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Chap. 2 Hierarchical Modeling Concepts
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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Design Methodology
Top-down design methodology Define the final (top) module Analyze the components which are composed of
top module step by step Bottom-up design methodology
Design the basic components Assemble basic components to larger design until
the top design is completed
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Top-down Design Methodology
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Bottom-up Design Methodology
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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4-bit Ripple Carry Counter
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Hierarchy of 4-bit Ripple Carry Counter
Top-down
Bottom-up
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Basic Component: T Flip-Flop
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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Modules
Basic component in Verilog for describing/defining a hardware
module <module_name> (<module_terminal_list>);…<module internals>……endmodule
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A module for T F.F.
module T_FF (q, clock , reset);……<functionality of T-flipflop>……endmodule
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Levels of functionality
Behavioral (algorithmic) level Dataflow level Gate level Switch level
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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Instances
Individual object of module Module is similar to “function declaration” in C,
and instance likes the concept of “function call” Instantiation
A procedure of constructing an instance using module
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Instances and Instantiation - I
Instantiation
Instances tff0, tff1, tff2, tff3
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Instances and Instantiation - II
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Illegal Module Declaration (Nested module)
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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Components of a Simulation
Design Under Test (DUT) － Design Block Test bench － Stimulus Block
Stimulus generation Output checking
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Instantiate a design under test (dut).
Stimulus Block - I
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Additional top module instantiating stimulus and design block.
Stimulus Block - II
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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A Complete Example of 4-bit Ripple Carry Counter
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T Flip-Flop
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D Flip-Flop
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Stimulus and Output Waves
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Stimulus Block (Testbench)
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Simulation results
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Hierarchical Modeling Concepts Design Methodologies 4-bit Ripple Carry Counter Modules Instances Components of a Simulation Example Summary
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Summary
Top-down v.s bottom-up design methodologies
Module is basic construction block in Verilog Instance is individual object created by modul
e A simulation consists of two components: De
sign Block and Stimulus Block
