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lecture2 - ECE 4514 Digital Design II Spring 2007 Lecture 2...

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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 boxshadowdwn Remember from last lecture that HDLs offer a textual description of a netlist. boxshadowdwn Through abstraction in the HDL, we can capture more than a single transistor or gate at a time. square4 Similar to a function call in C that abstracts a large collection of expressions square4 Similar to a Lego ® castle that abstracts a large collection of Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design Lego ® bricks boxshadowdwn Verilog offers three types of abstraction square4 Structural square4 Dataflow square4 Behavioral These two are related, we call both of them just 'behavioral' for now
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Structural Modeling QB Q R S boxshadowdwn Describe a module in terms of components Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design boxshadowdwn Netlist square4 two modules: NAND_1 and NAND_2 square4 net 1: Rbar to NAND_1, input_1 square4 net 2: Sbar to NAND_2, input_2 square4 net 3: NAND_1, output_1 to NAND_2, input_1 square4 etc ..
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Behavioral Modeling boxshadowdwn 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’
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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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Structural and Behavioral are related boxshadowdwn A model can be expressed as behavior or structure (of lower-level models) my_flop Rbar Sbar Q Qbar Level 1 Patrick Schaumont Spring 2008 ECE 4514 Digital Design II Lecture 2: Hierarchical Design Q Qbar Sbar Rbar NAND NAND Level 2
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