Verilog-HDL

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Verilog-HDL
Reference Verilog HDL a guide to digital design
and synthesis, Palnitkar, Samir Some of slides in
this lecture are supported by Prof. An-Yeu Wu,
E.E., NTU.
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OUTLINE

• Introduction
• Basics of the Verilog Language
• Gate-level modeling
• Data-flow modeling
• Behavioral modeling
• Task and function

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Verilog HDL (continue)

• Invented by Philip Moorby in 1983/ 1984 at
  Gateway Design Automation
• Enables specification of a digital system at a
  range of levels of abstraction switches, gates,
  RTL, and higher
• Initially developed in conjunction with the
  Verilog simulator

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Verilog HDL

• Verilog- based synthesis tool introduced by
  Synopsys in 1987
• Gateway Design Automation bought by Cadence in
  1989
• Verilog placed in public domain to compete with
  VHDL
• Open Verilog International (OVI) IEEE 1364
  -1995 and
• revised version IEEE 1364 -2001
• revised version IEEE 1364 -2005

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(No Transcript)
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What is Verilog HDL ?

• Mixed level modeling
• Behavioral
• Algorithmic ( like high level language)
• Register transfer (Synthesizable)
• Structural
• Gate (AND, OR )
• Switch (PMOS, NOMS, JFET )
• Single language for design and simulation
• Built-in primitives and logic functions
• User-defined primitives
• Built-in data types
• High-level programming constructs

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Basic Conventions

• Verilog is case sensitive
• Keywords are in lowercase
• Extra white space is ignored
• But whitespace does separate tokens
• Comments
• One liners are //
• Multiple lines / /
• Comments may not be nested

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OUTLINE

• Introduction
• Basics of the Verilog Language
• Overview of Verilog Module
• Identifier Keywords
• Logic Values
• Data Types
• Numbers Negative Numbers
• Gate-level modeling
• Data-flow modeling
• Behavioral modeling
• Task and function

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Overview of Verilog Module
Test bench
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Basic unit --Module

• module module_name (port_name)
• port declaration
• data type declaration
• module functionality or structure
• Endmodule

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D-FlipFlop

• module D_FF(q,d,clk,reset)
• output q //port declaration
• input d,clk,reset // data type declaration
• reg q
• always _at_ (posedge reset or negedge clk)
• if (reset)
• q1'b0
• else
• qd
• endmodule

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Instance

• A module provides a template which you can create
  actual objects.
• When a module is invoked, Verilog creates a
  unique object from the template
• The process of creating a object from module
  template is called instantiation
• The object is called instance

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Instances

• module adder (in1,in2,cin,sum,cout)
• .......
• endmodule

Mapping port positions
module adder8(....) adder add1(a,b,1b0,s1,c1)
// assign by order add2(.in1(a2),.in2(b2),.cin
(c1),.sum(s2) ,.cout(c2)) // assign by name,
the order is changeable ..... endmodule
Mapping names
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T-FlipFlop

• module T_FF(q,clk,reset)
• output q
• input clk,reset
• wire d
• D_FF dff0(q,d,clk,reset) // create an instance
• not n1(d,q)
• endmodule

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Identifier Keywords

• Identifier
• User-provided names for Verilog objects in the
  descriptions
• Legal characters are a-z, A-Z, 0-9, _,
  and
• First character has to be a letter or an _
• Example Count, _R2D2, FIVE
• Keywords
• Predefined identifiers to define the language
  constructs
• All keywords are defined in lower case
• Cannot be used as identifiers
• Exampleinitial, assign, module, always.

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Hierarchical Modeling Concepts
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Hierarchical Modeling Concepts

• Module ripple_carry_counter(q,clk, reset)
• Output 30 q
• Input clk, reset
• T_FF tff0(q0, clk, reset)
• T_FF tff1(q1, q0, reset)
• T_FF tff0(q2, q1, reset)
• T_FF tff0(q3, q2, reset)
• endmpdule

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Hierarchical Modeling Concepts

• module T_FF(q, clk, reset)
• output q
• input clk, reset
• wire d
• D_FF dff0(q, d, clk, reset)
• not na(d, q)
• endmodule

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Hierarchical Modeling Concepts

• module D_FF(q, d, clk, reset)
• output q
• input d, clk, reset
• reg q
• always _at_(posedge reset or negedge clk)
• if (reset)
• q1b0
• else
• qd
• endmodule

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4-bits Ripple Carry Counter
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Exercise

• module FullAdd4(a, b, carry_in, sum,
  carry_out)
• input 30 a, b
• input carry_in
• output 30 sum
• output carry_out
• wire 30 sum
• wire carry_out
• FullAdd fa0(a0, b0, carry_in, sum0,
  carry_out1)
• FullAdd fa1(a1, b1, carry_out1, sum1,
  carry_out2)
• FullAdd fa2(a2, b2, carry_out2, sum2,
  carry_out3)
• FullAdd fa3(a3, b3, carry_out3, sum3,
  carry_out)
• endmodule

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Exercise

• // FullAdd.V, ???
• module FullAdd(a, b, carryin, sum, carryout)
• input a, b, carryin
• output sum, carryout
• wire sum, carryout
• assign carryout, sum a b carryin
• endmodule

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Exercise

• Implement a 16 bits full adder by using 4 bits
  full adders.