[ Team LiB ] Continuous Assignments A continuous assignment is the most basic statement in dataflow modeling, used to drive a value onto a net. This assignment replaces gates in the description of the circuit and describes the circuit at a higher level of abstraction. | Team LiB Continuous Assignments A continuous assignment is the most basic statement in dataflow modeling used to drive a value onto a net. This assignment replaces gates in the description of the circuit and describes the circuit at a higher level of abstraction. The assignment statement starts with the keyword assign. The syntax of an assign statement is as follows. continuous_assign assign drive_strength delay3 list_of_net_assignments list_of_net_assignments net_assignment net_assignment net_assignment net_lvalue expression Notice that drive strength is optional and can be specified in terms of strength levels discussed in Section Value Set. We will not discuss drive strength specification in this chapter. The default value for drive strength is strongl and strongO. The delay value is also optional and can be used to specify delay on the assign statement. This is like specifying delays for gates. Delay specification is discussed in this chapter. Continuous assignments have the following characteristics 1. The left hand side of an assignment must always be a scalar or vector net or a concatenation of scalar and vector nets. It cannot be a scalar or vector register. Concatenations are discussed in Section Concatenation Operator. 2. Continuous assignments are always active. The assignment expression is evaluated as soon as one of the right-hand-side operands changes and the value is assigned to the left-hand-side net. 3. The operands on the right-hand side can be registers or nets or function calls. Registers or nets can be scalars or vectors. 4. Delay values can be specified for assignments in terms of time units. Delay values are used to control the time when a net is assigned the evaluated value. This feature is similar to specifying delays for gates. It is very useful in modeling timing behavior in real circuits. Examples of continuous assignments are shown below. Operators such as A and used in the examples are explained in Section Operator
