- The Verilog-AMS Language
- Analog Processes
- 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.
Attribute | Contribution | Assignment |
|---|---|---|
Symbol | <+ | = |
Operates on | branch signals | variables |
Action | accumulates | overrides |
Order dependent | no | yes |
Evaluates | after all processes | immediately |
Formulation | implicit or explicit | explicit only |
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 Conditional Statements
In Verilog, conditional statements are used to control the flow of execution based on certain conditions. There are several types of conditional statements in Verilog listed below.
Conditional Operator
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
Conditional operators can be nested to any level but it can affect readability of code.
Here are some of the advantages of using conditional operators:
- Concise syntax : The conditional operator allows for a compact and concise representation of conditional assignments. It reduces the amount of code needed compared to using if-else statements or case statements.
- Readability : The conditional operator can enhance code readability, especially for simple conditional assignments. It clearly expresses the intent of assigning different values based on a condition in a single line.
And some disadvantages:
- Limited functionality : The conditional operator is primarily used for simple conditional assignments. It may not be suitable for complex conditions or multiple actions, as it can quickly become unreadable and difficult to maintain.
- Lack of flexibility : The conditional operator only allows for a binary choice based on the condition. It cannot handle multiple cases or multiple actions within a single line of code.
- Potential for reduced readability : While the conditional operator can enhance code readability for simple assignments, it can also make the code more difficult to understand if the condition and assigned values become complex.
if-else statement
The if-else statement allows you to perform different actions based on a condition.
If the condition evaluates to true, statement 1 is executed. Otherwise, statement 2 is executed.
Read more on Verilog if-else-if statements
case statement
The case statement is used when you have multiple conditions and want to perform different actions based on the value of a variable.
The expression is evaluated, and based on its value, the corresponding statement is executed. If none of the values match the expression, the statement under default is executed.
Read more on Verilog case statement
Procedural Assignments
Blocking assignments, race around condition: a problem with blocking assignment.
问 错误:赋值语句中的语法l-value EN
这是Verilog代码。
我得到了以下错误。你能帮我了解如何修复它们吗？
Stack Overflow用户
发布于 2020-12-20 19:35:17
您的代码中有一些语法错误。
不要使用 assign 关键字为 reg ( F1 )赋值。
不要将模块实例( sub )放在 always 块中。
使用 sub 模块实例的实例名称。
请勿创建与模块( sub )同名的 task 。在这种情况下，不需要 task/endtask 。
这是一个为我干净利落地编译的版本：
https://stackoverflow.com/questions/65377518
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"Syntax in assignment statement l-value" Why is this code not compiling?
Getting the error:
Syntax in assignment statement l-value
I've also tried " <= " instead of " = " for all the assignments in case , but I'm getting the same error.
You used a colon instead of a semicolon. Change:
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Set array of wires to integer value in Verilog test bench
I am writing a test bench for a module that takes an array of inputs that represents a number using the following code:
I want to be able to set the arrays a and b either in base 10 or in binary like I would a number. How do I go about doing this? The code that I have gives me a syntax error (ComparatorTest.v:12: Syntax in assignment statement l-value.)
Change wire to reg and you should be good to go.
And if you want to set them in binary, then you have to prefix with 4'b , like so: 4'b0000 , 4'b1111 , etc. The 4 indicates the number of bits. If you want decimal, then do 4'd0 , 4'd15 , etc.
- \$\begingroup\$ Ok thanks! Is setting the wires like that going to impact how I can do boolean algebra in the future? For example can I do this "assign bHigher = !a[0]&b[0];" in the Comparator.v \$\endgroup\$ – user146255 Commented Jul 20, 2017 at 22:39
- \$\begingroup\$ Looks fine to me. \$\endgroup\$ – alex.forencich Commented Jul 20, 2017 at 23:32
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COMMENTS
0. There are a few syntax errors with your code. Do not use the assign keyword to make an assignment to a reg ( F1 ). Do not place a module instance ( sub) inside an always block. Use an instance name for your sub module instance. Do not create a task with the same name as a module ( sub ). There is no need for the task/endtask in this case.
0. You have 2 types of syntax errors. You need to declare new_content as a reg since you make a procedural assignment to it in an always block. You need to place @ to the left of the ( in your always line. This code compiles with no errors for me: module IF_ID(new_content, instruction, newPC, clk, pwrite1); input pwrite1, clk;
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. wire [1:0] a; assign a = x & y; // Explicit assignment wire [1:0] a = x & y; // Implicit assignment.
// Example model of an AND gate wire a, b, c; assign a = b & c; 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. Net declaration assignment. This allows us to place a continuous assignment on the same statement that declares the net.
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 ...
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: a = b + c; 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.
This warning message tells you that you should use the option named when you run the command: Some Verilog syntax, especially for features added to SystemVerilog (IEEE 1800), requires you to use special options. This command fixes the errors and warnings for me: iverilog -o testbench.vvp -g2005-sv testbench.sv.
Syntax •Blocking VS non-blocking assignments = - blocking <=- non blocking, used only in always blocks Blocking Statements inside always block are executed sequentially always @(*) begin b = a; c = b; d = b; end Non Blocking Statements inside always block are executed in parallel. Value assigned to LHS are taken from "previous"values of RHS
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 ...
known value or when the predicted value is an illegitimate logic value (e.g., due to contention on a tri-state bus). Verilog also has the notion of "drive strength" but we can safely ignore this feature for our purposes. 6.111 Fall 2017 Lecture 3 9 Numeric Constants Constant values can be specified with a specific width and radix: 123 ...
The case statement is used when you have multiple conditions and want to perform different actions based on the value of a variable. case (<expression>) value1: statement1; value2: statement2; ... default: statementN; endcase. The expression is evaluated, and based on its value, the corresponding statement is executed.
Syntax: <variable> = <expression or value>. RHS expression can be a value or an expression that evaluates to a value. LHS expression can be reg, integer, real, time-variable, or memory element. The procedural assignments can be placed inside procedural blocks like initial and always blocks. They can also be placed inside tasks and functions.
我得到了以下错误。你能帮我了解如何修复它们吗？
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2. Change wire to reg and you should be good to go. And if you want to set them in binary, then you have to prefix with 4'b, like so: 4'b0000, 4'b1111, etc. The 4 indicates the number of bits. If you want decimal, then do 4'd0, 4'd15, etc. Ok thanks!