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


<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

Conditional operators can be nested to any level but it can affect readability of code.


// "y" is assigned to "out" when both "a < b" and "x % 2" are true
// "z" is assigned to "out" when "a < b" is true and "x % 2" is false
// 0 is assigned to "out" when "a < b" is false
assign out = (a < b) ?  (x % 2) ? y : z : 0;

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 (<condition>) begin
	// statement 1
end else begin
	// statement 2
end

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.


case (<expression>)
   value1: statement1;
   value2: statement2;
   ...
   default: statementN;
endcase

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.