chapter 2: fundamentals of digital electronics dr mohamed menacer taibah university 2007-2008
TRANSCRIPT
Chapter 2:Chapter 2:Fundamentals of Fundamentals of Digital ElectronicsDigital Electronics
Dr Mohamed MenacerDr Mohamed MenacerTaibah UniversityTaibah University
2007-20082007-2008
AbstractAbstract
• The basics of Boolean algebra will be introduced, starting from simple combinational logic functions and basic sequential logic circuits such as latches and flip-flops. • Transistor basics will be reviewed and circuits introduced that demonstrate implementations of the basic logic elements in TTL/CMOS technology. • Based on these fundamentals, more complex logic structures such as decoders, adders, registers, and memories will constructed and their performance analyzed. • The logic functions used as the architectural basis for programmable devices used in spaceborne electronics will be examined and analyzed.
OutlineOutline
IntroductionIntroduction
Basic LogicBasic Logic
Hardware (Transistors, Gates)Hardware (Transistors, Gates)
Combinational LogicCombinational Logic
Sequential LogicSequential Logic
Module Design in Programmable DevicesModule Design in Programmable Devices
Basic Digital LogicBasic Digital Logic
Logic ValuesLogic Values
For binary hardwareFor binary hardware Either a ‘1’ or a ‘0’Either a ‘1’ or a ‘0’ ““Most of the time”Most of the time”
Other types of hardware can be have Other types of hardware can be have more than two valuesmore than two values
Simulation can use a multi-value logic Simulation can use a multi-value logic systemsystem VHDL Std_Logic uses a nine-valued logicVHDL Std_Logic uses a nine-valued logic
Binary Hardware Logic ValuesBinary Hardware Logic Values
Logic ‘1’Logic ‘1’
Logic ‘0’Logic ‘0’
Undefined valueUndefined value
TTL Logic LevelsTTL Logic Levels
Logic ‘1’ threshold - VLogic ‘1’ threshold - VIHIH
2.0 V2.0 V
Logic ‘0’ threshold - VLogic ‘0’ threshold - VILIL
0.8 V0.8 V
UndefinedUndefined0.8 V < v < 2.0 V0.8 V < v < 2.0 V
TTL Logic LevelsTTL Logic LevelsExamples of Undefined Examples of Undefined
ValuesValuesFloating signals may take on illegal valuesFloating signals may take on illegal values
What happens during a signal transition?What happens during a signal transition?
0.8V
2.0V
Logic ‘0’
Undefined
Logic ‘1’
Logic Values and Basic Logic Values and Basic FunctionsFunctions
Logic ValuesLogic Values
LevelsLevels '0' or '1''0' or '1'
PulsesPulses Presence or absence of pulsesPresence or absence of pulses Pulse widthsPulse widths Number of pulsesNumber of pulses
Zero crossingsZero crossings
5Digital Waveform
Time
Vol
tage
(V
) 1
0
1
Switching AlgebraSwitching Algebra
Two-valued variable from {0,1}Two-valued variable from {0,1}
Two binary operationsTwo binary operations AND ( • )AND ( • ) OR ( + )OR ( + )
One unary operationOne unary operation NOT ( NOT ( ) )
Unary Operation - NOTUnary Operation - NOT
A Y
0 1
1 0
NOT OperatorTruth Table
A B
The NOT gate reverses the inputThe NOT gate reverses the input
Binary Operation - ANDBinary Operation - AND
A B Y
0 0 0
0 1 0
1 0 0
1 1 1
AND means that both AND means that both conditions must be conditions must be truetrue in order in order for the conclusion to be for the conclusion to be truetrue
AInputs
B
Output
Binary Operation - [Inclusive] Binary Operation - [Inclusive] OROR
A B Y
0 0 0
0 1 1
1 0 1
1 1 1
Another basic operator is the ORAnother basic operator is the OROR works such that the output is OR works such that the output is truetrue, if either of the two inputs is , if either of the two inputs is truetrue
DigitalDigital XORXOR
We can build an electrical device that performs the logical We can build an electrical device that performs the logical XOR operation on voltage equivalents of logic valuesXOR operation on voltage equivalents of logic values
An XOR gate has the An XOR gate has the electrical schematic:electrical schematic:
XOR OperatorTruth Table
0 0 0A B Output
0 1 11 0 11 1 0
A
InputsOutput
B
All digital computers are built All digital computers are built using only three gate types: using only three gate types:
AND, OR, and NOTAND, OR, and NOT
TransistorsTransistors
Transistor DefinitionsTransistor Definitions
MOS - Metal Oxide SemiconductorMOS - Metal Oxide Semiconductor
FET - Field Effect TransistorFET - Field Effect Transistor
BJT - Bipolar Junction TransistorBJT - Bipolar Junction Transistor
TransistorTransistor
npn bipolar transistor
collector
base
emitter
NAND
NOR NOT