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Verilog Conditional Operator

Just what the heck is that question mark doing.

Have you ever come across a strange looking piece of Verilog code that has a question mark in the middle of it? A question mark in the middle of a line of code looks so bizarre; they’re supposed to go at the end of sentences! However in Verilog the ? operator is a very useful one, but it does take a bit of getting used to.

The question mark is known in Verilog as a conditional operator though in other programming languages it also is referred to as a ternary operator , an inline if , or a ternary if . It is used as a short-hand way to write a conditional expression in Verilog (rather than using if/else statements). Let’s look at how it is used:

Here, condition is the check that the code is performing. This condition might be things like, “Is the value in A greater than the value in B?” or “Is A=1?”. Depending on if this condition evaluates to true, the first expression is chosen. If the condition evaluates to false, the part after the colon is chosen. I wrote an example of this. The code below is really elegant stuff. The way I look at the question mark operator is I say to myself, “Tell me about the value in r_Check. If it’s true, then return “HI THERE” if it’s false, then return “POTATO”. You can also use the conditional operator to assign signals , as shown with the signal w_Test1 in the example below. Assigning signals with the conditional operator is useful!

Nested Conditional Operators

There are examples in which it might be useful to combine two or more conditional operators in a single assignment. Consider the truth table below. The truth table shows a 2-input truth table. You need to know the value of both r_Sel[1] and r_Sel[0] to determine the value of the output w_Out. This could be achieved with a bunch of if-else if-else if combinations, or a case statement, but it’s much cleaner and simpler to use the conditional operator to achieve the same goal.

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?: conditional operator in Verilog

Compact conditional operators.

Many Verilog designs make use of a compact conditional operator:

A comman example, shown below, is an “enable” mask. Suppose there is some internal signal named a . When enabled by en== 1 , the module assigns q = a , otherwise it assigns q = 0 :

The syntax is also permitted in always blocks:

Assigned Tasks

This assignment uses only a testbench simulation, with no module to implement. Open the file src/testbench.v and examine how it is organized. It uses the conditional operator in an always block to assign q = a^b (XOR) when enabled, else q= 0 .

Run make simulate to test the operation. Verify that the console output is correct. Then modify the testbench to use an assign statement instead of an always block . Change the type of q as appropriate for the assign statement.

Turn in your work using git :

Indicate on Canvas that your assignment is done.

  • Conditional Statements in Verilog

16 Sep 2021

Conditional statements in a programming language help to branch the execution of code depending on some condition. In simpler words, using these statements, the execution of specific code lines can be controlled using some conditions. Verilog provides two types of conditional statements, namely

  • Case statement

Let us explore both statements in detail.

If-else is the most straightforward conditional statement construct. For the compiler, this statement means that “If some condition is true, execute code inside if or else execute codes inside else.” The condition evaluates to be true if the argument is a non-zero number. In if-else, it is not necessary to always have an else block.

If-else-if construct is used when more than one condition needs to be checked. All the conditions are checked serially, and if none of the conditions is true, then the else block is executed.

Case Statements

Case statements are generally used when the condition is an equivalence check, which means “==” or “===”. Case statement makes the code more readable wrt to if-else if there are many conditions to check. As the name indicates, this statement will switch a particular case based on some arguments.

Again, to account for the four-state variables, there are three case statement variants: case , casez , and casex . Let us look at them in detail and also find out the difference.

In the case statement, exact matching is done. If even a single bit does not match the cases defined, the default case will be executed.

In the previous statement, we have seen that a case will be executed if it matches precisely with the argument. However, in many cases, we would not want to match the cases exactly. Consider a simple example where the master uses a select signal to select a particular slave amongst many (say, four slaves). Thus, the select line would be a 4-bit signal. A single bit needs to be high to select any slave, and the rest of the bits can be anything. Thus, instead of writing multiple cases for a slave, we can use casez. In casez, the z or ‘?’ is does not care, which means it will not be considered while comparing the case with the argument.

Casex is a bit more flexible than casez. In casex, even X is not considered during case comparison. Thus, X , Z , ? all are considered as do not care in casex. Let us see the difference between all these case statements using an example.

In the below example, the same operations are performed in different always block but using a different case statement. In the output, it can be seen that, if the value of the argument, i.e., op_code is X , then default case is executed in the case and casez construct, but for casex , the X is considered as do not care, and thus the first case is executed. When the op_code is Z , then only in the case construct the default case is executed, and for the casex and casez , Z is considered as do not care, and the 1st case is executed.

All three case statements are synthesizable, but it is not recommended to use casex and casez in designs. It is because the output after synthesis and during the simulation can differ in casex and casez. Case statements come in behavioural modelling (we will learn more about in future topics), and for complex behavioural logics, the synthesis can be different in different tools.

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

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.

conditional assignment statement in 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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Verilog Continuous Assignment Statements Tutorial

Continuous assignment statements are an essential aspect of Verilog that allows you to assign values to signals without using procedural blocks. Unlike procedural assignments found in always blocks, continuous assignments are used for modeling combinational logic. In this tutorial, we will explore continuous assignment statements in Verilog and learn how to use them to describe the behavior of combinational circuits efficiently.

Introduction to Continuous Assignment Statements

Continuous assignment statements in Verilog are used to specify the relationship between input and output signals in a combinational circuit. They allow you to assign a value to a signal continuously, meaning the assignment is continuously evaluated as the inputs change. Continuous assignments are used outside procedural blocks and are ideal for describing combinational logic or interconnections between signals.

Example of Continuous Assignment Statements:

Another example:, steps to use continuous assignment statements.

To use continuous assignment statements in Verilog, follow these steps:

  • Identify the combinational logic relationship between input and output signals.
  • Use the 'assign' keyword to create a continuous assignment statement.
  • Specify the output signal on the left-hand side and the combinational logic expression on the right-hand side of the assignment.
  • Ensure that the right-hand side expression does not contain any procedural constructs, as continuous assignments are not allowed to contain procedural statements.
  • Continuous assignments are evaluated in parallel with no explicit sequencing, making them suitable for combinational logic modeling.

Common Mistakes with Continuous Assignment Statements

  • Using procedural statements such as if-else or case statements within continuous assignments.
  • Missing the 'assign' keyword before the continuous assignment statement, leading to syntax errors.
  • Attempting to use continuous assignments for modeling sequential logic, which is not their intended use.
  • Using continuous assignments for outputs in modules with procedural assignments, leading to unexpected behavior.
  • Not considering the propagation delays of combinational logic when using continuous assignments, which may affect simulation results.

Frequently Asked Questions (FAQs)

  • Q: Can I use continuous assignments inside an always block? A: No, continuous assignments are not allowed inside always blocks. They are used outside procedural blocks to model combinational logic.
  • Q: What is the difference between continuous assignments and procedural assignments? A: Continuous assignments are evaluated continuously for combinational logic, while procedural assignments in always blocks are used for modeling sequential logic that executes based on clock edges or event triggers.
  • Q: Can I use continuous assignments for bidirectional signals? A: No, continuous assignments can only be used for assigning values to output or wire signals, not bidirectional signals or registers.
  • Q: How do continuous assignments affect the simulation time of a Verilog design? A: Continuous assignments add negligible overhead to the simulation time as they represent combinational logic and are evaluated in parallel with no explicit sequencing.
  • Q: Can I use continuous assignments for modeling arithmetic operations? A: Yes, continuous assignments can be used to model arithmetic operations in combinational logic. For example, you can use continuous assignments to describe the addition or subtraction of signals.
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  • The Verilog-AMS Language
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  • Assignment Statements

Assignment Statements 

Contribution .

A contribution statement is used to give values to continuous signals, in particular to branch potentials or flows:

This statement says that the voltage on the branch named ‘res’ should be driven so that the voltage on the branch should equal r multiplied by the current through the branch.

Contributions may be either explicit, as above, or implicit. Implicit contributions have the target on both sides of the contribution operator. For example:

This implements the series combination of a resistor and a capacitor.

Implicit contributions to branch flows can be used to easily create series combinations whereas implicit contributions to branch potentials can be used to create parallel combinations. For example, the following creates the parallel combination of an inductor and a conductor:

Multiple contributions to the same branch in the same analog process accumulate. For example:

This is equivalent to:

Multiple contributions to a branch flow can be viewed as creating multiple parallel branches. For example, the above example is equivalent to the parallel combination of the output of a controlled current source, a conductor, and a capacitor. Similarly, multiple contributions to a branch potential can be viewed as creating multiple series branches.

The target (left side) must be a branch signal: an access function applied to a continuous branch. The branch may be a named (or explicit) branch, or it may be an unnamed (or implicit) branch, which are given as a single net or a pair of nets. When an implicit branch is given as a pair of nets, the branch is assumed to connect the two nets. When an implicit branch is specified as a single net, the branch is assumed to connect that net to ground.

Here is a resistor module that uses a explicitly declared or named branch:

Here is a resistor module that uses a implicitly declared or unnamed branch:

Descriptions that employ unnamed branches are a little more compact, but also the formulation of the branches is constrained (multiple contributions to flows give a shunt toplogy and to potentials gives a series topology). For this reason people use unnamed branches with the branch topology is simple, and switch to named branches for the more complicated topologies.

The actual contributions occur after the analog block has been evaluated, meaning that the branch values do not change between statements in the analog block. As such, so as long as the values of the right-hand side expressions are not affected, the order of the contribution statements is inconsequential. So for example, these two analog blocks are equivalent:

Indirect Assignment 

An indirect assignment is an alternative to the contribution statement. It also drives a particular branch potential or flow so that a given equation is satisfied, but in this case the driven branch potential or flow need not be in the specified equation. This feature is rarely needed, however it occasionally allows you to describe a component that would cumbersome to describe with contributions. For example, it is possible to describe an ideal opamp using:

This can be read as ‘drive V(out) such that V(pin,nin) == 0’.

The left side of the equation must be either a branch potential or flow, the right side is an expression. The equation may be implicit or explicit.

The driven branch must not also be a target of a contribution statement.

Assignment 

A assignment evaluates the expression on its right hand side and then immediately assigns the value to the variable on its left hand side:

The target (left side) of an analog assignment statement may only be a integer or real variable. It may not be signal or a wire.

Contribution versus Assignment 

For people new to Verilog-A and Verilog-AMS, contribution and assignment seem to be doing very similar things, and this can confuse them. Here the differences between contribution and assignment are highlighted.

Using Continuous Assignment to Model Combinational Logic in Verilog

In this post, we talk about continuous assignment in verilog using the assign keyword. We then look at how we can model basic logic gates and multiplexors in verilog using continuous assignment.

There are two main classes of digital circuit which we can model in verilog – combinational and sequential .

Combinational logic is the simplest of the two, consisting solely of basic logic gates, such as ANDs, ORs and NOTs. When the circuit input changes, the output changes almost immediately (there is a small delay as signals propagate through the circuit).

In contrast, sequential circuits use a clock and require storage elements such as flip flops . As a result, output changes are synchronized to the circuit clock and are not immediate.

In this post, we talk about the techniques we can use to design combinational logic circuits in verilog. In the next post, we will discuss the techniques we use to model basic sequential circuits .

Continuous Assignment in Verilog

We use continuous assignment to drive data onto verilog net types in our designs. As a result of this, we often use continuous assignment to model combinational logic circuits.

We can actually use two different methods to implement continuous assignment in verilog.

The first of these is known as explicit continuous assignment. This is the most commonly used method for continuous assignment in verilog.

In addition, we can also use implicit continuous assignment, or net declaration assignment as it is also known. This method is less common but it can allow us to write less code.

Let's look at both of these techniques in more detail.

  • Explicit Continuous Assignment

We normally use the assign keyword when we want to use continuous assignment in verilog. This approach is known as explicit continuous assignment.

The verilog code below shows the general syntax for continuous assignment using the assign keyword.

The <variable> field in the code above is the name of the signal which we are assigning data to. We can only use continuous assignment to assign data to net type variables.

The <value> field can be a fixed value or we can create an expression using the verilog operators we discussed in a previous post. We can use either variable or net types in this expression.

When we use continuous assignment, the <variable> value changes whenever one of the signals in the <value> field changes state.

The code snippet below shows the most basic example of continuous assignment in verilog. In this case, whenever the b signal changes states, the value of a is updated so that it is equal to b.

  • Net Declaration Assignment

We can also use implicit continuous assignment in our verilog designs. This approach is also commonly known as net declaration assignment in verilog.

When we use net declaration assignment, we place a continuous assignment in the statement which declares our signal. This can allow us to reduce the amount of code we have to write.

To use net declaration assignment in verilog, we use the = symbol to assign a value to a signal when we declare it.

The code snippet below shows the general syntax we use for net declaration assignment.

The variable and value fields have the same function for both explicit continuous assignment and net declaration assignment.

As an example, the verilog code below shows how we would use net declaration assignment to assign the value of b to signal a.

Modelling Combinational Logic Circuits in Verilog

We use continuous assignment and the verilog operators to model basic combinational logic circuits in verilog.

To show we would do this, let's look at the very basic example of a three input and gate as shown below.

To model this circuit in verilog, we use the assign keyword to drive the data on to the and_out output. This means that the and_out signal must be declared as a net type variable, such as a wire.

We can then use the bit wise and operator (&) to model the behavior of the and gate.

The code snippet below shows how we would model this three input and gate in verilog.

This example shows how simple it is to design basic combinational logic circuits in verilog. If we need to change the functionality of the logic gate, we can simply use a different verilog bit wise operator .

If we need to build a more complex combinational logic circuit, it is also possible for us to use a mixture of different bit wise operators.

To demonstrate this, let's consider the basic circuit shown below as an example.

To model this circuit in verilog, we need to use a mixture of the bit wise and (&) and or (|) operators. The code snippet below shows how we would implement this circuit in verilog.

Again, this code is relatively straight forward to understand as it makes use of the verilog bit wise operators which we discussed in the last post.

However, we need to make sure that we use brackets to model more complex logic circuit. Not only does this ensure that the circuit operates properly, it also makes our code easier to read and maintain.

Modelling Multiplexors in Verilog

Multiplexors are another component which are commonly used in combinational logic circuits.

In verilog, there are a number of ways we can model these components.

One of these methods uses a construct known as an always block . We normally use this construct to model sequential logic circuits, which is the topic of the next post in this series. Therefore, we will look at this approach in more detail the next blog post.

In the rest of this post, we will look at the other methods we can use to model multiplexors.

  • Verilog Conditional Operator

As we talked about in a previous blog, there is a conditional operator in verilog . This functions in the same way as the conditional operator in the C programming language.

To use the conditional operator, we write a logical expression before the ? operator which is then evaluated to see if it is true or false.

The output is assigned to one of two values depending on whether the expression is true or false.

The verilog code below shows the general syntax which the conditional operator uses.

From this example, it is clear how we can create a basic two to one multiplexor using this operator.

However, let's look at the example of a simple 2 to 1 multiplexor as shown in the circuit diagram below.

The code snippet below shows how we would use the conditional operator to model this multiplexor in verilog.

  • Nested Conditional Operators

Although this is not common, we can also write code to build larger multiplexors by nesting conditional operators.

To show how this is done, let's consider a basic 4 to 1 multiplexor as shown in the circuit below.

To model this in verilog using the conditional operator, we treat the multiplexor circuit as if it were a pair of two input multiplexors.

This means one multiplexor will select between inputs A and B whilst the other selects between C and D. Both of these multiplexors use the LSB of the address signal as the address pin.

To create the full four input multiplexor, we would then need another multiplexor.

This takes the outputs from the first two multiplexors and uses the MSB of the address signal to select between them.

The code snippet below shows the simplest way to do this. This code uses the signals mux1 and mux2 which we defined in the last example.

However, we could easily remove the mux1 and mux2 signals from this code and instead use nested conditional operators.

This reduces the amount of code that we would have to write without affecting the functionality.

The code snippet below shows how we would do this.

As we can see from this example, when we use conditional operators to model multiplexors in verilog, the code can quickly become difficult to understand. Therefore, we should only use this method to model small multiplexors.

  • Arrays as Multiplexors

It is also possible for us to use verilog arrays to build simple multiplexors.

To do this we combine all of the multiplexor inputs into a single array type and use the address to point at an element in the array.

To get a better idea of how this works in practise, let's consider a basic four to one multiplexor as an example.

The first thing we must do is combine our input signals into an array. There are two ways in which we can do this.

Firstly, we can declare an array and then assign all of the individual bits, as shown in the verilog code below.

Alternatively we can use the verilog concatenation operator , which allows us to assign the entire array in one line of code.

To do this, we use a pair of curly braces - { } - and list the elements we wish to include in the array inside of them.

When we use the concatenation operator we can also declare and assign the variable in one statement, as long as we use a net type.

The verilog code below shows how we can use the concatenation operator to populate an array.

As verilog is a loosely typed language , we can use the two bit addr signal as if it were an integer type. This signal then acts as a pointer that determines which of the four elements to select.

The code snippet below demonstrates this method in practise. As the mux output is a wire, we must use continuous assignment in this instance.

What is the difference between implicit and explicit continuous assignment?

When we use implicit continuous assignment we assign the variable a value when we declare. When we use explicit continuous assignment we use the assign keyword to assign a value.

Write the code for a 2 to 1 multiplexor using any of the methods discussed we discussed.

Write the code for circuit below using both implicit and explicit continuous assignment.

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IMAGES

  1. 😍 Verilog assignment. Conditional Operator. 2019-02-03

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  2. Register Cannot Driven by Primitives or Continuous Assignment

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  3. 😍 Verilog assignment. Conditional Operator. 2019-02-03

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COMMENTS

  1. Verilog Conditional Statements

    <variable> = <condition> ? <expression_1> : <expression_2>; The conditional operator allows you to assign a value to a variable based on a condition. If the condition is true, expression_1 is assigned to the variable. Otherwise, expression_2 is assigned. Nested conditional operators

  2. Conditional Operator

    Assigning signals with the conditional operator is useful! 1 2 3 4 5 6 7 8 9 10 11 12 13 module test2; reg r_Check = 1'b1; wire w_Test1; assign w_Test1 = r_Check ? 1'b1 : 1'b0; initial begin #1; $display ("OUTPUT: %s", r_Check ?

  3. Conditional Assignment in Verilog

    Conditional Assignment in Verilog Ask Question Asked 1 year, 4 months ago Modified 1 year, 4 months ago Viewed 3k times 1 I came across this code and was hoping someone could help me with it. I understand that this means that out equals to out_1 if either a0, a1, a2, a3 is 1. If not, we have to look at the second expression which is 1'd0.

  4. Verilog conditional assignments without using procedural blocks like

    Verilog conditional assignments without using procedural blocks like VHDL with/select Asked 2 years, 10 months ago Modified 2 years, 10 months ago Viewed 831 times 4 I am trying to find a way to conditionally assign values to a signal in verilog similar to the with/select in VHDL.

  5. Verilog Conditional Statements Tutorial

    Conditional statements in Verilog provide a way to control the flow of your code based on certain conditions. They are essential for implementing decision-making logic and creating complex behaviors in digital designs. The three primary conditional statements in Verilog are if, else if, and case . Verilog if Statement

  6. Verilog if-else-if

    Verilog if-else-if. This conditional statement is used to make a decision on whether the statements within the if block should be executed or not. If the expression evaluates to true (i.e. any non-zero value), all statements within that particular if block will be executed. If it evaluates to false (zero or 'x' or 'z'), the statements inside if ...

  7. ?: conditional operator in Verilog

    It uses the conditional operator in an always block to assign q = a^b (XOR) when enabled, else q= 0. Run make simulate to test the operation. Verify that the console output is correct. Then modify the testbench to use an assign statement instead of an always block. Change the type of q as appropriate for the assign statement. Turn in your work ...

  8. Storing value of a conditional assignment in Verilog

    Assume I have the follow assignment. wire COND; assign COND = A & B; The values of A and B are changing between true and false, however, once they both hit 1 at the same time and COND = 1; I wish to keep this COND as a true value (sort of like a trigger) instead of it reverting to 0 when A and B changes.

  9. Conditional Statements

    Conditional Statements If Statements An if statement evaluates an expression and executes the subsequent statement if the expression evaluates to true, otherwise it skips that statement. For example: if (i > max_count) i = 0;

  10. Assignment Statements

    Blocking Assignment. A blocking assignment evaluates the expression on its right hand side and then immediately assigns the value to the variable on its left hand side: a = b + c; It is also possible to add delay to a blocking assignment. For example: a = #10 b + c; In this case, the expression on the right hand side is evaluated and the value ...

  11. Conditional Statements in Verilog

    Verilog provides two types of conditional statements, namely If-else Case statement Let us explore both statements in detail. If-else If-else is the most straightforward conditional statement construct. For the compiler, this statement means that "If some condition is true, execute code inside if or else execute codes inside else."

  12. Conditional Statements

    Conditional Statements If Statements An if statement evaluates an expression and executes the subsequent statement if the expression evaluates to true, otherwise it skips that statement. For example: if (i > max_count) i = 0;

  13. PDF Advanced Verilog

    • Non-blocking assignments literally do not blockthe execution of the next statements. The right side of all statements are determined first, then the left sides are assigned together. - Consequently, non-blocking assignments result in simultaneous or parallel statement execution. For example: assume a = b = 0 initially; a <= 1; b <= a;

  14. Conditional Operator (?:)

    The conditional operator (?:), also known as the ternary operator, is a unique operator in SystemVerilog that takes three operands: a condition, a value if the condition is true, and a value if the condition is false. It serves as a shorthand way of writing an if-else statement. The syntax is as follows: condition ? value_if_true : value_if_false.

  15. Verilog assign statement

    Verilog assign statement Assign Syntax Rules Example #1 Example #2 Assign reg variables Implicit Continuous Assignment Combinational Logic Design 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.

  16. Verilog Continuous Assignment Statements Tutorial

    Continuous assignment statements in Verilog are used to specify the relationship between input and output signals in a combinational circuit. They allow you to assign a value to a signal continuously, meaning the assignment is continuously evaluated as the inputs change.

  17. Assignment Statements

    Assignment Statements Contribution A contribution statement is used to give values to continuous signals, in particular to branch potentials or flows: analog begin V (res) <+ r * I (res); end

  18. vhdl

    3 Answers Sorted by: 18 That's a ternary operator. It's shorthand for an if statement Format: condition ? if true : if false Example: tone [23] ? clkdivider-1 : clkdivider/2-1 Translates to something like (not correct syntax but I think you'll get it): if tone [23] is 1, counter = clkdivider-1 else counter = clkdivider/2-1

  19. Using Continuous Assignment to Model Combinational Logic in Verilog

    July 14, 2020 In this post, we talk about continuous assignment in verilog using the assign keyword. We then look at how we can model basic logic gates and multiplexors in verilog using continuous assignment. There are two main classes of digital circuit which we can model in verilog - combinational and sequential.