Embedded Systemasds Lecture

7/29/2019 Embedded Systemasds Lecture

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Embedded Systems


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Real Time Embedded System

Real Time

Timing generated for our requirements

Embedded

Number of systems co exist to perform a specific

function in real time


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Characteristics of RTES

Singled functioned

Tightly constrained

Reactive and Real time


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Embedded system Architecture


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Common Examples of Embedded

Systems

Consumer Electronics


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Home Appliance


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Office Automation


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Business equipment


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Automobile


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Mobile Phone

A circuit board

Antenna

Microphone Speaker LCD

Keyboard

Battery


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Block Diagram


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Components of an Embedded System

Microprocessor

Memory

Input Output Devices and Interfaces Software


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Constraints in Developing Embedded

Systems

Design Issues

Design Metrics NRE Cost

Unit Cost

Size Performance

Power Consumption

Flexibility

Time to prototype Time to market

Maintainability

Correctness


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Design Methodology

System Level Design

Sub system Design

Process Level Design Task Level Design


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hierarchical Components of

embedded system


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Structure of an Embedded system


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Processors

General purpose processors

Microcontrollers

Digital signal processors


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Architecture of general purpose

processor

Pentium 4

8085


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Architecture of a microcontroller

8051

AVR

Microcon

trollers


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Architecture of Digital Signal Processor

Harvard Architecture


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Difference between Microcontroller

and MicroprocessorMicrocontroller Microprocessor

On a single chip External RAM, ROM, decoder, A/D

converters are separate

Small in size Big in size

Less expensive ExpensiveNon flexible Flexible

Less time High Development Time

8051 8086


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Typical microcontroller system


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Typical microprocessor system


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Characteristics of DSP

Signal processing applications

Harvard architecture

Two or four memory accesses percycle

Dedicated hardware perform allarithmetic operations in one cycle

Complex instructions

Multiple operations per instruction

Dedicated address generation units

Specialized addressing

Interrupts disabled during someoperations


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Characteristics of general purpose

processor

Von Neumann Architecture

1 access per cycle

Most operations in more than

one cycle One operation per instruction

No separate addressgeneration units

General purpose addressingmodes

Interrupts rarely disabled


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Input Output Devices and interface

chips


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Memory

Processor memory

Internal on chip memory

Primary memory Cache memory

Secondary memory


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Operations on memory

Memory Read operation

Memory write operation


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Data Storage

M = words

N= bits

M X N = word memory K = log2(M); No. of address lines


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Memory Specifications

Power Consumption

Write ability High end(RAM)

Middle range(FLASH, EEPROM)

Lower range(Programmer) Low end (ROM)

Storage permanence High end(ROM)

Middle range(NVRAM)

Lower range(SRAM)

Low end(DRAM)


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ROM (Read Only Memory)

NonVolatile

Memory

Store software

program


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Masked programmed ROM

Connections Programmed at fabrication

Stores data forever

Connections never change unless damaged


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OTP ROM

Programmed after manufacture

Provides files of desired content

Connection is like a fuse and blows when

connection should not exist

Very low ability to write


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EPROM(Erasable Programmable ROM )

Better ability to write

Reduced storage permanence (10 yrs)

Used in design development

When exposes to UV erases everything


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EEPROM

Erased by using higher than normal voltage

Can program and erase individual words

Same characteristics as that of EPROM

Expensive


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Flash Memory

Extension of EEPROM

Large blocks of memory can be erased at once

Used in embedded systems for storing large

data items in non volatile memory


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RAM(Random Access Memory)

Volatile memory

Read and writteneasily

Internal structurecomplex than ROM

A word consists ofseveral memory cells

Each IP/OP line

connected to each cell Rd/Wr connected to

every cell


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SRAM (static RAM)

Memory cells uses flip flops

Holds data as long as power supplies


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DRAM

Memory cells uses transistors and capacitors

Compact than SRAM

Slower


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Memory Hierarchy


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Digital signal processing


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Signal Processing


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A to D and D to A process


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Signal Conditioning

Provide Distinct enhancements to both the

performance and accuracy of data acquisition

system


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Amplification

Increases the voltage level to better match the

analog-to-digital converter (ADC) range, thus

increasing the measurement resolution and

sensitivity. In addition, using external signalconditioners located closer to the signal

source, or transducer, improves the

measurement signal-to-noise ratio bymagnifying the voltage level before it is

affected by environmental noise.


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Attenuation

Attenuation, the opposite of amplification, is

necessary when voltages to be digitized are

beyond the ADC range. This form of signal

conditioning decreases the input signalamplitude so that the conditioned signal is

within ADC range. Attenuation is typically

necessary when measuring voltages that aremore than 10 V.


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Isolation

Isolated signal conditioning devices pass the

signal from its source to the measurement

device without a physical connection by using

transformer, optical, or capacitive couplingtechniques. In addition to breaking ground

loops, isolation blocks high-voltage surges and

rejects high common-mode voltage and thusprotects both the operators and expensive

measurement equipment.


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Filtering

Filters reject unwanted noise within a certain

frequency range. Oftentimes, low-pass filters

are used to block out high-frequency noise in

electrical measurements, such as 60 Hz power.Another common use for filtering is to

prevent aliasing from high-frequency signals.

This can be done by using an anti-aliasing filterto attenuate signals above the Nyquist

frequency


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Linearization

Linearization is necessary when sensors

produce voltage signals that are not linearly

related to the physical measurement.

Linearization is the process of interpreting the

signal from the sensor and can be done either

with signal conditioning or through software.

Thermocouples are the classic example of asensor that requires linearization.


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Cold-Junction Compensation

Cold-junction compensation (CJC) is a technologyrequired for accurate thermocouple measurements.Thermocouples measure temperature as the differencein voltage between two dissimilar metals.

Based on this concept, another voltage is generated atthe connection between the thermocouple andterminal of your data acquisition device.

CJC improves your measurement accuracy by providingthe temperature at this junction and applying the

appropriate correction.

C i l diti i f


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Common signal conditioning for

different sensors


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Bridge Completion

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Embedded Systemasds Lecture