The Grunt Work of Design
• Many design tasks require a lot of time and effort
• Forming logic expressions (Truth tables)
• Reducing logic complexity (Boolean Algebra)
• Making schematics
• Analyzing logic circuits
• Design changes require starting over at the
beginning
• Re-design, Re-do logic reduction, Re-analyze
• Computers can come to our rescue!
• Computer Aided Design tools - CAD
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-1
CAD Tools
• In logic design, CAD tools help us in:
• Design Entry
• Composing a design in a way that is easily
understood by computers and people
• Logic Synthesis
• Forming logic equations from higher-level
concepts
• Reducing the complexity of logic equations
• Simulation
• Predicting how the resulting circuit will behave
• Implementation
• Building an actual circuit for your logic
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-2
Design Entry
• Designs can be entered in
many different forms
• Schematics
D
A
B
C
B
A
C
D
• Truth tables
• Programming languages
• Waveforms
f<=(x1 AND x2)OR(NOT(x3 AND x2));
g<=(x1 OR x3)AND(x2 OR (NOT(x1)))
• Combinations of all the
a
a
0
0
0
0
1
1
1
1
b
0
0
1
1
0
0
1
1
c
0
1
0
1
0
1
0
1
F
0
1
1
1
0
1
1
0
above
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-3
VHDL
• VHSIC Hardware Description Language
• Represents digital signals as variables
• Major parts
• ENTITY
• Describes high-level interfaces
• Inputs and Outputs
• ARCHITECTURE
• Describes actual logical function or behavior of
circuit
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-4
VHDL Entities
• ENTITY describes high-level interface
Name of ENTITY
(note: must be same
as file name)
Inputs to sevensegment
ENTITY sevensegment IS
PORT (A,B,C,D: IN BIT;
sa,sb,sc,sd,se,sf,sg: OUT BIT);
END sevensegment;
End of ENTITY
Outputs from sevensegment
WARNING: Syntax is critical and compiler is unforgiving
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-5
VHDL Architectures
• Architecture describes what to actually implement
• Should describe each output in terms of inputs
D
B
A
B
C
sa
A
Describing logical
function
Name of entity
this is part of
C
D
Definition
of outputs
ARCHITECTURE LogicFunc OF sevensegment IS
sa <= (A OR B OR C OR (NOT D)) AND
(A OR (NOT B) OR C OR D);
sb <= …..
END LogicFunc;
Function in terms of AND, OR, NOT, NAND, NOR, XOR, XNOR
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-6
Synthesis
• Synthesis – Converting various forms of logic
representations into better representations
• Inputs –
• Schematics, Truth tables, VHDL, Waveforms
• Outputs –
• A single logical description of the entire system,
in various representation
• May be optimized according to user-specified
criteria
• Smallest form, Fastest form, etc.
• Synthesis mechanisms
• Boolean algebra, related algorithms
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-7
Simulation
• Simulation predicts how the circuit will perform
• Functional Simulation
• Predicts only the logical operation of the circuit
• Fast
• Timing Simulation
• Predicts the actual timing operation of the circuit
• Requires knowledge of how the circuit will be implemented
Inputs
1
A
0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
1
1
1
1
0
0
0
0
0
1
1
1
0
1
1
1
0
1
1
1
0
0
0
0
1
B
C
0
1
0
1
T1
T2
0
1
0
1
Z
0
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-8
Altera CAD Tools
• CAD tools that include:
• Design entry
• Synthesis
• Simulation (functional or timing)
• Implementation (in Altera PLDs and FPGAs)
• Student version:
• Implementation portion limited to a small variety of
Altera PLDs/FPGAs
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-9
Designing with Altera Quartus
1. Create a new design
2. Input design using various design entry tools
Graphical (Schematic)
Truth Tables
Waveforms
Textual (VHDL, AHDL)
3. Synthesize Design (Functional)
Errors?
4. Functional Simulation
5. Synthesize Design for Implementation
6. Timing Simulation
Timing wrong?
7. Implement in Hardware
 Seattle Pacific University
EE 1210 - Logic System Design
CAD-VHDL-10
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