Instances A module provides a template from which you can create actual objects. When a module is invoked, Verilog creates a unique object from the template. | Instances A module provides a template from which you can create actual objects. When a module is invoked Verilog creates a unique object from the template. Each object has its own name variables parameters and I O interface. The process of creating objects from a module template is called instantiation and the objects are called instances. In Example 2-1 the top-level block creates four instances from the T-flipflop T_FF template. Each T_FF instantiates a D_FF and an inverter gate. Each instance must be given a unique name. Note that is used to denote singleline comments. Example 2-1 Module Instantiation Define the top-level module called ripple carry counter. It instantiates 4 T-flipflops. Interconnections are shown in Section 4-bit Ripple Carry Counter. module ripple_carry_counter q clk reset output 3 0 q I O signals and vector declarations will be explained later. input clk reset I O signals will be explained later. Four instances of the module T_FF are created. Each has a unique instance is passed a set of signals. Notice that each instance is a copy of the module T_FF. T_FF tff0 q 0 clk reset T_FF tff1 q 1 q 0 reset T_FF tff2 q 2 q 1 reset T_FF tff3 q 3 q 2 reset endmodule Define the module T_FF. It instantiates a D-flipflop. We assumed that module D-flipflop is defined elsewhere in the design. Refer to Figure 2-4 for interconnections. module T_FF q clk reset Declarations to be explained later output q input clk reset wire d D_FF dff0 q d clk reset Instantiate D_FF. Call it dff0. not n1 d q not gate is a Verilog primitive. Explained later. endmodule In Verilog it is illegal to nest modules. One module definition cannot contain another module definition within the module and endmodule statements. Instead a module definition can incorporate copies of other modules by instantiating them. It is important not to confuse module definitions and instances of a module. Module definitions simply specify how the module will work its internals and its .
