lecture2

# lecture2 - ECE 4514 Digital Design II Spring 2007 Lecture...

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ECE 4514 Digital Design II Spring 2007 Lecture 2: Hierarchical Design Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design Patrick Schaumont

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Abstraction in Hardware Design b Remember from last lecture that HDLs offer a textual description of a netlist. b Through abstraction in the HDL, we can capture more than a single transistor or gate at a time. s Similar to a function call in C that abstracts a large collection of expressions imilar to a Lego ® astle that abstracts a large collection of Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design s Similar to a Lego castle that abstracts a large collection of Lego ® bricks b Verilog offers three types of abstraction s Structural s Dataflow s Behavioral These two are related, we call both of them just 'behavioral' for now
Structural Modeling QB Q R b Describe a module in terms of components Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design b Netlist s two modules: NAND_1 and NAND_2 s net 1: Rbar to NAND_1, input_1 s net 2: Sbar to NAND_2, input_2 s net 3: NAND_1, output_1 to NAND_2, input_1 s etc . . S

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Behavioral Modeling b Describe a module in terms of input-output behavior input S, R; output Q, QB; if ( S == ‘1’) and (R == ‘0’) then Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design Set Q to ‘1’, set QB to ‘0’ else if ( S == ‘1’) and (R == ‘1’) then Set Q to ‘1’, set QB to ‘1’ else if ( S == ‘0’) and (R == ‘0’) then *Hold current state* else if ( S == ‘0’) and (R == ‘1’) then Set Q to ‘0’, set QB to ‘1’
Behavioral and Structural are dual mechanisms my_flop Rbar Sbar Q Qbar Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design Behavioral Description explains what happens to Q and Qbar in terms of Rbar and Sbar Structural Description explains what happens to Q and Qbar in terms of a netlist of lower-level components

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b A model can be expressed as behavior or structure (of lower-level models) my_flop Rbar Sbar Q Qbar Level 1 Patrick Schaumont
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## This note was uploaded on 12/24/2011 for the course ECE 4514 taught by Professor Staff during the Fall '08 term at Virginia Tech.

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lecture2 - ECE 4514 Digital Design II Spring 2007 Lecture...

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