Introduction to verilog basic modeling .ppt

Digital CKT

1. 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.

2. OUTLINE
Introduction
Basics of the Verilog Language
Gate-level modeling
Data-flow modeling
Behavioral modeling
Task and function

3. 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

4. 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

6. 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

7. 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

8. 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

9. Overview of Verilog Module
Test bench

10. Basic unit --Module
modulemodule_name (port_name);
port declaration
data type declaration
module functionality or structure
Endmodule

11. D-FlipFlop
module D_FF(q,d,clk,reset);
output q; //port declaration
input d,clk,reset; // data type declaration
reg q;
always @ (posedge reset or negedge clk)
if (reset)
q=1'b0;
else
q=d;
endmodule

12. 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

13. Instances
moduleadder (in1,in2,cin,sum,cout);
.......
endmodule
module adder8(....) ;
adder add1(a,b,1’b0,s1,c1) ,
add2(.in1(a2),.in2(b2),.cin(c1),.sum(s2)
,.cout(c2)) ;
.....
endmodule
Mapping port positions
Mapping names

14. 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

15. 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
Example:initial, assign, module, always….

16. Hierarchical Modeling Concepts
Top level block
Sub-
block 1
Sub-
block 1
Sub-
block 1
Sub-
block 1
Leaf
cell
Leaf
cell
Leaf
cell
Leaf
cell
Leaf
cell
Leaf
cell
Leaf
cell
Leaf
cell

17. Hierarchical Modeling Concepts
Module ripple_carry_counter(q,clk, reset);
Output [3:0] q;
Input clk, reset;
T_FF tff0(q[0], clk, reset);
T_FF tff1(q[1], q[0], reset);
T_FF tff0(q[2], q[1], reset);
T_FF tff0(q[3], q[2], reset);
endmpdule

18. 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
qd
○
clk
。
q

19. Hierarchical Modeling Concepts
module D_FF(q, d, clk, reset);
output q;
input d, clk, reset;
reg q;
always @(posedge reset or negedge clk)
if (reset)
q=1’b0;
else
q=d;
endmodule

20. 4-bits Ripple Carry Counter
Ripple carry
counter
T_FF
(tff0)
T_FF
(tff1)
T_FF
(tff2)
T_FF
(tff3)
D_
FF
Inver
ter
D_
FF
Inver
ter
D_
FF
Inver
ter
D_
FF
Inver
ter

21. Exercise
module FullAdd4(a, b, carry_in, sum, carry_out);
input [3:0] a, b;
input carry_in;
output [3:0] sum;
output carry_out;
wire [3:0] sum;
wire carry_out;
FullAdd fa0(a[0], b[0], carry_in, sum[0], carry_out1);
FullAdd fa1(a[1], b[1], carry_out1, sum[1], carry_out2);
FullAdd fa2(a[2], b[2], carry_out2, sum[2], carry_out3);
FullAdd fa3(a[3], b[3], carry_out3, sum[3], carry_out);
endmodule

22. Exercise
// FullAdd.V, 全加器
module FullAdd(a, b, carryin, sum, carryout);
input a, b, carryin;
output sum, carryout;
wire sum, carryout;
assign {carryout, sum} = a + b + carryin;
endmodule

23. Exercise
Implement a 16 bits full adder by using 4
bits full adders.