digital design intro

EECS 303 Lecture 1 1

Lecture 1Introduction to Digital Logic Design

Hai Zhou

EECS 303

Advanced Digital Design

Fall 2011


Outline

• Class administration• Digital design methodology• Representations of Digital Design• Introduction to Mentor Graphics tools• READING:

– Chapter 1

– Chapter 2


Class Administration

• Lectures twice a week, Tuesday-Thursday 3:30-4:50PM• Instructor:

– Hai Zhou– Office: L461 Tech– EMAIL: [email protected]– PHONE: 491-4155

• Teaching Assistant– Peng Kang– Office: M314 Tech– EMAIL: [email protected]

• Web Page: www.eecs.northestern.edu/~haizhou/303/


Class Prerequisites

• EECS 203: Introduction to Computer Engineering– Need to have basic understanding of digital systems, logic gates,

combinational and sequential logic

• Need to have been exposed to UNIX since we will use the Mentor Graphics tools on SUN workstations

• Class will form a background for other classes in Computer Engineering– EECS 357: Introduction to VLSI CAD

– EECS 355: ASIC & FPGA Design

– EECS 361: Computer Architecture

– EECS 391: Introduction to VLSI Design


Class Administration

• Required Textbooks:– Mano and Kime, “Logic & Computer Design

Fundamentals”, Prentice Hall.

• Classnotes– Copies of lecture transparencies to be made available


Class Grades• 5 Homeworks

– 25% of grade

• 5 Labs– 25% of grade

• Midterm exam– 20% of grade

• Final exam– 30% of grade

• Homeworks and labs will be due at the beginning of class on the due date– A penalty of 10% per working day will be assigned to late assignments or

labs


Lab Work

• You will be introduced to the use of a commercial computer aided design tool from Mentor Graphics

• Will use the Sun workstations in the Wilkinson Lab (3rd floor M wing of Tech)

• Lab Hours: Open• There will be 5 labs

– Lab 1: Tutorial on Mentor Graphics (simple logic)– Lab 2: Design of combinational logic (8-bit adder)– Lab 3: Design of ALU and shifter– Lab 4: Design of a simple 8-state finites state machine– Lab 5: Use of VHDL for combinational and sequential design


The Process of Design

DesignInitial concept: what is the function performed by the object?Constraints: How fast? How much area? How much cost?Refine abstract functional blocks into more concrete realizations

Implementation

Assemble primitives into more complex building blocksComposition via wiringChoose among alternatives to improve the design

DebugFaulty systems: design flaws, composition flaws, component flawsDesign to make debugging easierHypothesis formation and troubleshooting skills

Implementation

Design

Debug


Digital SystemsDigital vs. Analog Waveforms

Analog: values vary over a broad range continuously

Digital: only assumes discrete values

+5

V

–5

T ime

+5

V

–5

1 0 1

T ime


Digital Hardware Systems

Algebra: variables, values, operations

In Boolean algebra, the values are the symbols 0 and 1 If a logic statement is false, it has value 0 If a logic statement is true, it has value 1

Operations: AND, OR, NOT

Boolean Algebra and Logical Operators

0 0 1 1

X Y X AND Y

0 1 0 1

0 0 0 1

X Y X OR Y

0 0 1 1

0 1 0 1

0 1 1 1

X NOT X

0 1

1 0


Digital Hardware Systems

Combinational logic no feedback among inputs and outputs outputs are a pure function of the inputs e.g., full adder circuit: (A, B, Carry In) mapped into (Sum, Carry Out)

Network implemented from switching elements or logicgates. The presence of feedback distinguishes between sequentialand combinational networks.

Combinational vs. Sequential Logic

- - -

X 1 X 2 X n

Switching Network

Z 1 Z 2 Z m

- - -

A B Cin

Full Adder

Sum Cout


Digital Hardware SystemsSequential logic

inputs and outputs overlap outputs depend on inputs and the entire history of execution!

network typically has only a limited number of unique configurations these are called states e.g., traffic light controller sequences infinitely through four states

new component in sequential logic networks: storage elements to remember the current state

output and new state is a function of the inputs and the old state i.e., the fed back inputs are the state!

Synchronous systemsperiod reference signal, the clock, causes the storage elements to accept new values and to change state

Asynchronous systemsno single indication of when to change state

L1

L6

L2

L3

L7

L4

L5

Case Study of a Simple Logic Design: Seven Segment Display

• Chip to drive digital display

B3 B2 B1 B0 Val L1 L2 L3 L4 L5 L6 L7

0 0 0 0 0 1 0 1 1 1 1 1

0 0 0 1 1 0 0 0 0 0 1 1

0 0 1 0 2 1 1 1 0 1 1 0

0 0 1 1 3 1 1 1 0 0 1 1

0 1 0 0 4 0 1 0 1 0 1 1

0 1 0 1 5 1 1 1 1 0 0 1

0 1 1 0 6 1 1 1 1 1 0 1

0 1 1 1 7 1 0 0 0 0 1 1

1 0 0 0 8 1 1 1 1 1 1 1

1 0 0 1 9 1 1 1 1 0 1 1

L1

L6

L2

L3

L7

L4

L5

Case Study (cont.)

Case Study (cont.)

• Implement L4:

Some gate level implementationof the Boolean function for L4


Representations of Digital Design: Switches

A switch connects two points under control signal.

when the control signal is 0 (false), the switch is open

when it is 1 (true), the switch is closed

when control is 1 (true), switch is open

when control is 0 (false), switch is closed

Normally Closed

Normally Open

Open Switch

Control

Normally Open Switch

Closed Switch

T rue

False

Open Switch

Control

Normally Closed Switch

Closed Switch

T rue

False


Switch RepresentationsExamples: routing inputs to outputs through a maze

Floating nodes: what happens if the car is not running? outputs are floating rather than forced to be false

Under all possible control signal settings (1) all outputs must be connected to some input through a path (2) no output is connected to more than one input through any path

EXAMPLE: IF car in driveway OR (car in garage AND NOT garage door closed) AND car running THEN can back out car

Car in garage Car

running

True

True

Car can back out

Garage door closed

Car in driveway

EXAMPLE: IF car in garage AND garage door open AND car running THEN back out car

T rue Car can back out

Garage door open

Car running

Car in garage


Switch Representations

Implementation of AND and OR Functions with Switches

A

False

T rue

output

B A

False

T rue

output

B

AND functionSeries connection to TRUE

OR functionParallel connection to TRUE


Representations of a Digital Design

Truth Tables

tabulate all possible input combinations and their associated output values

Example: half adder adds two binary digits to form Sum and Carry

Example: full adder adds two binary digits and Carry in to form Sum and Carry Out

NOTE: 1 plus 1 is 0 with a carry of 1 in binary

A B

0 0 1 1

0 1 0 1

Sum Carry

0 1 1 0

0 0 0 1

A 0 0 0 0 1 1 1 1

B 0 0 1 1 0 0 1 1

C in 0 1 0 1 0 1 0 1

S um 0 1 1 0 1 0 0 1

C out 0 0 0 1 0 1 1 1


Representations of Digital Design: Boolean Algebra

NOT X is written as XX AND Y is written as X & Y, or sometimes X YX OR Y is written as X + Y

values: 0, 1variables: A, B, C, . . ., X, Y, Zoperations: NOT, AND, OR, . . .

A

0011

B

0101

Sum

0110

Carry

0001

Sum = A B + A B

Carry = A B

OR'd together product terms for each truth table

row where the function is 1

if input variable is 0, it appears in complemented form;

if 1, it appears uncomplemented

Deriving Boolean equations from truth tables:


Representations of a Digital Design: Boolean Algebra

A

00001111

B

00110011

Cin

01010101

Sum

01101001

Cout

00010111

Another example:

Sum = A B Cin + A B Cin + A B Cin + A B Cin

Cout = A B Cin + A B Cin + A B Cin + A B Cin


Gate Representations of a Digital Designmost widely used primitive building block in digital system design

StandardLogic Gate

RepresentationHalf Adder Schematic

Netlist: tabulation of gate inputs & outputs and the nets they are connected to

Net: electrically connected collection of wires

Inverter

AND

OR

Net 1

Net 2

A

B

CARR Y

SUM


Representations of a Digital Design: Gates

Full Adder Schematic

Fan-in: number of inputs to a gateFan-out: number of gate inputs an output is connected to

Technology "Rules of Composition" place limits on fan-in/fan-out

Cin B A \Cin \ B \ A

A

B

Cin SUM

Cout

A B

B C in

A C in

C out


Waveform Representationdynamic behavior of a circuitreal circuits have non-zero delays

Timing Diagram of the Half Adder

sumpropagation

delay

circuit hazard: 1 plus 0 is 1, not 0!

sumpropagation

delay

Output changes are delayed from input changes

The propagation delay is sensitive to paths in the circuit

Outputs may temporarily change from the correct value to the wrong value back again to the correct value: this is called a glitch or hazard

100 200

A B SUM CARR Y


Block Representation of a Digital Designstructural organization of the design

black boxes with input and output connections

corresponds to well defined functions

concentrates on how the components are composed by wiring

Full Adder realized in terms ofcomposition of half adder blocks

Block diagram representationof the Full Adder

Sum

Cout

A

B

Cin

A

B

Sum

Carry HA

A

B

Sum

Carry HA

Sum

Cout

A

B

Cin

A

Cin

Sum

Cout

F A B


Introduction to Mentor Graphics Tools

• The Mentor Graphics CAD system has many components

• You will use a small portion of the tools for this course– Falcon Design Framework– Design Architect for entering logic designs– Quicksim for simulating the designs– QuickHDL for entering and simulating the VHDL designs

• Read through and execute Lab 1: Mentor Graphics tutorial


Introduction to Mentor Graphics

• Typing “source /vol/ece303/mgc.env” on Sun workstation will set up env for 303 labs

• Typing “dmgr” for Design Manager will create a window for running several tools

• Mentor Graphics is not a single tool but a series of design tools that uses object oriented data representation to simplify the design process

• Data created in one tool (e.g. design architect) can be shipped to another tool (e.g. quicksim) for simulation

• A schematic is merely a pictorial representation of a circuit


Viewpoints in Electronic Design Objects• Data created by DESIGN ARCHITECT is

saved in– Component

– Viewpoint

• A component is a collection of models used to describe the functional, graphical aspects– Component data is made of a schematic and a

symbol

– A symbol is a graphical model of the input and output pins

– A schematic is a functional model of how outputs are related to input values

• A viewpoint can be thought of as a filter that other applications use to process component data

Component Viewpoint

Electronic Design Object

Symbol forXOR


Moving Design Data

• Students familiar with UNIX, please refrain from using UNIX commands to move directories or files

• You MUST move these objects using the Design Manager

• Failure to use Design Manager will result in data corruption– Design Architect will store the absolute pathname to a

design

– Quicksim will try to use the symbol to look for the design from that pathname


Summary

• Class administration• Digital design methodology• Representations of Digital Design• Introduction to Mentor Graphics tools• NEXT LECTURE: Memory Elements• READING:

– Chapter 4

digital design intro

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