Lansing, Mich. He was 68. (AP Photo/File)

FILE - The Associated Press’, from left, Investigative Researcher Randy Herschaft, Special Assignment Editor J. Robert Port and Seoul newsman Sang-hun Choe pose at Columbia University during the Pulitzer Prize luncheon, May 22, 2000, in New York. Port, who led The AP investigative team that won a 2000 Pulitzer Prize for Investigative Reporting for the Korean War No Gun Ri massacre probe, died Saturday, Feb. 17, 2024, in Lansing, Mich. He was 68. (AP Photo/Kathy Willens, File)

  • Copy Link copied

LANSING, Mich. (AP) — J. Robert Port, who led The Associated Press investigative team when it won a Pulitzer for the Korean War No Gun Ri massacre probe, has died at age 68.

Port died Saturday in Lansing, Michigan, according to his sister, Susan Deller. He had been treated for cancer for more than seven years by the U.S. Department of Veterans Affairs.

Hired by The Associated Press in 1995 as special assignment editor, Port led the Pulitzer Prize-winning No Gun Ri reporting that exposed a mass killing of civilians by US troops during the Korean War.

The killings happened when U.S. and South Korean troops were being driven south by North Korean invaders, and northern infiltrators were reportedly disguising themselves as South Korean refugees.

FILE - Seth Meyers arrives at the 74th Primetime Emmy Awards on Monday, Sept. 12, 2022, in Los Angeles. Meyers celebrates his tenth year hosting "Late Night with Seth Meyers." (Photo by Richard Shotwell/Invision/AP, File)

On July 26, 1950, outside the South Korean village of No Gun Ri, civilians ordered south by U.S. troops were stopped by a battalion of the U.S. 7th Cavalry Regiment, and then attacked by U.S. warplanes. Survivors who fled under a railroad bridge were then fired on by 7th Cavalry troops for several days. Korean witnesses estimated 100 were killed in the air attack and 300 under the bridge, mostly women and children.

In the 1990s, petitions were filed by Korean survivors to U.S. authorities, demanding an investigation, an apology and compensation.

The petitions were not acted upon until, in 1999, The AP reported it had confirmed the mass killing, having found 7th Cavalry veterans who corroborated the accounts of Korean survivors. The AP also uncovered declassified files showing U.S. commanders at the time ordered units to shoot civilians in the war zone.

In 2001, the Army acknowledged the No Gun Ri killings but assigned no blame, calling it a “deeply regrettable accompaniment to a war.” President Bill Clinton issued a statement of regret, but no apology or compensation was offered.

Under Port’s guidance, The AP team had confirmed the facts of No Gun Ri by mid-1998, but publication of the previously unknown U.S. war atrocity didn’t come until the following year.

“Without Bob’s determination and smarts, up against an AP leadership troubled by such an explosive report, the exposure of a major historic U.S. war crime would not have been finally published and exposed, a full year after it was confirmed by our reporting,” said Charles Hanley, lead writer on the No Gun Ri reporting.

In 2000, The AP team, which also included reporters Sang-hun Choe and Martha Mendoza and researcher Randy Herschaft, was awarded the Pulitzer Prize for Investigative Reporting.

Port also led major investigations into illegal child labor in the U.S., which prompted a change in how laws were enforced.

Port later worked for other media organizations including the New York Daily News and The Times Union of Albany where he was also investigations editor. In 2012, the Albany County Sheriff’s appeared to retaliate against Port and his wife, Bin Cheng, after a series of stories that called into question the practices of an Albany County sheriff’s drug unit. Charges were eventually dropped.

Before joining The AP, Port worked for the St. Petersburg Times in Florida for 12 years as a team leader or lead reporter on special projects. He was also an adjunct professor at Columbia University Graduate School of Journalism for 11 years, teaching investigative techniques.

Port was born in Bryn Mawr, Pennsylvania, and attended Dickinson College in Carlisle, Pennsylvania, before entering the U.S. Air Force, serving in aircraft electronics at MacDill Air Force Base in Florida. He later obtained a bachelor of arts degree from the University of South Florida.

assign ports verilog

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  2. Verilog Assign Statement

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  3. ️ Assign in verilog. Wire And Reg In Verilog. 2019-02-05

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COMMENTS

  1. hdl

    10 I'm trying to use a bidirectional port in Verilog so I can send and receive data through it. My problem is that when I try to assign a value to the port inside a task, I keep getting an error. 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;

  2. verilog

    Oct 11, 2016 at 14:50 What is sum8? - Karan Shah Oct 12, 2016 at 2:58 @dave_59: sorry for the long delay, I've just updated the question. But it's not about how the concrete module works, but why I can read from module.port, but cannot assign to it. Maybe the question itself isn't so good in the first place. - firegurafiku Oct 12, 2016 at 16:06

  3. Verilog Ports

    Syntax Ports declared as inout can act as both input and output. input [net_type] [range] list_of_names; // Input port inout [net_type] [range] list_of_names; // Input & Output port output [net_type] [range] list_of_names; // Output port driven by a wire output [var_type] [range] list_of_names; // Output port driven by a variable Example

  4. 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:

  5. 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 ...

  6. SystemVerilog Interface Intro

    Verilog connects between different modules through its module ports. For large designs, this method of connection can become more time consuming and repetitious. Some of these ports may include signals related to bus protocols like AXI/AHB, clock and reset pins, signals to and from RAM/memory and to other peripheral devices. Using Verilog Ports

  7. Verilog Modules and Ports Tutorial

    Common Mistakes with Verilog Modules and Ports. Forgetting to define the direction (input, output, inout) of a port. Misspelling port names or using incorrect names in the module declaration and instantiation. Not specifying the data type or size of the ports correctly. Using blocking assignments for output ports, leading to race conditions.

  8. 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 inside the module

  9. Verilog Ports

    Port Name. In the last part of the port declaration, we assign a name to the port. It is a recommended practice to have a meaningful name for the signal which depends upon its functionality. So continuing the example of AND design using Verilog, we can now define the ports for it. It has two 1-bit inputs and a 1-bit output.

  10. Verilog: Are there some basic rules for port settings?

    You will assign to it in the higher-level module. Whether you declare it as a reg or not in that module depends on how it's assigned to. If it's assigned in an always block, it must be a reg. If it's assigned in an assign statement, or it's the output from another module, then it must not be a reg.

  11. Verilog Assignments

    force release Placing values onto nets and variables are called assignments. There are three basic forms: Procedural Continuous 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.

  12. Verilog Ports

    Verilog Ports - Verilog assign statement Verilog Ports Types of Ports Syntax 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.

  13. How to write Verilog Testbench for bidirectional/ inout ports

    In this post, I will give an example how to write testbench code for a digital IO pad. Basically, the IO pad has logic inputs DS, OEN, IE, PE to configure the IO pad as an input or output. When DS = OEN = IE = PE = 1, the IO pad operates as an input pad. Thus, the data from the bidirectional port PAD are written into the output C.

  14. Deciding data types of input and output ports in Verilog

    2. Why is the data type of the input inside the module and the output outside the module fixed to net. For the inputs, in the context of the module being described, there is no always or initial block assigning to that variable. Therefore it is not a reg. For the outputs, as far as the module that instantiates your module is concerned, again ...

  15. Verilog assign statement

    In Verilog, this concept is realized by the assign statement where any wire or other similar wire like data-types can be driven continuously with a value. The value can either be a constant or an expression comprising of a group of signals. Assign Syntax

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