Introduction CS3402 Digital Logic Design Reading Assignment: Chapters 0

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IntroductionCS3402Digital Logic
DesignReading Assignment Chapters 0 1
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Digital Hardware Systems
Electronic systems

• Digital Systems vs. Analog systems

• Digital vs. Analog Signals

Analog values vary over a broad range
continuously
Digital only assumes discrete values
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Digital Hardware Systems
Advantages of Digital Systems

• Analog systems slight error in input yields
  large error in output
• Digital systems are more accurate and reliable
• can deal better with degraded signals
• Digital signals are generally easier to process
• Current general purpose computers are digital
• Real life signals (e.g. human voice) are analog
• Interface circuits (i.e. sensors actuators)
  are often analog
• Digital signals are generally used as an
  approximation to real analog signals

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Binary Digital Systems
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High
Noise margin
V
Low
0
time

• The simplest digital systems are binary digital
  systems
• only two discrete values
• easier to decode
• rigorous mathematical foundation based on logic
  Boolean algebra

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Digital Hardware Systems
Digital Binary Systems
Two discrete values high voltage, high
current flowing, ON, TRUE, YES, "1" low
voltage, low current flowing, OFF, FALSE, NO,
"0"

• Advantage of binary systems
• rigorous mathematical foundation based on logic
  Boolean Algebra
• Math. Logic allows to reason about the truth of
  a set of
• statements

IF( the garage door is open) AND ( the car is
running) THEN the car can be backed out of the
garage

• the garage door is open, the car is
  running, the car can be backed out of the
  garage are logical propositions that can be
  TRUE or FALSE.
• AND is a logical operator The two preconditions
  must be True for the conclusion to be true

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Digital Hardware Systems

• Boolean Algebra
• Deals with logical propositions/statements and
  their logic values A logical statement can be
  either TRUE or FALSE ( 0 or 1).
• provides algebraic formulation of how to combine
  logic values.
• Logic operators
• At the hardware level
• Each logical statements is represented with an
  electrical signal.
• The logic value of a statement is represented
  with the signals voltage level
• Example High voltage level gt Statement is
  True
• Low voltage level gt Statement is False
• Logic operators are represented with Logic Gates

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Digital Hardware Systems
Boolean Algebra and Logical Operators
Three basic Logical Operations AND, OR, NOT
Any Boolean function can be realized using AND,
OR and NOT
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Digital Hardware Systems
Hardware Systems and Logical Operators
IF the garage door is open AND the car is
running THEN the car can be backed out of the
garage
door open?
car running?
back out car?
Low/0 High/1 Low/0 High/1
Low/0 Low/0 Low/0 High/1
Low/0 Low/0 High/1 High1
Door Open
Back out car
Car running
AND gate
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Digital Hardware Systems

• Logic gates are the standard building blocks used
  to build primitive logic operations
• Digital Technologies
• Electron Tube technology
• Electron tubes, resistors and capacitors
• interconnected with copper wire
• Discrete Transistor technology
• Resistor-Transistor Logic (RTL)
• Diode-Transistor Logic (DTL)

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Integrated Circuits (ICs)

• Integrated circuit technology
• Uses conducting, non-conducting, and
  semi-conducting (i.e. sometimes conducting )
  materials
• the basic component Transistor (electrically
  controlled switch)
• An Integrated Circuit (IC) a device (a chip)
  that contains from few to several million
  transistors
• gt Small size, low power consumption, high speed

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Integrated Circuits (ICs)

• Two Main IC Technologies
• Bipolar
• Transistor-Transistor Logic(TTL)
• Medium Power Consumption, Medium Speed
• SSI, MSI
• Emitter Coupled Logic (ECL)
• High Power Consumption, High Speed
• SSI, MSI, LSI
• CMOSComplementary Metal-Oxide-Silicon
• Low Power Consumption, Medium Speed
• VLSI

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Integrated Circuits (ICs)

• Scales of integration
• Small Scale integrated Circuits (SSI)
• ICs with 1 to 10 gates
• Independents gates
• Medium Scale integrated Circuits (MSI)
• ICs with 10 to 100 gates
• IC performs one standard function (e.g. decoder,
  Multiplexer, counter, adder, etc.)
• Large Scale integrated Circuits (LSI)
• ICs with 100 to 1000s of gates
• IC performance relatively complex functions (e.g.
  an ALU, a memory device, etc.)
• Very-Large Scale integrated Circuits (VLSI)
• Ics with 1000s to millions of gates
• Processors, Memories, etc.
• CMOS technology

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Digital Hardware Systems
CMOS Technology
Transistor basic electrical switch
three terminal switch gate, source, drain when
voltage between gate and source exceeds a certain
threshold the switch is conducting or "closed"
gt electrons flow between source and
drain when voltage is removed, the switch is
"open" or non-conducting gt connection between
source and drain is broken
Control
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Digital Hardware Systems Switches
A transistor can be represented as a switch
A switch connects two points under a control
signal. when the control signal is 0 (false),
the switch is open when it is 1 (true), the
switch is closed
Normally Open
Normally Closed
when control is 1 (true), switch is open when
control is 0 (false), switch is closed
False
False
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Implementation of AND and OR Functions with
Switches
A
B
The output is True if and only if A AND B are
True. gt this circuit realizes the AND function
False
output
Abstract Representation
AND gate
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Implementation of AND and OR Functions with
Switches

Output is True iff A is True OR B is True (or
both are True) gt The circuit realizes the OR
function
Abstract Representation
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• Semi-conductor material gt Transistors
• Transistors gt Logic Gates
• Gates gt any switching function
• Arithmetic Adders, Multipliers, Dividers, etc.
• Logic
• ALU
• Storage Devices registers, memory
• Control Devices

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Digital Systems Design Hierarchy
System-level microprocessors, storage units,
buses.
Register-level registers, adders, multipliers,
control units, etc.
Gate-level AND, OR, NOT, EX-OR gates counters,
multiplexers, decoders, laches, etc.
Transistor-level Transistors, diodes, resistors,
capacitors, etc.
This course is about logic design, not system
design (processor architecture), not
circuit design (transistor level)
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Course Coverage

• Binary Number Systems and Codes
• Boolean Algebra
• Analysis, Synthesis, and implementation of
  Combinational Circuits
• Analysis, Synthesis, and implementation of
  Sequential Circuits