DOC B2.Pwmpulsegeneration

7/30/2019 DOC B2.Pwmpulsegeneration

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GOKARAJU RANGARAJU INSTITUTE OFENGINEERING AND TECHNOLOGY

Hyderabad, Andhra Pradesh.

DEPARTMENT OF ELECTRICAL AND ELECTRONICSENGINEERING


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GENERATION OF PULSE WIDTH

MODULATION SIGNALS USINGSINUSOIDAL WAVE FORM

By :

B.RAJASEKAR RAJU

G.SAI KRISHNA

M.SAI KUMAR

P.SURESH

L.VAMSI KRISHNA


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CONTENTS

TOPIC PAGE NO.

Abstract i

1. Introduction 01

1.1 Objective1.2 What is pwm?1.3 Introductio

2. Block Diagram & Description 05

2.1 Block Diagram

2.2 Description of Block Diagram

3. Hardware Design 09

3.1 Microcontroller AT89C51

3.2 CRO

4. Software Design 26


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4.1 Proteus design.

5. Source code 27

Topic Page no.

6 Applications 28

6.1 Application

7. References 29


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ABSTRACT :

This paper presents the generation of pulse width modulation (PWM) by using

MICROCONTROLLER (8051).In this the sinusoidal wave is generated by and is compared with

the saw tooth wave. These wave forms are compared to generate required pulse width

modulation signal (PWM).Pulse width modulation (PWM) is a very efficient way of providingintermediate amounts of electrical power between fully on an fully off. a simple power switch

with a typical power source provides full power only when switched on. The term duty cycle

describes the proportion of on time to the regular interval or period of time a low duty cycle

corresponds to low power , because the power is off for most of the time. duty cycle is expressed

in percent,100% being fully on.PWM works well with digital controls ,which, because of theiron/off nature , can easily set the needed duty cycle.PWM of a signal or power source involves

the modulation of its duty cycle ,to either convey information over a communication channel or

control the amount of power sent to a load.

Pulse Width Modulation, abbreviated as PWM, is a method of transmitting information on a

series of pulses. The data that is being transmitted is encoded on the width of these pulses to

control the amount of power being sent to a load. In other words, pulse width modulation is a

modulation technique for generating variable width pulses to represent the amplitude of an input

analog signal or wave. The popular applications of pulse width modulation are in power delivery,

voltage regulation and amplification and audio effects.


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i

Chapter 1: INTRODUCTION

1.1Objective :

Generating PWM pulses using MICROCONTROLLER (8051).

1.2What is pwm?

(Pulse Width Modulation) A modulation technique that uses a digital circuit to create a

variable analog signal. PWM is a simple concept: open and close a switch at uniform, repeatable

intervals. Analog circuits that vary the voltage tend to drift, and it costs more to produce ones

that do not than it does to make digital PWM circuits. In addition, control of almost everything

today is already in the digital realm. For example, PWM is widely used to control the speed of a

DC motor and the brightness of a bulb, in which case the PWM circuit is used to open/close a

power line. If the line were opened for 1ms and closed for 1ms, and this were continuously

repeated, the target would receive an average of 50% of the voltage and run at half speed or half

brightness. If the line were opened for 1ms and closed for 3ms, the target would receive an

average of 25%. Today, PWM technique has been used in wide applications, such voltage

control, current control, motor control, power control, UPS, inverter etc.,.

1.3Introduction:


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Pulse width modulation (PWM) is a very efficient way of providing

intermediate amounts of electrical power between fully on an fully off. a simple power

switch with a typical power source provides full power only when switched on.PWM is

comparatively recent technique ,made practical by modern electronic power switches

although one of its applications was in Sinclair x10,a 10 W audio amplifier available in

kit form in 1960s.

1

Fig 1.1

In the past, when only partial power is needed (such as sewing machine motor),a

rheostat (located in the sewing machine foot pedal ) connected in series with the motor adjusted

the amount of the current flowing through the motor, but also wasted power as heat in theresistor element. It was an insufficient scheme, but tolerable because the total power is low.this

was one of the several methods of controlling power. There were otherssome stil in usesuch

as variable autotransformers, including the trade nmarked autrastat for theoretical lighting and

the variac,for general power adjustment. These were quite efficient, but also relatively costly.


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For about a century , some variables-speed electric motors have had decent efficiency,

but there was some what more complex than constant-speed motor, and some times required

external electrical apparatus, such as a bankof variable power resistors.

However there is a great need for applying partial power in other devices, such as

electric stoves,lamp dimmers and robotic servos.basically, a PWM variable-power schemeswitches the power quickly between fully on and fully off. In any event, the switching rate is

much faster than what would effect theload, which is tosay the device that uses the power. In

practice, applying full power for part of the time doesnnot cause any problems;PWM is practical.

2

The term duty cycle describes the proportion of on time to the regular interval or

period of time a low duty cycle corresponds to low power , because the power is off for most of

the time. duty cycle is expressed in percent,100% being fully on.

PWM works well with digital controls ,which, because of their on/off nature , can

easily set the needed duty cycle.

PWM of a signal or power source involves the modulation of its duty cycle ,to either

convey information over a communication channel or control the amount of power sent to a load.


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Fig 1.2

Pulse width modulation is used to reduce the total power delivered to a load without

resulting in loss, which normally occurs when a power source is limited by a resistive element.

The underlying principle in the whole process is that the average power delivered is directly

proportional to the modulation duty cycle. If the modulation rate is high, it is possible to smoothout the pulse train using passive electronic filters and recover an average analog wave form.

Multi-phase machines and drives is a topic of growing relevance in recent years, and it

presents many challenging issues that still need further research. This is the case of multi-phase

3

space vector pulse width modulation (SVPWM), which shows not only more space vectors thanthe standard three-phase case, but also new subspaces where the space vectors are mapped.

Different approaches have been recently followed, and the aim of this paper is to review and

classify these methods. Comparative results are included to highlight the weak and strong points

of the different methods. Finally some conclusions are extracted pointing out the problems thatstill need to be solved.


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Chapter 2: Block Diagram & Description

2.1 Block Diagram :

GENERATION OF PMW SIGNALS USING 89C51 IN PROTEUS

SOFTWARE:

SCHEMATIC:


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Fig 2.1

5

Output waveform


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Fig 2.2

2.2 Description of Block Diagram

Figure 2.1 shows the schematic diagram.

C program is writtensuch that the sine wave and ramp wave are compared to each othersuch that PWM pulses are produced.

Initially the source code should be written on notepad.

This code should be verified for any warning and error instructions and this error lessprogram should be used to create HEX file in KIEL.

This HEX file is dumpedin to the 89C51 in PROTEUS software where we designed theschematic as shown the figure.


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External clock signal must be give to the 89c51 microcontroller using crystal oscillatorand also capacitors as shown in the figure.

As the program is written in such a way that the output signals(pwm) obtained aftercomparing sine wave with ramp signal is assigned to pin1 of port1,the oscilloscope is

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connected to the pin1 of port1.

Figure2.2 shows the output pulse width modulation signals.

GENERATION OF PMW SIGNALS USING MATLAB

Fig 2.3

Description:


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We can also generate pwm signals using matlab software.

Above block diagram consists of the following:1. Sinewave generator2. Signal generator in which sawtooth wave form is selected.3. Relational operator4. Scope

7

Relational operator compares the two input signals(i.e.,sinewave and sawtooth) whichare given to the two input terminals of relational operator.

The function of relational operator is, when the magnitude of sinewave is greater than thesawtooth wave a pulse is generated and when the magnitude of sine is less than the

sawtooth wave ,the magnitude of the pulse will be zero.


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Chapter 3: Hardware Design

Microcontroller

Definition :

An embedded microcontroller is chip which has a computer processor with all its support

functions (clock & reset), memory (both program and data), and I/O(including bus interface)

built in to the device. These built in function minimize the need for external circuits and devices

to be designed in the final application.

Types of Microcontroller:

Creating application for microcontrollers is completely different than any other development

job in computing and electronics. In most other application one probably have a number of

subsystems and interface already available for his/her use. This is not the case with a

microcontroller where one is responsible for-


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Power distribution System clocking Interface design and wiring System programming Application programming Device programming

Before selecting a particular device for an application, its important to understand what thedifferent option and features are and what they can mean with regard to developing application.

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Embedded Microcontroller

When all the hardware required to run the application is provided on the chip, it is

refer to as an embedded microcontroller. All that is typically required to operate the

device is power, reset, and a clock. Digital I/O pins are provided to allow interfacing with

external devices.

External Memory Microcontroller


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Sometimes, the program memory is insufficient for an application or , during

debug; a separate ROM(or even RAM) would make the work easier. Some

microcontrollers including the 8051 allow the connection of external memory.

An external memory microcontroller seems to primarily differ from a

microprocessor in the areas of built in peripheral features. These features could include

memory device selection (avoiding the need for external address decoders or DRAM

address multiplexers), timers, interrupt controllers, DMA, and I/O devices like serial

ports.

Features of AT89C51

Compatible with MCS-51 Products. 4K Bytes of In-System Reprogrammable

Flash Memory.Endurance: 1,000 Write/Erase Cycles.

Fully Static Operation: 0 Hz to 24 MHz. Three-level Program Memory Lock. 128 x 8-bit Internal RAM. 32 Programmable I/O Lines. Two 16-bit Timer/Counters. Six Interrupt Sources. Programmable Serial Channel.

10

Low-power Idle and Power-down Modes


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Description:

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K

bytes of Flash programmable and erasable read only memory (PEROM). The device

is manufactured using Atmels high-density non-volatile memory technology and is

compatible with the industry-standard MCS-51 instruction set and pin out. The on-chip

flash allows the program memory to be reprogrammed in-system or by a conventional

non-volatile memory programmer. By combining a versatile 8-bit CPU with Flash on a

monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a

highly-flexible and cost-effective solution to many embedded control applications


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PIN DIAGRAM OF 8051


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Fig 3.1

12


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BLOCK DIAGRAM

fig 3.2

13


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Fig 3.3

Pin Description

VCC

Supply voltage.

GND

Ground.

Port 0

Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight

TTL inputs. When 1s are written to port 0 pins, the pins can be used as highimpedance inputs.

Port 0 may also be configured to be the multiplexed loworder address/data bus during accesses to


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external program and data memory. In this mode P0 has internal pullups. Port 0 also receives the

code bytes during Flash programming, and outputs the code bytes during program verification.

External pullups are required during program verification.

Port 1

Port 1 is an 8-bit bi-directional I/O port with internal pullups.The Port 1 output buffers can

sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the

internal pullups and can be used as inputs. As inputs,Port 1 pins that are externally being pulled

low will source current (IIL) because of the internal pullups. Port 1 also receives the low-order

address bytes during Flash programming and verification.

Port 2


sink/source four TTL inputs.When 1s are written to Port 2 pins they are pulled high by the

internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled

low will source current (IIL) because of the internal pullups. Port 2 emits the high-order address

byte during fetches from external program memory and during accesses to external data memory

that use 16-bit addresses (MOVX @ DPTR). In this application, it uses strong internal pull-ups

when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @

RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-

order address bits and some control signals during Flash programming and verification.

Port 3


sink/source four TTL inputs.When 1s are written to Port 3 pins they are pulled high by the

internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled

low will source current (IIL) because of the pullups. Port 3 also serves the functions of various

special features of the AT89C51 as listed below:


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Port 3 also receives some control signals for Flash programming and verification.

RST

Reset input. A high on this pin for two machine cycles while the oscillator is running resets

the device.

ALE/PROG

Address Latch Enable output pulse for latching the low byte of the address during accesses to

external memory. This pin is also the program pulse input (PROG) during Flash programming.In

normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be

used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped

during each access to external Data Memory. If desired, ALE operation can be disabled by

setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or

MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no

effect if the microcontroller is in external execution mode.


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PSEN

Program Store Enable is the read strobe to external program memory. When the AT89C51 is

executing code from external program memory, PSEN is activated twice each machine cycle,

except that two PSEN activations are skipped during each access to external data memory.

EA/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to fetch

code from external program memory locations starting at 0000H up to FFFFH. Note, however,

that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to

VCC for internal program executions. This pin also receives the 12-volt programming enable

voltage (VPP) during Flash programming, for parts that require 12-volt VPP.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier.

Oscillator Characteristics

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can

be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz crystal or

ceramic resonator may be used. To drive the device from an external clock source, XTAL2 hould

be left unconnected while XTAL1 is driven as shown in Figure 2. There are no requirements on

the duty cycle of the external clock signal, since the input to the internal clocking circuitry is

through a divide-by-two flip-flop, but minimum and maximum voltage high and low time

specifications must be observed.


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OSCILLATOR CONNECTIONS

Fig 3.4


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External Clock Drive Configuration

Fig 3.5

Idle Mode

In idle mode, the CPU puts itself to sleep while all the onchip peripherals remain active. The

mode is invoked by software. The content of the on-chip RAM and all the special functions

registers remain unchanged during this mode. The idle mode can be terminated by any enabled

interrupt or by a hardware reset. It should be noted that when idle is terminated by a hard ware

reset, the device normally resumes program execution, rom where it left off, up to two machine


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cycles beforethe internal reset algorithm takes control. On-chip hardware inhibits access to

internal RAM in this event, but access to the port pins is not inhibited. To eliminate the

possibility of an unexpected write to a port pin when Idle is terminated by reset, the instruction

following the one that invokes Idle should not be one that writes to a port pin or to external

memory.

Power-down Mode

In the power-down mode, the oscillator is stopped, and theinstruction that invokes power

down is the last instruction executed. The on-chip RAM and Special Function Registers retain

their values until the power-down mode is terminated. The only exit from power-down is a

hardware reset. Reset redefines the SFRs but does not change the on-chip RAM. The reset

should not be activated before VCC is restored to its normal operating level and must be held

active long enough to allow the oscillator to restart and stabilize.

Status of External Pins During Idle and Power-down Modes

Table 3.1

Program Memory Lock Bits

On the chip are three lock bits which can be left unprogrammed(U) or can be programmed (P)

to obtain the additional features listed in the table below. When lock bit 1 is programmed, the

logic level at the EA pin is sampled and latched during reset. If the device is powered up without

a reset, the latch initializes to a random value, and holds that value until reset is activated. It is


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necessary that the latched value of EA be in agreement with the current logic level at that pin in

order for the device to function properly.

Lock Bit Protection Modes

Table 3.2

Programming Algorithm:

Before programming the AT89C51, the address, data and control signals should be set up

according to the Flash programming mode table and Figure 3 and Figure 4. To program the

AT89C51, take the following steps.

1. Input the desired memory location on the address lines.

2. Input the appropriate data byte on the data lines.

3. Activate the correct combination of control signals.

4. Raise EA/VPP to 12V for the high-voltage programming mode.

5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The byte-write


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cycle is self-timed and typically takes no more than 1.5 ms.

Repeat steps 1 through 5, changing the addressand data for the entire array or until the end of theobject file is reached.

Data Polling:

The AT89C51 features Data Polling to indicate the end of a write cycle. During a write cycle,

an attempted read of the last byte written will result in the complement of the written datum on

PO.7. Once the write cycle has been completed, true data are valid on all outputs, and the next

cycle may begin. Data Polling may begin any time after a write cycle has been initiated.

Ready/Busy:

The progress of byte programming can also be monitored by the RDY/BSY output signal.

P3.4 is pulled low after ALE goes high during programming to indicate BUSY. P3.4 is pulled

high again when programming is done to indicate READY.

Program Verify:

If lock bits LB1 and LB2 have not been programmed, the programmed code data can be read

back via the address and data lines for verification. The lock bits cannot be verified directly.

Verification of the lock bits is achieved by observing that their features are enabled.

Chip Erase:

The entire Flash array is erased electrically by using the proper combination of control

signals and by holding ALE/PROG low for 10 ms. The code array is written with all 1s. The

chip erase operation must be executed before the code memory can be re-programmed.

Reading the Signature Bytes:

The signature bytes are read by the same procedure as a normal verification of

locations 030H, 031H, and 032H, except that P3.6 and P3.7 must be pulled to a logic low. The

values returned are as follows.


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(030H) = 1EH indicates manufactured by Atmel

(031H) = 51H indicates 89C51

(032H) = FFH indicates 12V programming

(032H) = 05H indicates 5V programming

Programming Interface

Every code byte in the Flash array can be written and the entire array can be erased by using

the appropriate combination of control signals. The write operation cycle is selftimed

and once initiated, will automatically time itself to completion. All major programming vendors

offer worldwide support for the Atmel microcontroller series. Please contact your local

programming vendor for the appropriate software revision.

3.2 CRO:

Cathode-Ray Oscilloscope

INTRODUCTION:

The cathode ray oscilloscope(CRO) is a common laboratory instrument that provides accuratetime and altitude measurements of voltage signals over a wide range of frequencies. Its

reliability,stability and ease of operation make it suitable as a general purpose laboratory

instrument.the heart of the CRO is a cathode ray tube shown in figure 3.6.


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Fig 3.6

The cathode ray is a beam of electrons which are emitted by the heated cathode (negative

electrode) and accelerated toward the fluorescent screen. The assembly of the cathode, intensitygrid, focus grid, and accelerating anode (positive electrode) is called an electron gun. Its purpose

is to generate the electron beam and control its intensity and focus. Between the electron gun andthe fluorescent screen are two pair of metal plates - one oriented to provide horizontal deflectionof the beam and one pair oriented ot give vertical deflection to the beam. These plates are thus

referred to as the horizontal andvertical deflection plates. The combination of these two

deflections allows the beam to reach any portion of the fluorescent screen. Wherever the electronbeam hits the screen, the phosphor is excited and light is emitted from that point. This coversion

of electron energy into light allows us to write with points or lines of light on an otherwise

darkened screen.

In the most common use of the oscilloscope the signal to be studied is first amplified and

then applied to the vertical (deflection) plates to deflect the beam vertically and at the same time

a voltage that increases linearly with time is applied to the horizontal (deflection) plates thuscausing the beam to be deflected horizontally at a uniform (constant> rate. The signal applied to

the verical plates is thus displayed on the screen as a function of time. The horizontal axis serves

as a uniform time scale

CRO Operation:

A simplified block diagram of a typical oscilloscope is shown in Fig. 3. In general, the


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instrument is operated in the following manner. The signal to be displayed is amplified by thevertical amplifier and applied to the verical deflection plates of the CRT. A portion of the signal

in the vertical amplifier is applied to the sweep trigger as a triggering signal. The sweep trigger

then generates a pulse coincident with a selected point in the cycle of the triggering signal. Thispulse turns on the sweep generator, initiating the sawtooth wave form. The sawtooth wave isamplified by the horizontal amplifier and applied to the horizontal deflection plates. Usually,

additional provisions signal are made for appliying an external triggering signal or utilizing the

60 Hz line for triggering. Also the sweep generator may be bypassed and an external signal

applied directly to the horizontal amplifier.

CRO controls:

The controls available on most oscilloscopes provide a wide range of operating conditions and

thus make the instrument especially versatile. Since many of these controls are common to most

oscilloscopes a brief description of them follows.

Block diagram of typical oscilloscope

Fig 3.7


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Chapter 4: Software design

4.1Proteus design:

26


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Chapter 5: Source code in c-language

#include#includesbit pulse=P1^0;voidmain(){inti,j,x,f=50;for(i=0;ij)pulse=1;elsepulse=0;}}

27


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Chapter 6: Applications

7.1 APPLICATIONS:

Three Phase Induction Motor Speed Controllers. Uninterruptible Power Supplies. Static Inverter Power Supplies. Power Waveform Generators. Speed control of ID fans.


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Chapter 7: Bibliography

REFERENCE BOOKS:

Programming in ANSI C: E BALAGURUSAMY. The 8051microcontroller and embedded systems: MUHAMMAD ALI MAZIDI.

JANICE GILLISPIE MAZIDI.

The 8051 microcontroller: KENNETH J. AYALA.

WEB SITES: www.atmel.com www.national.com www.google.com www.scientech.bz
http://www.atmel.com/http://www.national.com/http://www.google.com/http://www.scientech.bz/http://www.scientech.bz/http://www.google.com/http://www.national.com/http://www.atmel.com/


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