INTRODUCTION

1.1 EMBEDDED SYSTEMS:

An embedded system is a special-purpose system in which the computer is

completely encapsulated by or dedicated to the device or system it controls.

Unlike a general-purpose computer, such as a personal computer, an embedded

system performs one or a few predefined tasks, usually with very specific

requirements. Since the system is dedicated to specific tasks, design engineers can

optimize it, reducing the size and cost of the product. Embedded systems are often

mass-produced, benefiting from economies of scale.

Personal digital assistants (PDAs) or handheld

computers are generally considered embedded

devices because of the nature of their hardware

design, even though they are more expandable in

software terms. This line of definition continues to

blur as devices expand. With the introduction of the

OQO Model 2 with the Windows XP operating

system and ports such as a USB port — both features usually belong to "general

purpose computers", — the line of nomenclature blurs even more.

Embedded systems plays major role in electronics varies from portable

devices to large stationary installations like digital watches and MP3 players,

traffic lights, factory controllers, or the systems controlling nuclear power plants.

In terms of complexity embedded systems can range from very simple with

a single microcontroller chip, to very complex with multiple units, peripherals and

networks mounted inside a large chassis or enclosure.

Examples of Embedded Systems:

Avionics, such as inertial guidance systems, flight control

hardware/software and other integrated systems in aircraft and missiles

Cellular telephones and telephone switches

Engine controllers and antilock brake controllers for automobiles

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Home automation products, such as thermostats, air conditioners,

sprinklers, and security monitoring systems

Handheld calculators

Handheld computers

Household appliances, including microwave ovens, washing machines,

television sets, DVD players and recorders

Medical equipment

Personal digital assistant

Videogame consoles

Computer peripherals such as routers and printers.

Industrial controllers for remote machine operation.

1.2. INTRODUCTION TO THE PROJECT:

The project uses the standard concept of Ohms law i.e., when a low DC voltage is

applied at the feeder end through a series resistor (Cable lines), then current would vary

depending upon the location of fault in the cable. In case there is a short circuit (Line to

Ground), the voltage across series resistors changes accordingly, which is then fed to an

ADC to develop precise digital data which the programmed microcontroller of 8051

family would display in kilometers.

The project is assembled with a set of resistors representing cable length in KM’s

and fault creation is made by a set of switches at every known KM to cross check the

accuracy of the same. The fault occurring at a particular distance and the respective

phase is displayed on a LCD interfaced to the microcontroller.

GSM module is used to send a sms to the sub-station about phase fault and

distance calculated.

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BLOCK DIAGRAM:

BLOCK DIAGRAM:

LCD display: Normal. Abnormal condition.

3 Phases should be there and each phase 4 switches. (Each switch 2KM)

GSM to send the msg regarding distance and fault phase

1.3. BLOCK DIAGRAM DESCRIPTION:

Power Supply: This section is meant for supplying Power to all the sections

mentioned above. It basically consists of a Transformer to step down the 230V ac

to 9V ac followed by diodes. Here diodes are used to rectify the ac to dc. After

rectification the obtained rippled dc is filtered using a capacitor Filter. A positive

voltage regulator is used to regulate the obtained dc voltage.

Microcontroller: This section forms the control unit of the whole project. This

section basically consists of a Microcontroller with its associated circuitry like

Crystal with capacitors, Reset circuitry, Pull up resistors (if needed) and so on.

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MICRO CONTROLLER

8051

POWER

SUPPLY

VOLTAGE SENSING CIRCUIT

Relay

Fault switches

LCD(16x2)

GSM

R:NF Y:NF B:NF

Distance: 000KM

R:NF Y:F B:NF

Distance: 002KM

The Microcontroller forms the heart of the project because it controls the devices

being interfaced and communicates with the devices according to the program

being written.

LCD Display: This section is basically meant to show up the status of the project.

This project makes use of Liquid Crystal Display to display / prompt for

necessary information.

Relay Section: This section consists of an interfacing circuitry to switch ON /

OFF the system whenever any unhealthy conditions i.e. overload is detected. This

circuitry basically consists of a Relay, transistor and a protection diode. A relay is

used to drive the 230V devices.

SCHEMATIC:

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SCHEMATIC DESCRIPTION:

Firstly, the required operating voltage for Microcontroller AT89S52 is 5V. Hence

the 5V D.C. power supply is needed by the same. This regulated 5V is generated by first

stepping down the 230V to 18V by the step down transformer.

In the both the Power supplies the step downed a.c. voltage is being rectified by

the Bridge Rectifier. The diodes used are 1N4007. The rectified a.c voltage is now

filtered using a ‘C’ filter. Now the rectified, filtered D.C. voltage is fed to the Voltage

Regulator. This voltage regulator allows us to have a Regulated Voltage. In Power

supply given to Microcontroller 5V is generated using 7805 and in other two power

supply 12V is generated using 7812. The rectified; filtered and regulated voltage is again

filtered for ripples using an electrolytic capacitor 100μF. Now the output from the first

section is fed to 40th pin of AT89S52 microcontroller to supply operating voltage and

from other power supply to circuitry.

The microcontroller AT89S52 with Pull up resistors at Port0 and crystal

oscillator of 11.0592 MHz crystal in conjunction with couple of capacitors of is placed

at 18th & 19th pins of AT89S52 to make it work (execute) properly.

CIRCUIT DESCRIPTION:

DESCRIPTION:

The project uses the standard concept of Ohms law i.e., when a low DC voltage is

applied at the feeder end through a series resistor (Cable lines), then current would vary

depending upon the location of fault in the cable. In case there is a short circuit (Line to

Ground), the voltage across series resistors changes accordingly, which is then fed to an

ADC to develop precise digital data which the programmed microcontroller of 8051

family would display in kilometers.

The project is assembled with a set of resistors representing cable length in KM’s

and fault creation is made by a set of switches at every known KM to cross check the

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accuracy of the same. The fault occurring at a particular distance and the respective

phase is displayed on a LCD interfaced to the microcontroller.

GSM module is used to send a sms to the sub-station about phase fault and

distance calculated.

HARDWARE REQUIRED:

Microcontroller

LCD

Switches

Power supply

Voltage sensing circuit

Relay

GSM

SOFTWARE TOOLS:

1. Embedded C

2. Keil Uvision3

3. Uc-Flash or ISP

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HARD WARE EXPLANATION:

MICRO CONTROLLER 89C51

Introduction

A Micro controller consists of a powerful CPU tightly coupled with

memory, various I/O interfaces such as serial port, parallel port timer or counter,

interrupt controller, data acquisition interfaces-Analog to Digital converter,

Digital to Analog converter, integrated on to a single silicon chip.

If a system is developed with a microprocessor, the designer has to go for

external memory such as RAM, ROM, EPROM and peripherals. But controller is

provided all these facilities on a single chip. Development of a Micro controller

reduces PCB size and cost of design.

One of the major differences between a Microprocessor and a Micro controller is

that a controller often deals with bits not bytes as in the real world application.

Intel has introduced a family of Micro controllers called the MCS-51.

The Major Features:

Compatible with MCS-51 products

4k Bytes of in-system Reprogrammable flash memory

Fully static operation: 0HZ to 24MHZ

Three level programmable clock

128 * 8 –bit timer/counters

Six interrupt sources

Programmable serial channel

Low power idle power-down modes

Why AT 89C51

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The system requirements and control specifications clearly rule out the use

of 16, 32 or 64 bit micro controllers or microprocessors. Systems using these may

be earlier to implement due to large number of internal features. They are also

faster and more reliable but, 8-bit micro controller satisfactorily serves the above

application. Using an inexpensive 8-bit Microcontroller will doom the 32-bit

product failure in any competitive market place.

Coming to the question of why to use AT89C51 of all the 8-bit

microcontroller available in the market the main answer would be because it has 4

Kb on chip flash memory which is just sufficient for our application. The on-chip

Flash ROM allows the program memory to be reprogrammed in system or by

conventional non-volatile memory Programmer. Moreover ATMEL is the leader

in flash technology in today’s market place and hence using AT 89C51 is the

optimal solution.

AT89C51 MICROCONTROLLER ARCHITECTURE

The 89C51 architecture consists of these specific features:

Eight –bit CPU with registers A (the accumulator) and B

Sixteen-bit program counter (PC) and data pointer (DPTR)

Eight- bit stack pointer (PSW)

Eight-bit stack pointer (Sp)

Internal ROM or EPROM (8751) of 0(8031) to 4K (89C51)

Internal RAM of 128 bytes:

1. Four register banks, each containing eight registers

2. Sixteen bytes, which maybe addressed at the bit level

3. Eighty bytes of general- purpose data memory

Thirty –two input/output pins arranged as four 8-bit ports:p0-p3

Two 16-bit timer/counters: T0 and T1

Full duplex serial data receiver/transmitter: SBUF

Control registers: TCON, TMOD, SCON, PCON, IP, and IE

Two external and three internal interrupts sources.

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Oscillator and clock circuits.

Functional block diagram of micro controller

The 89C51 oscillator and clock:

The heart of the 89C51 circuitry that generates the clock pulses by which

all the internal all internal operations are synchronized. Pins XTAL1 And XTAL2

is provided for connecting a resonant network to form an oscillator. Typically a

quartz crystal and capacitors are employed. The crystal frequency is the basic

internal clock frequency of the microcontroller. The manufacturers make 89C51

designs that run at specific minimum and maximum frequencies typically 1 to 16

MHz.

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Fig 3.7.2: - Oscillator and timing circuit

Types of memory:

The 89C51 have three general types of memory. They are on-chip memory,

external Code memory and external Ram. On-Chip memory refers to physically

existing memory on the micro controller itself. External code memory is the code

memory that resides off chip. This is often in the form of an external EPROM.

External RAM is the Ram that resides off chip. This often is in the form of

standard static RAM or flash RAM.

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a) Code memory

Code memory is the memory that holds the actual 89C51 programs that is

to be run. This memory is limited to 64K. Code memory may be found on-chip or

off-chip. It is possible to have 4K of code memory on-chip and 60K off chip

memory simultaneously. If only off-chip memory is available then there can be

64K of off chip ROM. This is controlled by pin provided as EA

b) Internal RAM

The 89C51 have a bank of 128 of internal RAM. The internal RAM is

found on-chip. So it is the fastest Ram available. And also it is most flexible in

terms of reading and writing. Internal Ram is volatile, so when 89C51 is reset, this

memory is cleared. 128 bytes of internal memory are subdivided. The first 32

bytes are divided into 4 register banks. Each bank contains 8 registers. Internal

RAM also contains 128 bits, which are addressed from 20h to 2Fh. These bits are

bit addressed i.e. each individual bit of a byte can be addressed by the user. They

are numbered 00h to 7Fh. The user may make use of these variables with

commands such as SETB and CLR.

FLASH MEMORY:

Flash memory (sometimes called "flash RAM") is a type of constantly-

powered non volatile that can be erased and reprogrammed in units of memory

called blocks. It is a variation of electrically erasable programmable read-only

memory (EEPROM) which, unlike flash memory, is erased and rewritten at the

byte level, which is slower than flash memory updating. Flash memory is often

used to hold control code such as the basic input/output system (BIOS) in a

personal computer. When BIOS needs to be changed (rewritten), the flash

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memory can be written to in block (rather than byte) sizes, making it easy to

update. On the other hand, flash memory is not useful as random access memory

(RAM) because RAM needs to be addressable at the byte (not the block) level.

Flash memory gets its name because the microchip is organized so that a

section of memory cells are erased in a single action or "flash." The erasure is

caused by Fowler-Nordheim tunneling in which electrons pierce through a thin

dielectric material to remove an electronic charge from a floating gate associated

with each memory cell. Intel offers a form of flash memory that holds two bits

(rather than one) in each memory cell, thus doubling the capacity of memory

without a corresponding increase in price.

Flash memory is used in digital cellular phones, digital cameras, LAN

switches, PC Cards for notebook computers, digital set-up boxes, embedded

controllers, and other devices.

Memory Type

Features

FLASH Low-cost, high-density, high-speed

architecture; low power; high

reliability

ROM

Read-Only Memory

Mature, high-density, reliable, low

cost; time-consuming mask required,

suitable for high production with

stable code

SRAM

Static Random-Access Memory

Highest speed, high-power, low-

density memory; limited density

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drives up cost

EPROM

Electrically Programmable Read-

Only Memory

High-density memory; must be

exposed to ultraviolet light for

erasure

EEPROMorE2PROM

Electrically Erasable Programmable

Read-Only Memory

Electrically byte-erasable; lower

reliability, higher cost, lowest density

DRAM

Dynamic Random Access Memory

High-density, low-cost, high-speed,

high-power

Technical Overview of Flash Memory

Flash memory is a nonvolatile memory using NOR technology, which allows the

user to electrically program and erase information. Intel® Flash memory uses

memory cells similar to an EPROM, but with a much thinner, precisely grown

oxide between the floating gate and the source (see Figure 2). Flash programming

occurs when electrons are placed on the floating gate. The charge is stored on the

floating gate, with the oxide layer allowing the cell to be electrically erased

through the source. Intel Flash memory is an extremely reliable nonvolatile

memory architecture.

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Fig 3.7.3: - Pin diagram of AT89C51

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 one’s are written to port 0 pins, the pins can

be used as high impedance inputs. Port 0 may also be configured to be the

multiplexed low order address/data bus during accesses to external program and

data memory. In this mode P0 has internal pull-ups. Port 0 also receives the code

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

verification. External pull-ups are required during program verification.

Port 1:

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. 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 pull-ups 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 pull-ups. Port 1 also receives the low-order address bytes during

Flash programming and verification.

Port 2:

Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2

output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins

they are pulled high by the internal pull-ups 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 pull-ups. Port 2 emits the high-order address byte during fetches

from external program memory and during accesses to external data memories

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

internal pull-ups when emitting 1s. During accesses to external data memories 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:

Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3

output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins

they are pulled high by the internal pull-ups and can be used as inputs. As inputs,

Port 3 pins that are externally being pulled low will source current (IIL) because

of the pull-ups.

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Port 3 also serves the functions of various special features of the AT89C51 as

listed below:

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

Tab 6.2.1 Port pins and their alternate functions

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 1/6the 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 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:

It is the 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

Figs 6.2.3. Either a quartz crystal or ceramic resonator may be used. To drive the

device from an external clock source, XTAL2 should be left unconnected while

XTAL1 is driven as shown in Figure 6.2.4.There are no requirements on the duty

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

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

low time specifications must be observed.

Fig 6.2.3 Oscillator Connections Fig 6.2.4 External Clock Drive

Configuration

Notes:

1. Under steady state (non-transient) conditions, IOL must be externally

limited as follows:

Maximum IOL per port pin: 10 mA

Maximum IOL per 8-bit port: Port 0: 26 mA

Ports 1, 2, 3: 15 mA

Maximum total IOL for all output pins: 71 mA

If IOL exceeds the test condition, VOL may exceed the related

specification. Pins are not guaranteed to sink current greater than the

listed test conditions.

2. Minimum VCC for Power-down is 2V.

REGISTERS:

In the CPU, registers are used to store information temporarily. That

information could be a byte of data to be processed, or an address pointing to the

data to be fetched. The vast majority of 8051 registers are 8–bit registers. In the

8051 there is only one data type: 8bits. The 8bits of a register are shown in the

diagram from the MSB (most significant bit) D7 to the LSB (least significant bit)

D0. With an 8-bit data type, any data larger than 8bits must be broken into 8-bit

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chunks before it is processed. Since there are a large number of registers in the

8051, we will concentrate on some of the widely used general-purpose registers

and cover special registers in future chapters.

D7 D6 D5 D4 D3 D2 D1 D0

The most widely used registers of the 8051 are A (accumulator), B, R0,

R1, R2, R3, R4, R5, R6, R7, DPTR (data pointer), and PC (program counter). All

of the above registers are 8-bits, except DPTR and the program counter. The

accumulator, register A, is used for all arithmetic and logic instructions.

SFRs (Special Function Registers)

Among the registers R0-R7 is part of the 128 bytes of RAM memory.

What about registers A, B, PSW, and DPTR? Do they also have addresses? The

answer is yes. In the 8051, registers A, B, PSW and DPTR are part of the group

of registers commonly referred to as SFR (special function registers). There are

many special function registers and they are widely used. The SFR can be

accessed by the names (which is much easier) or by their addresses. For example,

register A has address E0h, and register B has been ignited the address F0H, as

shown in table.

The following two points should noted about the SFR addresses.

1. The Special function registers have addresses between 80H and FFH.

These addresses are above 80H, since the addresses 00 to 7FH are

addresses of RAM memory inside the 8051.

2. Not all the address space of 80H to FFH is used by the SFR. The

unused locations 80H to FFH are reserved and must not be used by the

8051 programmer.

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Regarding direct addressing mode, notice the following two points: (a) the

address value is limited to one byte, 00-FFH, which means this addressing mode

is limited to accessing RAM locations and registers located inside the 8051. (b) If

you examine the l st file for an assembly language program, you will see that the SFR

registers names are replaced with their addresses as listed in table.

Symbol Name Address

ACC Accumulator 0E0H

B B register 0F0H

PSW Program status word 0D0H

SP Stack pointer 81H

DPTR Data pointer 2 bytes

DPL Low byte 82H

DPH High byte 83H

P0 Port0 80H

P1 Port1 90H

P2 Port2 0A0H

P3 Port3 0B0H

IP Interrupt priority control 0B8H

IE Interrupt enable control 0A8H

TMOD Timer/counter mode control 89H

TCON Timer/counter control 88H

T2CON Timer/counter 2 control 0C8H

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T2MOD Timer/counter mode2 control 0C9H

TH0 Timer/counter 0high byte 8CH

TL0 Timer/counter 0 low byte 8AH

TH1 Timer/counter 1 high byte 8DH

TL1 Timer/counter 1 low byte 8BH

TH2 Timer/counter 2 high byte 0CDH

TL2 Timer/counter 2 low byte 0CCH

RCAP2H T/C 2 capture register high byte 0CBH

RCAP2L T/C 2 capture register low byte 0CAH

SCON Serial control 98H

SBUF Serial data buffer 99H

PCON Power control 87H

Table: 8051 Special function register Address

A Register (Accumulator)

This is a general-purpose register which serves for storing intermediate results

during operating. A number (an operand) should be added to the accumulator

prior to execute an instruction upon it. Once an arithmetical operation is

preformed by the ALU, the result is placed into the accumulator. If a data should

be transferred from one register to another, it must go through accumulator. For

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such universal purpose, this is the most commonly used register that none

microcontroller can be imagined without (more than a half 8051 microcontroller's

instructions used use the accumulator in some way).

B Register

B register is used during multiply and divide operations which can be performed

only upon numbers stored in the A and B registers. All other instructions in the

program can use this register as a spare accumulator (A).

During programming, each of registers is called by name so that

their exact address is not so important for the user. During compiling into machine

code (series of hexadecimal numbers recognized as instructions by the

microcontroller), PC will automatically, instead of registers’ name, write

necessary addresses into the microcontroller.

R Registers (R0-R7)

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This is a common name for the total 8 general purpose registers (R0, R1, and

R2 ...R7). Even they are not true SFRs; they deserve to be discussed here because

of their purpose. The bank is active when the R registers it includes are in use.

Similar to the accumulator, they are used for temporary storing variables and

intermediate results. Which of the banks will be active depends on two bits

included in the PSW Register. These registers are stored in four banks in the

scope of RAM.

The following example best illustrates the useful purpose of these registers.

Suppose that mathematical operations on numbers previously stored in the R

registers should be performed: (R1+R2) - (R3+R4). Obviously, a register for

temporary storing results of addition is needed. Everything is quite simple and the

program is as follows:

MOV A, R3; Means: move number from R3 into accumulator

ADD A, R4; Means: add number from R4 to accumulator (result remains in

accumulator)

MOV R5, A; Means: temporarily moves the result from accumulator into R5

MOV A, R1; Means: move number from R1 into accumulator

ADD A, R2; Means: add number from R2 to accumulator

SUBB A, R5; Means: subtract number from R5 (there are R3+R4)

8051 Register Banks and Stack

RAM memory space allocation in the 8051

There are 128 bytes of RAM in the 8051. The 128 bytes of RAM inside

the 8051 are assigned addresses 00 to7FH. These 128 bytes are divided into three

different groups as follows:

1. A total of 32 bytes from locations 00 to 1FH hex are set aside for

register banks and the stack.

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2. A total of 16 bytes from locations 20 to 2FH hex are set aside for bit-

addressable read/write memory.

3. A total of 80 bytes from locations 30H to 7FH are used for read and

write storage, or what is normally called Scratch pad. These 80

locations of RAM are widely used for the purpose of storing data and

parameters nu 8051 programmers.

Register banks in the 8051

A total of 32bytes of RAM are set aside for the register banks and stack.

These 32 bytes are divided into 4 banks of registers in which each bank has

registers, R0-R7. RAM locations 0 to 7 are set aside for bank 0 of R0-R7 where

R0 is RAM location 0, R1 is RAM location 1, and R2 is location 2, and so on,

until memory location7, which belongs to R7 of bank0. The second bank of

registers R0-R7 starts at RAM location 08 and goes to location 0FH. The third

bank of R0-R7 starts at memory location 10H and goes to location 17H. Finally,

RAM locations 18H to 1FH are set aside for the fourth bank of R0-R7. Fig shows

how the 32 bytes are allocated into 4 banks.

As we can see from fig 1, the bank 1 uses the same RAM space as the

stack. This is a major problem in programming the 8051. we must either not use

register bank1, or allocate another area of RAM for the stack.

Default register bank

If RAM locations 00-1F are set aside for the four register banks, which

register bank of R0-R7 do we have access to when the 8051 is powered up? The

answer is register bank 0; that is , RAM locations 0, 1,2,3,4,5,6, and 7 are

accessed with the names R0, R1, R2, R3, R4, R5, R6, and R7 when programming

the 8051. It is much easier to refer to these RAM locations with names such as

R0, R1 and so on, than by their memory locations as shown in fig 2.

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The register banks are switched by using the D3 & D4 bits of register

PSW.

FIG: RAM Allocation in the 8051

Fig: 8051 Register Banks and their RAM Addresses

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PSW Register (Program Status Word)

This is one of the most important SFRs. The Program Status Word (PSW)

contains several status bits that reflect the current state of the CPU. This register

contains: Carry bit, Auxiliary Carry, two register bank select bits, Overflow flag,

parity bit, and user-definable status flag. The ALU automatically changes some of

register’s bits, which is usually used in regulation of the program performing.

P - Parity bit. If a number in accumulator is even then this bit will be

automatically set (1), otherwise it will be cleared (0). It is mainly used during data

transmission and receiving via serial communication.

- Bit 1. This bit is intended for the future versions of the microcontrollers, so it is

not supposed to be here.

OV Overflow occurs when the result of arithmetical operation is greater than 255

(decimal), so that it can not be stored in one register. In that case, this bit will be

set (1). If there is no overflow, this bit will be cleared (0).

RS0, RS1 - Register bank selects bits. These two bits are used to select one of the

four register banks in RAM. By writing zeroes and ones to these bits, a group of registers

R0-R7 is stored in one of four banks in RAM.

RS1 RS2 Space in RAM

0 0 Bank0 00h-07h

0 1 Bank1 08h-0Fh

1 0 Bank2 10h-17h

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1 1 Bank3 18h-1Fh

F0 - Flag 0. This is a general-purpose bit available to the user.

AC - Auxiliary Carry Flag is used for BCD operations only.

CY - Carry Flag is the (ninth) auxiliary bit used for all arithmetical operations

and shift instructions.

DPTR Register (Data Pointer)

These registers are not true ones because they do not physically exist. They

consist of two separate registers: DPH (Data Pointer High) and (Data Pointer

Low). Their 16 bits are used for external memory addressing. They may be

handled as a 16-bit register or as two independent 8-bit registers. Besides, the

DPTR Register is usually used for storing data and intermediate results which

have nothing to do with memory locations.

SP Register (Stack Pointer)

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The stack is a section of RAM used by the CPU to store information

temporarily. This information could be data or an address. The CPU needs this

storage area since there are only a limited number of registers.

How stacks are accessed in the 8051

If the stack is a section of RAM, there must be registers inside the CPU

to point to it. The register used to access the stack is called the SP (Stack point)

Register. The stack pointer in the 8051 is only 8 bits wide; which means that it

can take values of 00 to FFH. When the 8051 is powered up, the SP register

contains value 07. This means that RAM location 08 is the first location used for

the stack by the 8051. The storing of a CPU register in the stack is called a

PUSH, and pulling the contents off the stack back into a CPU register is called a

POP. In other words, a register is pushed onto the stack to save it and popped off

the stack to retrieve it. The job of the SP is very critical when push and pop

actions are performed.

Pushing onto the stack

In the 8051 the stack pointer (SP) points to the last used location of the

stack. As we push data onto the stack, the stack pointer is incremented by one.

Notice that this different from many microprocessors, notably x86 processors in

which the SP is decremented when data is pushed onto the stack. As each PUSH

is executed, the contents of the register are saved on the stack and SP is

incremented by 1. Notice that for every byte of data saved on the stack and then

SP is incremented only once. Notice also that to push the registers onto the stack

we must use their RAM addresses. For example, the instruction “PUSH” pushes

register R1 onto the stack.

28

Popping from the stack

Popping the contents of the stack back into a given register is the opposite

process of pushing. With every pop, the top byte of the stack is copied to the

register specified by the instruction and the stack pointer is decremented once.

The upper limit of the stack

As, mentioned earlier, locations 08 to 1FH in the 8051 RAM can be used

for the stack. This is because locations 20-2FH of RAM are reserved for bit-

addressable memory and must not be used by the stack. If in a program we need

more than 24 bytes (08 to 1FH=24bytes) of stack, we can change the SP to point

to RAM locations 30-7FH. This is done with the instruction “MOV SP, #XX”.

P0, P1, P2, P3 - Input/Output Registers

In case that external memory and serial communication system are not in use then,

4 ports with in total of 32 input-output lines are available to the user for

connection to peripheral environment. Each bit inside these ports corresponds to

the appropriate pin on the microcontroller. This means that logic state written to

these ports appears as a voltage on the pin (0 or 5 V). Naturally, while reading, the

opposite occurs – voltage on some input pins is reflected in the appropriate port

bit.

The state of a port bit, besides being reflected in the pin, determines at the same

time whether it will be configured as input or output. If a bit is cleared (0), the pin

will be configured as output. In the same manner, if a bit is set to 1 the pin will be

configured as input. After reset, as well as when turning the microcontroller ON,

29

all bits on these ports are set to one (1). This means that the appropriate pins will

be configured as inputs.

Program counter:

The important register in the 8051 is the PC (Program counter). The

program counter points to the address of the next instruction to be executed. As

the CPU fetches the OPCODE from the program ROM, the program counter is

incremented to point to the next instruction. The program counter in the 8051 is

16bits wide. This means that the 8051 can access program addresses 0000 to

FFFFH, a total of 64k bytes of code. However, not all members of the 8051 have

the entire 64K bytes of on-chip ROM installed, as we will see soon.

Types of instructions

Depending on operation they perform, all instructions are divided in several

groups:

Arithmetic Instructions

Branch Instructions

Data Transfer Instructions

Logical Instructions

Logical Instructions with bits

The first part of each instruction, called MNEMONIC refers to the operation an

instruction performs (copying, addition, logical operation etc.). Mnemonics

commonly are shortened form of name of operation being executed. For example:

INC R1; Increment R1 (increment register R1)

LJMP LAB5 ;Long Jump LAB5 (long jump to address specified as LAB5)

JNZ LOOP ;Jump if Not Zero LOOP (if the number in the accumulator is not 0,

jump to address specified as LOOP)

30

Another part of instruction, called OPERAND is separated from mnemonic at

least by one empty space and defines data being processed by instructions. Some

instructions have no operand; some have one, two or three. If there is more than

one operand in instruction, they are separated by comma. For example:

RET - (return from sub-routine)

JZ TEMP - (if the number in the accumulator is not 0, jump to address specified

as TEMP)

ADD A,R3 - (add R3 and accumulator)

CJNE A,#20,LOOP - (compare accumulator with 20. If they are not equal, jump

to address specified as LOOP)

Arithmetic instructions

These instructions perform several basic operations (addition, subtraction,

division, multiplication etc.) After execution, the result is stored in the first

operand. For example:

ADD A, R1 - The result of addition (A+R1) will be stored in the accumulator.

Arithmetical Instructions

Mnemonic DescriptionByte

Number

Oscillator

Period

ADD A,Rn Add R Register to accumulator 1 1

ADD A,RxAdd directly addressed Rx Register to

accumulator2 2

ADD

A,@Ri

Add indirectly addressed Register to

accumulator1 1

ADD A,#X Add number X to accumulator 2 2

31

ADDC

A,Rn

Add R Register with Carry bit to

accumulator1 1

Branch Instructions

There are two kinds of these instructions:

Unconditional jump instructions: After their execution a jump to a new location

from where the program continues execution is executed.

Conditional jump instructions: If some condition is met - a jump is executed.

Otherwise, the program normally proceeds with the next instruction.

Branch Instruction

Mnemonic DescriptionByte

Number

Oscillator

Period

ACALL

adr11

Call subroutine located at address within 2

K byte Program Memory space2 3

LCALL

adr16

Call subroutine located at any address

within 64 K byte Program Memory space3 4

RET Return from subroutine 1 4

RETI Return from interrupt routine 1 4

AJMP adr11Jump to address located within 2 K byte

Program Memory space2 3

LJMP adr16Jump to any address located within 64 K

byte Program Memory space3 4

Data Transfer Instructions

32

These instructions move the content of one register to another one. The register which

content is moved remains unchanged. If they have the suffix “X” (MOVX), the data is

exchanged with external memory.

Data Transfer Instruction

Mnemonic DescriptionByte

Number

Cycle

Number

MOV A,Rn Move R register to accumulator 1 1

MOV A,RxMove directly addressed Rx register to

accumulator2 2

MOV

A,@Ri

Move indirectly addressed register to

accumulator1 1

MOV A,#X Move number X to accumulator 2 2

Logical Instructions

These instructions perform logical operations between corresponding bits of two

registers. After execution, the result is stored in the first operand.

Logical Instructions

Mnemonic DescriptionByte

Number

Cycle

Number

ANL A,RnLogical AND between accumulator and R

register1 1

ANL A,Rx Logical AND between accumulator and 2 2

33

directly addressed register Rx

ANL A,@RiLogical AND between accumulator and

indirectly addressed register1 1

ANL A,#XLogical AND between accumulator and

number X2 2

Logical Operations on Bits

Similar to logical instructions, these instructions perform logical operations. The

difference is that these operations are performed on single bits.

Logical operations on bits

Mnemonic DescriptionByte

Number

Cycle

Number

CLR C Clear Carry bit 1 1

CLR bit Clear directly addressed bit 2 2

SETB C Set Carry bit 1 1

SETB bit Set directly addressed bit 2 2

CPL C Complement Carry bit 1 1

CPL bit Complement directly addressed bit 2 2

34

TIMERSOn-chip timing/counting facility has proved the capabilities of the

microcontroller for implementing the real time application. These includes pulse

counting, frequency measurement, pulse width measurement, baud rate

generation, etc,. Having sufficient number of timer/counters may be a need in a

certain design application. The 8051 has two timers/counters. They can be used

either as timers to generate a time delay or as counters to count events happening

outside the microcontroller. Let discuss how these timers are used to generate

time delays and we will also discuss how they are been used as event counters.

PROGRAMMING 8051 TIMERS

The 8051 has timers: Timer 0 and Timer1.they can be used either as timers

or as event counters. Let us first discuss about the timers’ registers and how to

program the timers to generate time delays.

BASIC RIGISTERS OF THE TIMER

Both Timer 0 and Timer 1 are 16 bits wide. Since the 8051 has an 8-bit

architecture, each 16-bit timer is accessed as two separate registers of low byte

and high byte.

TIMER 0 REGISTERS

The 16-bit register of Timer 0 is accessed as low byte and high byte. the

low byte register is called TL0(Timer 0 low byte)and the high byte register is

referred to as TH0(Timer 0 high byte).These register can be accessed like any

other register, such as A,B,R0,R1,R2,etc.for example, the instruction ”MOV

TL0, #4F”moves the value 4FH into TL0,the low byte of Timer 0.These registers

can also be read like any other register.

35

TIMER 1 REGISTERS

Timer 1 is also 16-bit register is split into two bytes, referred to as TL1

(Timer 1 low byte) and TH1 (Timer 1 high byte).these registers are accessible n

the same way as the register of Timer 0.

TMOD (timer mode) REGISTER

Both timers TIMER 0 and TIMER 1 use the same register, called TMOD,

to set the various timer operation modes. TMOD is an 8-bit register in which the

lower 4 bits are set aside for Timer 0 and the upper 4 bits for Timer 1.in each

case; the lower 2 bits are used to set the timer mode and the upper 2 bits to specify

the operation.

MODES:

M1, M0:

M0 and M1 are used to select the timer mode. There are three modes: 0,

1, 2.Mode 0 is a 13-bit timer, mode 1 is a 16-bit timer, and mode 2 is an 8-bit

timer. We will concentrate on modes 1 and 2 since they are the ones used most

widely. We will soon describe the characteristics of these modes, after describing

the reset of the TMOD register.

36

GATE Gate control when set. The timer/counter is

enabled only

While the INTx pin is high and the TRx control

pin is.

Set. When cleared, the timer is enabled.

C/T Timer or counter selected cleared for timer

operation

(Input from internal system clock).set for

counter

Operation (input TX input pin).

M 1 Mode bit 1

M0 Mode bit 0

M1 M0 MODE Operating Mode

0 0 0 13-bit timer mode

8-bit timer/counter THx with TLx

as

5 - Bit pre-scaler.

0 1 1 16-bit timer mode

16-bit timer/counters THx with

TLx are

Cascaded; there is no prescaler

37

1 0 2 8-bit auto reload

8-bit auto reload

timer/counter;THx

Holds a value that is to be reloaded

into

TLx each time it overflows.

1 1 3 Split timer mode.

C/T (clock/timer)

This bit in the TMOD register is used to decide whether the timer is used as a

delay generator or an event counter. If C/T=0, it is used as a timer for time delay

generation. The clock source for the time delay is the crystal frequency of the

8051. This section is concerned with this choice. The timer’s use as an event

counter is discussed in the next section.

Serial Communication:

Computers can transfer data in two ways: parallel and serial. In parallel

data transfers, often 8 or more lines (wire conductors) are used to transfer data to a

device that is only a few feet away. Examples of parallel data transfer are printers

and hard disks; each uses cables with many wire strips. Although in such cases a

lot of data can be transferred in a short amount of time by using many wires in

parallel, the distance cannot be great. To transfer to a device located many meters

away, the serial method is used. In serial communication, the data is sent one bit

at a time, in contrast to parallel communication, in which the data is sent a byte or

more at a time. Serial communication of the 8051 is the topic of this chapter. The

38

8051 has serial communication capability built into it, there by making possible

fast data transfer using only a few wires.

If data is to be transferred on the telephone line, it must be converted

from 0s and 1s to audio tones, which are sinusoidal-shaped signals. A peripheral

device called a modem, which stands for “modulator/demodulator”, performs this

conversion.

Serial data communication uses two methods, asynchronous and

synchronous. The synchronous method transfers a block of data at a time, while

the asynchronous method transfers a single byte at a time.

In data transmission if the data can be transmitted and received, it is a

duplex transmission. This is in contrast to simplex transmissions such as with

printers, in which the computer only sends data. Duplex transmissions can be half

or full duplex, depending on whether or not the data transfer can be simultaneous.

If data is transmitted one way at a time, it is referred to as half duplex. If the data

can go both ways at the same time, it is full duplex. Of course, full duplex

requires two wire conductors for the data lines, one for transmission and one for

reception, in order to transfer and receive data simultaneously.

Asynchronous serial communication and data framing

The data coming in at the receiving end of the data line in a serial data

transfer is all 0s and 1s; it is difficult to make sense of the data unless the sender

and receiver agree on a set of rules, a protocol, on how the data is packed, how

many bits constitute a character, and when the data begins and ends.

Start and stop bits

Asynchronous serial data communication is widely used for character-

oriented transmissions, while block-oriented data transfers use the synchronous

method. In the asynchronous method, each character is placed between start and

stop bits. This is called framing. In the data framing for asynchronous

communications, the data, such as ASCII characters, are packed between a start

39

bit and a stop bit. The start bit is always one bit, but the stop bit can be one or two

bits. The start bit is always a 0 (low) and the stop bit (s) is 1 (high).

Data transfer rate

The rate of data transfer in serial data communication is stated in bps

(bits per second). Another widely used terminology for bps is baud rate.

However, the baud and bps rates are not necessarily equal. This is due to the fact

that baud rate is the modem terminology and is defined as the number of signal

changes per second. In modems a single change of signal, sometimes transfers

several bits of data. As far as the conductor wire is concerned, the baud rate and

bps are the same, and for this reason we use the bps and baud interchangeably.

The data transfer rate of given computer system depends on

communication ports incorporated into that system. For example, the early

IBMPC/XT could transfer data at the rate of 100 to 9600 bps. In recent years,

however, Pentium based PCS transfer data at rates as high as 56K bps. It must be

noted that in asynchronous serial data communication, the baud rate is generally

limited to 100,000bps.

RS232 Standards

To allow compatibility among data communication equipment made by

various manufacturers, an interfacing standard called RS232 was set by the

Electronics Industries Association (EIA) in 1960. In 1963 it was modified and

called RS232A. RS232B AND RS232C were issued in 1965 and 1969,

respectively. Today, RS232 is the most widely used serial I/O interfacing

standard. This standard is used in PCs and numerous types of equipment.

However, since the standard was set long before the advert of the TTL logic

family, its input and output voltage levels are not TTL compatible. In RS232, a 1

is represented by -3 to -25V, while a 0 bit is +3 to +25V, making -3 to +3

undefined. For this reason, to connect any RS232 to a microcontroller system we

must use voltage converters such as MAX232 to convert the TTL logic levels to

40

the RS232 voltage levels, and vice versa. MAX232 IC chips are commonly

referred to as line drivers.

RS232 pins

RS232 cable is commonly referred to as the DB-25 connector. In labeling,

DB-25P refers to the plug connector (male) and DB-25S is for the socket

connector (female). Since not all the pins are used in PC cables, IBM introduced

the DB-9 Version of the serial I/O standard, which uses 9 pins only, as shown in

table.

DB-9 pin connector

1 2 3 4 5

6 7 8 9

(Out of computer and exposed end of cable)

Pin Functions:

Pin Description

1 Data carrier detect (DCD)

2 Received data (RXD)

3 Transmitted data (TXD)

4 Data terminal ready(DTR)

5 Signal ground (GND)

6 Data set ready (DSR)

7 Request to send (RTS)

8 Clear to send (CTS)

9 Ring indicator (RI)

Note: DCD, DSR, RTS and CTS are active low pins.

41

The method used by RS-232 for communication allows for a simple connection

of three lines: Tx, Rx, and Ground. The three essential signals for 2-way RS-232

Communications are these:

TXD: carries data from DTE to the DCE.

RXD: carries data from DCE to the DTE

SG: signal ground

8051 connection to RS232

The RS232 standard is not TTL compatible; therefore, it requires a line

driver such as the MAX232 chip to convert RS232 voltage levels to TTL levels,

and vice versa. The interfacing of 8051 with RS232 connectors via the MAX232

chip is the main topic.

The 8051 has two pins that are used specifically for transferring

and receiving data serially. These two pins are called TXD and RXD and a part of

the port 3 group (P3.0 and P3.1). Pin 11 of the 8051 is assigned to TXD and pin

10 is designated as RXD. These pins are TTL compatible; therefore, they require

a line driver to make them RS232 compatible. One such line driver is the

MAX232 chip.

MAX232 converts from RS232 voltage levels to TTL

voltage levels, and vice versa. One advantage of the MAX232 chip is that it uses

a +5V power source which, is the same as the source voltage for the 8051. In the

other words, with a single +5V power supply we can power both the 8051 and

MAX232, with no need for the power supplies that are common in many older

systems. The MAX232 has two sets of line drivers for transferring and receiving

42

data. The line drivers used for TXD are called T1 and T2, while the line drivers

for RXD are designated as R1 and R2. In many applications only one of each is

used.

CONNECTING μC to PC using MAX 232

INTERRUPTSA single microcontroller can serve several devices. There are two ways to do that:

INTERRUPTS or POLLING.

POLLING:

In polling the microcontroller continuously monitors the status of a given device;

when the status condition is met, it performs the service .After that, it moves on to

monitor the next device until each one is serviced. Although polling can monitor

the status of several devices and serve each of them as certain condition are met.

43

INTERRUPTS:

In the interrupts method, whenever any device needs its

service, the device notifies the microcontroller by sending it an interrupts signal.

Upon receiving an interrupt signal, the microcontroller interrupts whatever it is

doing and serves the device. The program associated with the interrupts is called

the interrupt service routine (ISR).or interrupt handler.

INTERRUPTS Vs POLLING:

The advantage of interrupts is that the microcontroller can serve many

devices (not all the same time, of course); each device can get the attention of

the microcontroller based on the priority assigned to it. The polling method

cannot assign priority since it checks all devices in round-robin fashion. More

importantly, in the interrupt method the microcontroller can also ignore (mask)

a device request for service. This is again not possible with the polling

method. The most important reason that the interrupt method is preferable is

that the polling method wastes much of the microcontroller’s time by polling

devices that do not need service. So, in order to avoid tying down the

microcontroller, interrupts are used.

INTERRUPT SERVICE ROUTINE

44

For every interrupt, there must be an interrupt service routine (ISR), or interrupt

handler. When an interrupt is invoked, the microcontroller runs the interrupts

service routine. For every interrupt, there is a fixed location in memory that holds

the address of its ISR. The group of memory location set aside to hold the

addresses of ISR and is called the Interrupt Vector Table. Shown below:

Interrupt Vector Table for the 8051:

S.No. INTERRUPT ROM LOCATION

(HEX)

PIN FLAG

CLEARING

1. Reset 0000 9 Auto

2. External

hardware

Interrupt 0

0003 P3.2 (12) Auto

3. Timers 0 interrupt (TF0)

000B Auto

4. External

hardware

Interrupt

1(INT1)

0013 P3.3 (13) Auto

5. Timers 1 interrupt (TF1)

001B Auto

45

6. Serial COM (RI and TI)

0023 Programmer clears it

Six Interrupts in the 8051:

In reality, only five interrupts are available to the user in the 8051, but many

manufacturers’ data sheets state that there are six interrupts since they include

reset .the six interrupts in the 8051 are allocated as above.

1. Reset. When the reset pin is activated, the 8051 jumps to address location

0000.this is the power-up reset.

2. Two interrupts are set aside for the timers: one for Timer 0 and one for

Timer 1.Memory location 000BH and 001BH in the interrupt vector table

belong to Timer 0 and Timer 1, respectively.

3. Two interrupts are set aside for hardware external harder interrupts. Pin

number 12(P3.2) and 13(P3.3) in port 3 are for the external hardware

interrupts INT0 and INT1,respectively.These external interrupts are also

referred to as EX1 and EX2.Memory location 0003H and 0013H in the

interrupt vector table are assigned to INT0 and INT1, respectively.

4. Serial communication has a single interrupt that belongs to both receive

and transmit. The interrupt vector table location 0023H belongs to this

interrupt.

Notice that a limited number of bytes are set aside for each interrupt. For example,

a total of 8 bytes from location 0003 to 000A is set aside for INT0, external

hardware interrupt 0.similarly,a total of 8 bytes from location 00BH to 0012H is

reserved for TF0, Timer 0 interrupt. If the service routine for a given interrupt is

short enough to fit in the memory space allocated to it, it is placed in the vector

table; otherwise, and an LJMP instruction is placed in the vector table to point to

the address of the ISR. In that rest of the bytes allocated to that interrupt are

unused.

46

From the above table also notice that only three bytes of ROM space are assigned

to the reset pin. they are ROM address location 0,1 and2.address location 3

belongs to external hardware interrupt 0.for this reason, in our program we put

the LJMP as the first instruction and redirect the processor away from the

interrupt vector table, as shown below

Steps in executing an interrupt

Upon activation of an interrupt, the microcontroller goes through the following

steps.

1. It finishes the instruction it is executing and saves the address of the next

instruction (PC) on the stack.

2. It also saves the current status of all the interrupts internally (i.e., not on the

stack).

3. It jumps to a fixed location in memory called the interrupt vector table that

holds the address of the interrupts service routine.

4. The microcontroller gets the address of the ISR from the interrupt vector

table and jumps to it. It starts to execute the interrupt service subroutine

until it reaches the last instruction of the subroutine, which is RETI (return

from interrupt).

5. Upon executing the RETI instruction, the microcontroller returns to the

place where it was interrupted. First, it gets the program counter (PC)

address from the stack by popping the top two bytes of the stack into the

PC. Then it starts to execute from that address.

Notice from step 5 the critical role of the stack. For this reason, we must be

careful in manipulating the stack contents in the ISR. Specifically, in the ISR, just

as in any CALL subroutine, the number of pushes and pops must be equal.

Enabling and disabling an interrupt:

Upon reset, all interrupt are disabled (masked), meaning that none will be

responded to by the microcontroller if they are activated. The interrupt must be

enabled by software in order for the microcontroller to respond to them. There is a

47

register called IE (interrupt enable) that is responsible for enabling (unmasking)

and disabling (masking) the interrupts.

Notice that IE is a bit-addressable register.

Steps in enabling an interrupt:

To enable an interrupt, we take the following steps:

1. Bit D7 of the IE register (EA) must be set to high to allow the reset to take

effect.

If EA=1, interrupts are enabled and will be responded to if their corresponding bit

in IE are high. If EA=0, no interrupt will be responded to, even if the associated

bit in the IE register is high.

Interrupt Enable Register

D7 D6 D5 D4 D3 D2 D1 D0

EA IE.7 disables all interrupts. If EA=0, no interrupts is

acknowledged.

If EA=1, each interrupt source is individually enabled

disabled

By setting or clearing its enable bit.

-- IE.6 Not implemented, reserved for future use.*

ET2 IE.5 Enables or disables Timer 2 overflow or capture interrupt

(8052

Only)

48

EA -- ET2 ES ET1 EX1 ET0 EX0

ES IE.4 Enables or disables the serial port interrupts.

ET1 IE.3 Enables or disables Timers 1 overflow interrupt

EX1 IE.2 Enables or disables external interrupt 1.

ET0 IE.1 Enables or disables Timer 0 overflow interrupt.

EX0 IE.0 Enables or disables external interrupt.

Power supply

The power supplies are designed to convert high voltage

AC mains electricity to a suitable low voltage supply for electronics circuits and

other devices. A power supply can by broken down into a series of blocks, each of

which performs a particular function. A d.c power supply which maintains the

output voltage constant irrespective of a.c mains fluctuations or load variations is

known as “Regulated D.C Power Supply”

For example a 5V regulated power supply system as shown below:

49

Transformer:

A transformer is an electrical device which is used to convert electrical power from one Electrical circuit to another without change in frequency.

Transformers convert AC electricity from one voltage to another with little

loss of power. Transformers work only with AC and this is one of the reasons why

mains electricity is AC. Step-up transformers increase in output voltage, step-

down transformers decrease in output voltage. Most power supplies use a step-

down transformer to reduce the dangerously high mains voltage to a safer low

voltage. The input coil is called the primary and the output coil is called the

secondary. There is no electrical connection between the two coils; instead they

are linked by an alternating magnetic field created in the soft-iron core of the

transformer. The two lines in the middle of the circuit symbol represent the core.

Transformers waste very little power so the power out is (almost) equal to the

power in. Note that as voltage is stepped down current is stepped up. The ratio of

50

the number of turns on each coil, called the turn’s ratio, determines the ratio of the

voltages. A step-down transformer has a large number of turns on its primary

(input) coil which is connected to the high voltage mains supply, and a small

number of turns on its secondary (output) coil to give a low output voltage.

An Electrical Transformer

Turns ratio = Vp/ VS = Np/NS

Power Out= Power In

VS X IS=VP X IP

Vp = primary (input) voltage

Np = number of turns on primary coil

Ip  = primary (input) current    

RECTIFIER:

A circuit which is used to convert a.c to dc is known as RECTIFIER. The process of conversion a.c to d.c is called “rectification”

51

TYPES OF RECTIFIERS:

Half wave Rectifier Full wave rectifier

1. Centre tap full wave rectifier.

2. Bridge type full bridge rectifier.

Comparison of rectifier circuits:

Parameter

Type of Rectifier

Half wave Full wave Bridge

Number of diodes

1

2

4

PIV of diodes

Vm

2Vm

Vm

D.C output voltage

Vm/

2Vm/

2Vm/

Vdc,at

no-load

0.318Vm

0.636Vm 0.636Vm

Ripple factor

1.21

0.482

0.482

Ripple

frequency

f

2f

2f

Rectification

efficiency

0.406

0.812

0.812

52

Transformer

Utilization

Factor(TUF)

0.287 0.693 0.812

RMS voltage Vrms Vm/2 Vm/√2 Vm/√2

Full-wave Rectifier:

From the above comparision we came to know that full wave bridge rectifier as more advantages than the other two rectifiers. So, in our project we are using full wave bridge rectifier circuit.

Bridge Rectifier: A bridge rectifier makes use of four diodes in a bridge

arrangement to achieve full-wave rectification. This is a widely used

configuration, both with individual diodes wired as shown and with single

component bridges where the diode bridge is wired internally.

A bridge rectifier makes use of four diodes in a bridge arrangement as

shown in fig(a) to achieve full-wave rectification. This is a widely used

configuration, both with individual diodes wired as shown and with single

component bridges where the diode bridge is wired internally.

Fig(A)

53

Operation:

During positive half cycle of secondary, the diodes D2 and D3 are in forward

biased while D1 and D4 are in reverse biased as shown in the fig(b). The current

flow direction is shown in the fig (b) with dotted arrows.

Fig(B)

During negative half cycle of secondary voltage, the diodes D1 and D4 are in

forward biased while D2 and D3 are in reverse biased as shown in the fig(c). The

current flow direction is shown in the fig (c) with dotted arrows.

Fig(C)

Filter:

54

A Filter is a device which removes the a.c component of rectifier output

but allows the d.c component to reach the load

Capacitor Filter:

We have seen that the ripple content in the rectified output of half wave

rectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48%

such high percentages of ripples is not acceptable for most of the applications.

Ripples can be removed by one of the following methods of filtering.

(a) A capacitor, in parallel to the load, provides an easier by –pass for the ripples

voltage though it due to low impedance. At ripple frequency and leave the d.c.to

appears the load.

(b) An inductor, in series with the load, prevents the passage of the ripple current

(due to high impedance at ripple frequency) while allowing the d.c (due to low

resistance to d.c)

(c) various combinations of capacitor and inductor, such as L-section filter

section filter, multiple section filter etc. which make use of both the properties

mentioned in (a) and (b) above. Two cases of capacitor filter, one applied on half

wave rectifier and another with full wave rectifier.

55

Filtering is performed by a large value electrolytic capacitor connected

across the DC supply to act as a reservoir, supplying current to the output when

the varying DC voltage from the rectifier is falling. The capacitor charges quickly

near the peak of the varying DC, and then discharges as it supplies current to the

output. Filtering significantly increases the average DC voltage to almost the peak

value (1.4 × RMS value).

To calculate the value of capacitor(C),

C = ¼*√3*f*r*Rl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000µF Hence large value of capacitor is

placed to reduce ripples and to improve the DC component.

Regulator:

Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable

output voltages. The maximum current they can pass also rates them. Negative

voltage regulators are available, mainly for use in dual supplies. Most regulators

include some automatic protection from excessive current ('overload protection')

and overheating ('thermal protection'). Many of the fixed voltage regulator ICs

have 3 leads and look like power transistors, such as the 7805 +5V 1A regulator

shown on the right. The LM7805 is simple to use. You simply connect the

positive lead of your unregulated DC power supply (anything from 9VDC to

24VDC) to the Input pin, connect the negative lead to the Common pin and then

when you turn on the power, you get a 5 volt supply from the output pin.

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Fig 6.1.6 A Three Terminal Voltage Regulator

78XX:

The Bay Linear LM78XX is integrated linear positive regulator with three

terminals. The LM78XX offer several fixed output voltages making them useful

in wide range of applications. When used as a zener diode/resistor combination

replacement, the LM78XX usually results in an effective output impedance

improvement of two orders of magnitude, lower quiescent current. The LM78XX

is available in the TO-252, TO-220 & TO-263packages

Features:

• Output Current of 1.5A

• Output Voltage Tolerance of 5%

• Internal thermal overload protection

• Internal Short-Circuit Limited

• No External Component

• Output Voltage 5.0V, 6V, 8V, 9V, 10V,12V, 15V, 18V, 24V

• Offer in plastic TO-252, TO-220 & TO-263

• Direct Replacement for LM78XX

LINEAR KEYPAD

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This section basically consists of a Linear Keypad. Basically a Keypad can be

classified into 2 categories. One is Linear Keypad and the other is Matrix keypad.

1. Matrix Keypad.

2. Linear Keypad.

1. Matrix Keypad: This Keypad got keys arranged in the form of Rows and

Columns. That is why the name Matrix Keypad. According to this keypad,

In order to find the key being pressed the keypad need to be scanned by

making rows as i/p and columns as output or vice versa.

This Keypad is used in places where one needs to connect

more no. of keys with less no. of data lines.

2. Linear Keypad: This Keypad got ‘n’ no. of keys connected to ‘n’ data

lines of microcontroller.

This Keypad is used in places where one needs to connect

less no. of keys.

Generally, in Linear Keypads one end of the switch is connected to

Microcontroller (Configured as i/p) and other end of the switch is connected to

the common ground. So whenever a key of Linear Keypad is pressed the logic

on the microcontroller pin will go LOW.

Here in this project, a linear keypad is used with switches connected in a

serial manner. Linear keypad is used in this project because it takes less no. of

port pins. The Linear Keypad with 4 Keys is shown below.

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MAX-232:

The MAX232 from Maxim was the first IC which in one package contains the necessary drivers (two) and receivers (also two), to adapt the RS-232 signal voltage levels to TTL logic. It became popular, because it just needs one voltage (+5V) and generates the necessary RS-232 voltage levels (approx. -10V and +10V) internally. This greatly simplified the design of circuitry. Circuitry designers no longer need to design and build a power supply with three voltages (e.g. -12V, +5V, and +12V), but could just provide one +5V power supply, e.g. with the help of a simple 78x05 voltage converter.

The MAX232 has a successor, the MAX232A. The ICs are almost identical, however, the MAX232A is much more often used (and easier to get) than the original MAX232, and the MAX232A only needs external capacitors 1/10th the capacity of what the original MAX232 needs.

It should be noted that the MAX 232(A) is just a driver/receiver. It does not generate the necessary RS-232 sequence of marks and spaces with the right timing, it does not decode the RS-232 signal, it does not provide a serial/parallel conversion. All it does is to convert signal voltage levels. Generating serial data

59

with the right timing and decoding serial data has to be done by additional circuitry, e.g. by a 16550 UART or one of these small micro controllers (e.g. Atmel AVR, Microchip PIC) getting more and more popular.

The MAX232 and MAX232A were once rather expensive ICs, but today they are cheap. It has also helped that many companies now produce clones (ie. Sipex). These clones sometimes need different external circuitry, e.g. the capacities of the external capacitors vary. It is recommended to check the data sheet of the particular manufacturer of an IC instead of relying on Maxim's original data sheet.

The original manufacturer (and now some clone manufacturers, too) offers a large series of similar ICs, with different numbers of receivers and drivers, voltages, built-in or external capacitors, etc. E.g. The MAX232 and MAX232A need external capacitors for the internal voltage pump, while the MAX233 has these capacitors built-in. The MAX233 is also between three and ten times more expensive in electronic shops than the MAX232A because of its internal capacitors. It is also more difficult to get the MAX233 than the garden variety MAX232A.

A Typical Application

The MAX 232(A) has two receivers (converts from RS-232 to TTL voltage levels) and two drivers (converts from TTL logic to RS-232 voltage levels). This means only two of the RS-232 signals can be converted in each direction. The old MC1488/1498 combo provided four drivers and receivers.

Typically a pair of a driver/receiver of the MAX232 is used for

TX and RX

And the second one for

CTS and RTS.

There are not enough drivers/receivers in the MAX232 to also connect the DTR, DSR, and DCD signals. Usually these signals can be omitted when e.g. communicating with a PC's serial interface. If the DTE really requires these signals either a second MAX232 is needed, or some other IC from the MAX232 family can be used (if it can be found in consumer electronic shops at all). An alternative for DTR/DSR is also given below.

Maxim's data sheet explains the MAX232 family in great detail, including the pin configuration and how to connect such an IC to external circuitry. This information can be used as-is in own design to get a working RS-232 interface. Maxim's data just misses one critical piece of information: How exactly to connect the RS-232 signals to the IC. So here is one possible example:

60

MAX232 to RS232 DB9 Connection as a DCE

MAX232 Pin Nbr. MAX232 Pin Name Signal Voltage DB9 Pin

7 T2out CTS RS-232 7

8 R2in RTS RS-232 8

9 R2out RTS TTL n/a

10 T2in CTS TTL n/a

11 T1in TX TTL n/a

12 R1out RX TTL n/a

13 R1in TX RS-232 3

14 T1out RX RS-232 2

15 GND GND 0 5

In addition one can directly wire DTR (DB9 pin 4) to DSR (DB9 pin 6) without going through any circuitry. This gives automatic (brain dead) DSR acknowledgment of an incoming DTR signal.

Sometimes pin 6 of the MAX232 is hard wired to DCD (DB9 pin 1). This is not recommended. Pin 6 is the raw output of the voltage pump and inverter for the -10V voltage. Drawing currents from the pin leads to a rapid breakdown of the voltage, and as a consequence to a breakdown of the output voltage of the two RS-232 drivers. It is better to use software which doesn't care about DCD, but does hardware-handshaking via CTS/RTS only.

The circuitry is completed by connecting five capacitors to the IC as it follows. The MAX232 needs 1.0µF capacitors, the MAX232A needs 0.1µF capacitors. MAX232 clones show similar differences. It is recommended to consult the corresponding data sheet. At least 16V capacitor types should be used. If electrolytic or tantalic capacitors are used, the polarity has to be observed. The first pin as listed in the following table is always where the plus pole of the capacitor should be connected to.

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MAX232(A) external Capacitors

Capacitor + Pin - Pin Remark

C1 1 3

C2 4 5

C3 2 16

C4 GND 6This looks non-intuitive, but because pin 6 ison -10V, GND gets the + connector, and not the -

C5 16 GND

The 5V power supply is connected to

+5V: Pin 16 GND: Pin 15

Features

Meet or Exceed TIA/EIA-232-F and ITURecommendation V.28

Operate With Single 5-V Power Supply Operate Up to 120 kbit/s Two Drivers and Two Receivers 30-V Input Levels Low Supply Current . . . 8 mA Typical Designed to be Interchangeable WithMaxim MAX232

ESD Protection Exceeds JESD 22 2000-V Human-Body Model (A114-A)

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ApplicationsTIA/EIA-232-F

Battery-Powered Systems

Terminals

Modems

Computers

Description/ordering information

The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to supply EIA-232 voltage levels from a single 5-V supply. Each receiver converts EIA-232 inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of 1.3 V and a typical hysteresis of 0.5 V, and can accept 30-V inputs. Each driver converts TTL/CMOS input levels into EIA-232 levels. The driver, receiver, and voltage-generator functions are available as cells in the Texas Instruments Lin ASIClibrary.

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64

65

66

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Liquid crystal display

68

Liquid crystal displays (LCDs) have materials, which combine the

properties of both liquids and crystals. Rather than having a melting point, they

have a temperature range within which the molecules are almost as mobile as they

would be in a liquid, but are grouped together in an ordered form similar to a

crystal.

An LCD consists of two glass panels, with the liquid crystal material sand

witched in between them. The inner surface of the glass plates are coated with

transparent electrodes which define the character, symbols or patterns to be

displayed polymeric layers are present in between the electrodes and the liquid

crystal, which makes the liquid crystal molecules to maintain a defined orientation

angle.

One each polarisers are pasted outside the two glass panels. These

polarisers would rotate the light rays passing through them to a definite angle, in a

particular direction.

When the LCD is in the off state, light rays are rotated by the two

polarisers and the liquid crystal, such that the light rays come out of the LCD

without any orientation, and hence the LCD appears transparent.

When sufficient voltage is applied to the electrodes, the liquid crystal

molecules would be aligned in a specific direction. The light rays passing through

the LCD would be rotated by the polarisers, which would result in activating/

highlighting the desired characters.

The LCD’s are lightweight with only a few millimeters thickness. Since the

LCD’s consume less power, they are compatible with low power electronic

circuits, and can be powered for long durations.

The LCD’s don’t generate light and so light is needed to read the display.

By using backlighting, reading is possible in the dark. The LCD’s have long life

and a wide operating temperature range.

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Changing the display size or the layout size is relatively simple which

makes the LCD’s more customers friendly.

The LCDs used exclusively in watches, calculators and measuring

instruments are the simple seven-segment displays, having a limited amount of

numeric data. The recent advances in technology have resulted in better legibility,

more information displaying capability and a wider temperature range. These

have resulted in the LCDs being extensively used in telecommunications and

entertainment electronics. The LCDs have even started replacing the cathode ray

tubes (CRTs) used for the display of text and graphics, and also in small TV

applications.

This section describes the operation modes of LCD’s then describe how to

program and interface an LCD to 8051 using Assembly and C.

LCD operationIn recent years the LCD is finding widespread use replacing LEDs(seven-

segment LEDs or other multisegment LEDs).This is due to the following reasons:

1. The declining prices of LCDs.

2. The ability to display numbers, characters and graphics. This is in

contract to LEDs, which are limited to numbers and a few

characters.

3. Incorporation of a refreshing controller into the LCD, there by

relieving the CPU of the task of refreshing the LCD. In the

contrast,

the LED must be refreshed by the CPU to keep displaying the

data.

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4. Ease of programming for characters and graphics.

LCD pin description The LCD discussed in this section has 14 pins. The function of each pins is

given in table.

TABLE 1:Pin description for LCD:

Pin symbol I/O Description

1 Vss -- Ground

2 Vcc -- +5V power supply

3 VEE -- Power supply to

control contrast

4 RS I RS=0 to select

command register

RS=1 to select

data register

5 R/W I R/W=0 for write

R/W=1 for read

6 E I/O Enable

7 DB0 I/O The 8-bit data bus

8 DB1 I/O The 8-bit data bus

9 DB2 I/O The 8-bit data bus

10 DB3 I/O The 8-bit data bus

11 DB4 I/O The 8-bit data bus

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12 DB5 I/O The 8-bit data bus

13 DB6 I/O The 8-bit data bus

14 DB7 I/O The 8-bit data bus

TABLE 2: LCD Command Codes Code

(hex)

Command to LCD Instruction

Register

1 Clear display screen

2 Return home

4 Decrement cursor

6 Increment cursor

5 Shift display right

7 Shift display left

8 Display off, cursor off

A Display off, cursor on

C Display on, cursor off

E Display on, cursor on

F Display on, cursor blinking

10 Shift cursor position to left

14 Shift cursor position to right

18 Shift the entire display to the left

1C Shift the entire display to the right

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80 Force cursor to beginning of 1st line

C0 Force cursor to beginning of 2nd line

38 2 lines and 5x7 matrix

Uses:

The LCDs used exclusively in watches, calculators and measuring

instruments are the simple seven-segment displays, having a limited amount of

numeric data. The recent advances in technology have resulted in better legibility,

more information displaying capability and a wider temperature range. These

have resulted in the LCDs being extensively used in telecommunications and

entertainment electronics. The LCDs have even started replacing the cathode ray

tubes (CRTs) used for the display of text and graphics, and also in small TV

applications.

LCD INTERFACING

Sending commands and data to LCDs with a time delay:

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Fig 21: Interfacing of LCD to a micro controller

To send any command from table 2 to the LCD, make pin RS=0.

for data, make RS=1.Then send a high –to-low pulse to the E pin to enable the internal latch of the LCD.

SMARTCARD

Introduction

A smart card, chip card, or integrated circuit card (ICC), is any pocket-

sized card with embedded integrated circuits which can process data or Memory.

This implies that it can receive input which is processed — by way of the ICC

applications — and delivered as an output.A smart card resembles a credit card in

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size and shape, but inside it is completely different. First of all, it has an inside – a

normal credit card is a simple piece of plastic. The inside of a smart card usually

contains an Embedded Microprocessor or EEPROM (memory) or some times

both. The microprocessor is under a gold contact pad on one side of the card.

Think of the microprocessor as replacing the usual magnetic stripe on a credit

card or debit card.

BASICS

A smart card is a plastic card with a microprocessor chip embedded

in it. The card looks like a normal credit card except for its metal contact (in

contact card only), but applications performed could be totally different. Other

than normal credit card and bankcard functions, a smart card could act as an

electronic wallet where electronic cash is kept. With the appropriate software, it

could also be used as a secure access control token ranging from door access

control to computer authentication.

The term “smart card” has different meanings in different books

[Guthery1998, Rankl1997] because smart cards have been used in different

applications.

SMART CARD

The smart card is defined as a “Credit Card” with a “Brain” on it, the

brain being a small Embedded Computer Chip. Because of this “Embedded

Brain”, smart card is also known as chip or integrated circuit (IC) card. Some

types of smart card may have a microprocessor embedded, while others may only

have a non-volatile memory content included. In general, a plastic card with a

chip embedded inside can be considered as a smart card.

In either type of smart card, the storage capacity of its memory content is

much larger than that in magnetic stripe cards. The total storage capacity of a

magnetic stripe card is 125 bytes while the typical storage capacity of a smart card

ranges from 1K bytes to 64K bytes. In other words, the memory content of a large

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capacity smart card can hold the data content of more than 500 magnetic stripe

cards.

Obviously, large storage capacity is one of the advantages in using smart

card, but the single-most important feature of smart card consists of the fact that

their stored data can be protected against unauthorized access and tampering.

Inside a smart card, access to the memory content is controlled by a secure logic

circuit within the chip. As access to data can only is performed via a serial

interface supervised by the operating system and the secure logic system,

confidential data written onto the card is prevented from unauthorized external

access. This secret data can only be processed internally by the microprocessor.

Due to the high security level of smart cards and its off-line nature, it is

extremely difficult to “hack” the value off a card, or otherwise put unauthorized

information on the card. Because it is hard to get the data without authorization,

and because it fits in one’s pocket, a smart card is uniquely appropriate for secure

and convenient data storage. Without permission of the card holder, data could not

be captured or modified. Therefore, smart card could further enhance the data

privacy of user.

Therefore, smart card is not only a data store, but also programmable,

portable, tamper-resistant memory storage.

SMART CARD READER

Smart Card Readers are also known as Card Programmers (because they

can write to a card), card terminals, card acceptance device (CAD) or an interface

device (IFD). When the smart card and the card reader come into contact, each

identifies itself to the other by sending and receiving information. If the messages

exchanged do not match, no further processing takes place.

Smart Card Reader Working

Smart Card Readers are also known as card programmers (because they

can write to a card), card terminals, card acceptance device (CAD) or an interface

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device (IFD). There is a slight difference between the card reader and the

terminal. The term ‘reader’ is generally used to describe a unit that interfaces with

a PC for the majority of its processing requirements. In contrast, a ‘terminal’ is a

self-contained processing device.

The reader provides a path for your application to send and receive

commands from the card. There are many types of readers available, such as

serial, PC Card, and standard keyboard models. Unfortunately, the ISO group was

unable to provide a standard for communicating with the readers so there is no

one-size-fits-all approach to smart card communication.

Each manufacturer provides a different protocol for communication with the

reader.

First you have to communicate with the reader.

Second, the reader communicates with the card, acting as the intermediary

before sending the data to the card.

Third, communication with a smart card is based on the APDU format. The

card will process the data and return it to the reader, which will then return the

data to its originating source.

The following classes are used for communicating with the reader:

ISO command classes for communicating with 7816 protocol

Classes for communicating with the reader

Classes for converting data to a manufacturer-specific format

An application for testing and using the cards for an intended and specific

purpose

Communicating with a Smart Card Reader

The reader provides a path for your application to send and receive commands

from the card. There are many types of readers available, such as serial, PC Card,

and standard keyboard models. Unfortunately, the ISO group was unable to

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provide a standard for communicating with the readers so there is no one-size-fits-

all approach to smart card communication.

Each manufacturer provides a different protocol for communication with the

reader.

First you have to communicate with the reader.

Second, the reader communicates with the card, acting as the intermediary

before sending the data to the card.

Third, communication with a smart card is based on the APDU format. The

card will process the data and return it to the reader, which will then return

the data to its originating source.

HISTORY

A Card embedded with a microprocessor was first invented by 2

German engineers in 1967. It was not publicized until Roland Moreno, a French

journalist, announced the Smart Card patent in France in 1974 [Rankl1997].

With the advances in microprocessor manufacturing technology, the development

cost of the smart card has been greatly reduced. In 1984, a breakthrough was

achieved when French Postal and Telecommunications services (PTT)

successfully carried out a field trial with telephone cards. Since then, smart cards

are no longer tied to the traditional bankcard market even though the phone card

market is still the largest market of smart cards in 1997.

Due to the establishment of the ISO-7816 specification in 1987 (a worldwide

smart card interface standard), the smart card format is now standardized.

Nowadays, smart cards from different vendors could communicate with the host

machine using a common set of language.

TYPES

According to the definitions of “smart card” in the Smart card technology],

the word smart card has three different meanings:

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IC card with ISO 7816 interface

Processor IC card

Personal identity token containing Ics

Basically, based on their physical characteristics, IC cards can be

categorized into 4 main types, memory card, contact CPU card, contact-less card

and combi card.

Memory Cards

A memory card is a card with only memory and access logic onboard.

Similar to the magnetic stripe card, a memory card can only be used for

data storage. No data processing capability should be expected. Without

the on-board CPU, memory cards use a synchronous communication

mechanism between the reader and the card where the communication

channel is always under the direct control of the card reader. Data stored

on the card can be retrieved with an appropriate command to the card.

In traditional memory cards, no security control logic is included.

Therefore, unauthorized access to the memory content on the card could not be

prevented. While in current memory cards, with the security control logic

programmed on the card, access to the protection zone is restricted to users with

the proper password only.

Contact CPU Cards

A more sophisticated version of smart card is the contact CPU card. A

microprocessor is embedded in the card. With this real “brain”, program stored

inside the chip can be executed. Inside the same chip, there are four other

functional blocks: the mask-ROM, Non-volatile memory, RAM and I/O port

[HKSAR1997, Rankl1997].

Except for the microprocessor unit, a memory card contains almost all

components that are included in a contact CPU card. Both of them consist of Non-

volatile memory, RAM, ROM and I/O unit. Based on ISO 7816 specifications, the

external appearance of these contact smart cards is exactly the same. The only

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difference is the existence of the CPU and the use of ROM. In the CPU card,

ROM is masked with the chip’s operating system which executes the commands

issued by the terminal, and returns the corresponding results. Data and application

program codes are stored in the non-volatile memory, usually EEPROM, which

could be modified after the card manufacturing stage.

One of the main features of a CPU card is security. In fact, contact CPU card

has been mainly adopted for secure data transaction. If a user could not

successfully authenticate him/herself to the CPU, data kept on the card could not

be retrieved. Therefore, even when a smart card is lost, the data stored inside the

card will not be exposed if the data is properly stored. Also, as a secure portable

computer, a CPU card can process any internal data securely and outputs the

calculated result to the terminal.

Contact less Cards

Contact less smart card is the one in which the chip communicates with the card

reader through RFID induction technology (at data rates of 106 – 848 Kbits/sec).

These cards require only close proximity to an antenna to complete transaction.

They are often used when transactions must be processed quickly or hands-free,

such as on mass transit systems, where smart cards can be used without even

removing them from a wallet.

Even though contact CPU smart card is more secure than

memory card, it may not be suitable for all kinds of applications, especially where

massive transactions are involved, such as transportation uses. Because in public

transport uses, personal data must be captured by the reader within a short period

of time, contact smart card which requires the user to insert the card to the reader

before the data can be captured from the card would not be a suitable choice.

With the use of radio frequency, the contact-less smart card can transmit user data

from a fairly long distance within a short activation period. The card holder would

not have to insert the card into the reader. The whole transaction process could be

performed without removing the card from the user’s wallet.

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Contact-less smart cards use a technology that enables card readers to provide

power for transactions and communications without making physical contact with

the cards. Usually electromagnetic signal is used for communication between the

card and the reader. The power necessary to run the chip on the card could either

be supplied by the battery embedded in the card or transmitted at microwave

frequencies from the reader onto the card.

Contact-less card is highly suitable for large quantity of card access and data

transaction. However, contact-less smart card has not been standardized. There

are about 16 different contacts-less card technologies and card types in the market

[ADE]. Each of these cards has its specific advantages, but they may not be

compatible with each other. Nevertheless, because of its high production cost and

the technology is relatively new, this type of cards has not been widely adopted.

Combi-Card

At the current stage, contact and contact-less smart card are using two

different communication protocols and development processes. Both cards

have their advantages and disadvantages. Contact smart cards have higher

level of security and readily-available infrastructure, while contact-less

smart card provide a more efficient and convenient transaction

environment. In order to provide customers with the advantages of these

two cards, two methods could be employed. The first method is to build a

hybrid card reader, which could understand the protocols of both types of

cards. The second method is to create a card that combines the contact

functions with the contactless functions. Because the manufacturing cost

of the hybrid reader is very expensive, the later solution is usually chosen.

Sometimes, the term “combi card” is being misused by manufacturers. In

general, there are two types of combine contact-contactless smart cards, namely

the hybrid card and the combi card. Both cards have contact and contactless parts

embedded together in the plastic card. However, in the hybrid card, the contact IC

chip and contactless chip are separate modules. No electrical connections have

been included for communications between the two chips. These two modules can

be considered as separate but co-existing chips on the same card. While in the

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combi card, the contact and contactless chips could communicate between

themselves, thus giving the combi card the capability to talk with external

environment via either the contact or contactless method.

As the combi cards possess the advantages of both contact and contactless

cards, the only reason that is hindering its acceptance is cost. When the cost and

technical obstacles are overcome, combi cards will become a popular smart card

solution.

In our project the Smart Card used is of the type Contact type cards.

Basically this type of Smart Cards got SIM like Structure Embedded on a Plastic

card for Physical Structure and Strength. There exist different types of SIM

structures according to the type of Application, Memory and features involved in

the Smart Card. Some of them are shown below.

FIG 23 :Types of SIM Structures

These Contact type Smart cards have a contact area, comprising several gold-

plated contact pads, that is about 1cm square. When inserted into a reader, the

chip makes contact with electrical connectors that can read information from the

chip and write information back.

Electrical signals description

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FIG 24 : Smart Card pin-out

VCC: Power supply input

RST: Either used it (reset signal supplied from the interface device) or in

combination with an internal reset control circuit (optional use by the card). If

internal reset is implemented, the voltage supply on Vcc is mandatory.

CLK: Clocking or timing signal (optional use by the card).

GND: Ground (reference voltage).

VPP: Programming voltage input (deprecated / optional use by the card).

I/O: Input or Output for serial data to the integrated circuit inside the card.

Contact type Smart Card Reader

Contact smart card readers are used as a communications medium between the

smart card and a host, e.g. a computer, a point of sale terminal, or a mobile

telephone.

Since the chips in the financial cards are the same as those used for mobile phone

Subscriber Identity Module (SIM) cards, just programmed differently and

embedded in a different shaped piece of PVC, the chip manufacturers are building

to the more demanding GSM/3G standards. So, for instance, although EMV

allows a chip card to draw 50 mA from its terminal, cards are normally well inside

the telephone industry’s 6mA limit. This is allowing financial card terminals to

become smaller and cheaper.

The reader provides a path for your application to send and receive commands

from the card. There are many types of readers available, such as serial, PC-Card,

83

and standard keyboard models. Unfortunately, the ISO group was unable to

provide a standard for communicating with the readers so there is no one-size-fits-

all approach to smart card communication.

Each manufacturer provides a different protocol for communication with the

reader.

First you have to communicate with the reader.

Second, the reader communicates with the card, acting as the intermediary

before sending the data to the card.

Third, communication with a smart card is based on the APDU format. The

card will process the data and return it to the reader, which will then return the

data to its originating source.

The following classes are used for communicating with the reader:

ISO command classes for communicating with 7816 protocol

Classes for communicating with the reader

Classes for converting data to a manufacturer-specific format

An application for testing and using the cards for an intended and specific

purpose

Readers come in many forms, factors and capabilities. The easiest way to describe

a reader is by the method of its interface to a PC. Smart card readers are available

that interface to RS232 serial ports, USB ports, PCMCIA slots, floppy disk slots,

parallel ports, infrared IRDA ports and keyboards and keyboard wedge readers.

Card readers are used to read data from – and write data to – the smart card.

Readers can easily be integrated into a PC utilizing Windows 98/Me, 2000, or XP

platforms. However, some computer systems already come equipped with a built-

in smart card reader. Some card readers come with advanced security features

such as secure PIN entry, secure display and an integrated fingerprint scanners for

the next-generation of multi-layer security and three-factor authentication.

Another difference in reader types is on-board intelligence and capabilities. An

extensive price and performance difference exists between an industrial strength

reader that supports a wide variety of card protocols and the less expensive win-

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card reader that only works with microprocessor cards and performs all

processing of the data in the PC.

The options in terminal choices are just as varied. Most units have their own

operating systems and development tools. They typically support other functions

such as magnetic-stripe reading, modem functions and transaction printing.

To process a smart card the computer has to be equipped with a smart card reader

possessing the following mandatory features:

Smart Card Interface Standard – ISO 7816 is an international standard that

describes the interface requirements for contact-type smart cards. These standards

have multiple parts. For instance, part 1, 2 and 3 are applicable to card readers.

Part 1 defines the physical characteristics of the card. Part 2 defines dimension

and location of smart card chip contacts. Part 3 defines the electronic signals and

transmission protocols of the card. Card readers may be referred to as conforming

to ISO 7816 1/2/3, or in its simplified term, ISO 7816.

Driver – This refers to the software used by the operating system (OS) of a

PC for managing a smart card and applicable card reader. To read a smart ID card,

the driver of the card reader must be PC/SC compliant which is supported by most

card reader products currently available. It should be noted that different OS

would require different drivers. In acquiring card readers, the compatibility

between the driver and the OS has to be determined and ensured.

Desirable Features in a Smart Card Reader:

Card Contact Types refers to how the contact between a card reader and a

smart card is physically made. There are two primary types of contact: landing

contact and friction contact (also known as sliding or wiping). For card readers

featuring friction contact, the contact part is fixed. The contact wipes on the card

surface and the chip when a card is inserted. For card readers featuring the landing

type, the contact part is movable. The contact “lands” on the chip after a card is

wholly inserted. In general, card readers of the landing type provide better

protection to the card than that of the friction type.

Smart card readers are also used as smart card programmers to configure

and personalize integrated circuit cards. These programmers not only read data,

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but also put data into the card memory. This means that not only CPU based smart

cards, but also simple memory cards can be programmed using a smart card

reader. Of course the card reader must support the appropriate protocol such as the

asynchronous T=0, T=1 or synchronous I2C protocols.

The smart card reader here in this project used is the supports the T=0, T=1

protocols. The smart card here used is of 256 bytes of memory (SLE 4442). The

following section gives the some sort of information about the smart card memory

and its interfacing commands.

Features:

256 ´ 8-bit EEPROM organization

Byte-wise addressing

Irreversible byte-wise write protection of lowest 32 addresses (Byte 0 ...

31)

32 ´ 1-bit organization of protection memory

Two-wire link protocol

End of processing indicated at data output

Answer-to-Reset acc. To ISO standard 7816-3

Programming time 2.5 ms per byte for both erasing and writing

Minimum of 104 write/erase cycles1)

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COMMUNICATION PROTOCOLS

Name Description

T=0 Asynchronous half-duplex byte-level transmission protocol.

T=1 Asynchronous half-duplex block-level transmission protocol.

T=2 Reserved for future full-duplex operations.

T=3 Reserved for future full-duplex operations.

T=CL APDU transmission via contactless interface ISO 14443.

Data retention for minimum of ten years1)

Contact configuration and serial interface in accordance with ISO standard

7816 (synchronous transmission)

Pin configuration:

Pin description:

COMMAND SET FOR SLE4442– 256 bytes Memory

Steps Command Comd to SR90 Prompt from SR90 Reader

1. Set Device Type #0203! #83! (Positive Ack)

#8A! (Invalid Device Type set)

2. Send Card Status #01! #80! (Card Present)

#81! (Card Absent)

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3. ATR #03! #88A2131091!

4. Read Data #10AANN! #87AANNDDD…D!

(DDD = Data)

#86! (Invalid Command)

#82! (No Device Type set)

#8D! (Memory Over Flow)

5. Write Data #11AANNFFFFFF

DD..D! #82! (No Device Type set )

#83! (Positive Ack)

#89! (Invalid Security Code)

#86! (Invalid Command)

#85! (Invalid Parameters

#8D! (Memory over Flow)

#90!(Already Protected)

6. Protect Data #12AANNFFFFFF

DD! #83! (Positive Ack)

#82! (No Device Type)

#89! (Invalid Security Code)

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#86! (Invalid Command)

#85! (Invalid Parameters

#8D! (Memory Over Flow)

7. Change Security Code #53FFFFFF555555 #83! (Positive Ack)

#89! (Invalid Security Code)

#86! (Invalid Command)

#85! (Invalid Parameters

8. Locations Which can’t write : 0,1,2,3,6,7

9. Communication Protocol: Baud Rate :9,600 bps

Parity :None

Stop Bit :1

Start Bit :0

Data :8 bits

AA = Address location of the chip in Hex

NN = Number of bytes to read or to write

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FFFFFF = Security Code

DD = Data to read /write or protect in BCD format

Note: Please give correct security code while writing your cards other wise

they will damage. This card will allow 3 times of writing false security code

later it won’t accept to write the card but you can read.

In our project, the Smart Card Reader communicates with microcontroller

through 2 pins namely RX and TX with the help of a Serial Driver. These 2 pins

are pin 2, 3 of the 9-pin connector of Smart Card Reader.

Fig 25 :SMART CARD READER

APPLICATIONS

With the rapid expansion of Internet technology and

electronic commerce, smart cards are now more widely accepted in the

commercial market as stored-value and secure storage cards. Moreover, it has also

been widely used as an identity card.

The smart card has also been used in transportation such as

the Octopus card which has been adopted by the MTRC and KCRC to replace of

the old Magnetic stripe card. Medical record can also be stored in the smart card.

This enables critical information of the patient to be retrieved whenever it is

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required. With the help of smart card technology, many secure data such as the

computer login name and password can also be kept, so user need not remember a

large number of passwords.

The applications can be classified into 6 main categories: Electronic

Payment, Security and Authentication, Transportation, Telecommunications,

Loyalty Program and Health Care Applications.

1. ELECTRONIC PAYMENT

Electronic Purse

Electronic Purse is also known as electronic cash. Funds can be loaded onto a

card for use as cash. The electronic cash can be used for small purchases without

necessarily requiring the authorization of a PIN. The card is credited from the

cardholder’s bank account or some other ways. When it is used to purchase goods

or services, electronic value is deducted from the card and transferred to the

retailer’s account. Similar to a real wallet, the cardholder could credit his/her card

at the bank any time when required.

Stored Value Cards

Another use of smart cards in electronic commerce is Electronic token. It is an

example of the stored-value card. The principle is that some memory in the smart

card is set aside to store electronic tokens or electronic tickets. A smart card can

store tokens for different services and each of the tokens can be refilled,

depending on the types of the memory card. This allows the cost to be distributed

over a number of services and over a much longer life span.

For example, the card could be used to pay for gas and instead of putting coins in

a parking meter. Consumers load up the card from a vending machine.

2. SECURITY AND AUTHENTICATION

Cryptographic uses

From the point-of-view of the supplier and system operator, the main

requirement of almost all machine-readable card systems is to ensure that the card

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presented is valid and the cardholder is indeed the person entitled to use that

particular card. To verify the cardholder’s identity, users are required to enter their

PIN code (personal identification number). This PIN code is kept in the card

rather than on the terminals or host machines.

Identification and authentication procedures take place at the card terminal.

Identity card

The identification of an individual is one of the most complex processes in

the field of Information Technology. It requires both the individual to identify

himself and for the system to recognize the incoming connection is generated by a

legal user. The system then accepts responsibility for allowing all subsequent

actions, sage in the knowledge that the user has authorization to do whatever he is

asking of the system.

If a smart card is used, the information stored on the card can be verified locally

against a ‘password’ or PIN before connection is made to the host. This prevents

the password from being eavesdropped by perpetrators on the Internet.

Some of the smart cards will have personal data stored on the card. For example,

the cardholder’s name, ID number, and date of birth

Access control card

The most common devices used to control access to private areas where

sensitive work is being carried out or where data is held, are keys, badges and

magnetic cards. These all have the same basic disadvantages: they can easily be

duplicated and when stolen or passed on, they can allow entry by an unauthorized

person. The smart card overcomes these weaknesses by being very difficult to be

reproduced and capable of storing digitized personal characteristics. With suitable

verification equipment, this data can be used at the point of entry to identify

whether the user is the authorized cardholder. The card can also be individually

personalized to allow access to limited facilities, depending on the holder’s

security clearance. A log of the holder’s movements, through a security system,

can be stored on the card as a security audit trail

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Digital certificate

The most important security measures we encounter in our daily business

have nothing to do with locks and guards. A combination of a signed message and

the use of public key cryptosystem, so called digital signature, are typically used.

A digitally signed message containing a public key is called a certificate. In

addition to a public key, a certificate typically contains a name, address, and other

information describing the holder of the corresponding secret key. All of these

carry the digital signature of a registry service that records public keys for all

members of the community. To become a member of this community, a

subscriber must do two things:

Provide the directory service with a public key and the associated

identification information so that other people will be able to verify his/her

signature.

Obtain the public key of the directory service so that he/she can verify

other people’s signatures.

Because certificates are extremely tamper resistant, the authenticity of a

certificate is a property of the certificate itself, rather than of the authenticity of

the channel over which it was received.

Computer login

Access to the Computer room and its services can be controlled by the

smart card. In terms of network access, smart card can authenticate the user to the

host.

Furthermore, depending on the environment being protected the network access

card can also perform the following functions:

Manipulation of different authentication codes for different levels of

security.

Use of biometric techniques as an added security measure.

Maintaining an audit trail of failures and attempted violations.

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Meanwhile, in terms of access to the computer room itself, PIN checking can

be done on the card without the need for hard wiring the access points to a central

computer.

The identification of a user is usually done by means of a (Personal Identification

Number) PIN. The PIN is verified by the microcomputer of the card with the PIN

stored in its RAM. If the comparison is negative, the CPU will refuse to work.

The chip also keeps tack of the number of consecutive wrong PIN entries. If this

number reaches a pre-set threshold, the card blocks itself against any further use.

TRANSPORTATION APPLICATIONS

The smart card can act as electronic money for car drivers who would need

to pay a fee before being able to use a road or tunnel. It would then contain a

balance that can be increased at payment stations or in the pre-paid process, and is

decreased for each use.

TELECOMMUNICATION APPLICATIONS

Since 1988, smart card has become an essential component in cellular

phone systems. Network data, subscriber’s information and all mobile network

critical data are kept inside the card. With this card, subscribers could make calls

from any portable telephone. Moreover, through the IC card, any calls through the

mobile phone could be encrypted, and thus ensure privacy. In the future, more and

more value-added services, such as electronic banking, could be supported by

using this microprocessor card.

HEALTH CARE APPLICATIONS

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Due to the level of security provided for data storage, IC cards offer a new

perspective for healthcare applications. Medical applications of smart cards can be

used for storing information including personal data, insurance policy, emergency

medical information, hospital admission data and recent medical records.

LOYALTY APPLICATIONS

Loyalty program is another important application of smart cards in the

shopping model. The preferred customer status together with detailed information

on shopping habits is stored and processed on the smart card. With this

information, merchants could derive better shopping model or tailor-make

personalized customer shopping profiles. In addition, this shopping habit profile is

kept in the customer’s card; therefore, his/her shopping record could be kept

confidential from unauthorized access.

ENERGY METER

The Energy Meter is a device which takes the 230 V ac input supply and gives out

the same. In other words it just acts as mediator which takes and gives out the

same but it calculates the number of units of energy being consumed. It monitors

the power consumed with respect to time.

In this project this Energy meter is also connected through a Relay to either

switch it ON or OFF according to the balance available in the Smart card being

inserted.

OPTO COUPLERS:

There are many situations where signals and data need to be transferred

from one system to another within a piece of electronics equipment, or from one

piece of equipment to another, without making a direct ëohmicí electrical

connection. Often this is because the source and destination are (or may be at

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times) at very different voltage levels, like a microprocessor which is operating

from 5V DC but being used to control a triac which is switching 240V AC. In

such situations the link between the two must be an isolated one, to protect the

microprocessor from over voltage damage. Relays can of course provide this kind

of isolation, but even small relays tend to be fairly bulky compared with ICs and

many of todayís other miniature circuit components. Because theyíre electro-

mechanical, relays are also not as reliable ó and only capable of relatively low

speed operation. Where small size, higher speed and greater reliability are

important, a much better alternative is to use an opt coupler. These use a beam of

light to transmit the signals or data across an electrical barrier, and achieve

excellent isolation.

Optocouplers typically come in a small 6-pin or 8-pin IC package, but are

essentially a combination of two distinct devices: an optical transmitter, typically

a gallium arsenide LED (light-emitting diode) and an optical receiver such as a

phototransistor or light-triggered diac. The two are separated by a transparent

barrier which blocks any electrical current flow between the two, but does allow

the passage of light. The basic idea is shown in Fig.1, along with the usual circuit

symbol for an optocoupler. Usually electrical connections to the LED section are

brought out to the pins on one side of the package and those for the

phototransistor or diac to the other side, to physically separate them as much as

possible. This usually allows Optocouplers to withstand voltages of anywhere

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between 500V and 7500V between input and output. Optocouplers are essentially

digital or switching devices, so they’re best for transferring either on-off control

signals or digital data. Analog signals can be transferred by means of frequency or

pulse-width modulation.

Key Parameters

The most important parameter for most Optocouplers is their transfer

efficiency, usually measured in terms of their current transfer ratio or CTR. This

is simply the ratio between a current change in the output transistor and the

current change in the input LED which produced it. Typical values for CTR range

from 10% to 50% for devices with an output phototransistor and up to 2000% or

so for those with a Darlington transistor pair in the output. Note, however that in

most devices CTR tends to vary with absolute current level. Typically it peaks at a

LED current level of about 10mA, and falls away at both higher and lower current

levels.

RELAYS

Relay is an electrically operated switch. Current flowing through the coil of the

relay creates a magnetic field which attracts a lever and changes the switch

contacts. The coil current can be on or off so relays have two switch positions and

they are double throw (changeover) switches.

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Relays allow one circuit to switch a second circuit which can be

completely separate from the first. For example a low voltage battery circuit can

use a relay to switch a 230V AC mains circuit. There is no electrical connection

inside the relay between the two circuits; the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a

12V relay, but it can be as much as 100mA for relays designed to operate from

lower voltages. Most ICs (chips) cannot provide this current and a transistor is

usually used to amplify the small IC current to the larger value required for the

relay coil. The maximum output current for the popular 555 timer IC is 200mA so

these devices can supply relay coils directly without amplification.

Relays are usually SPDT or DPDT but they can have many more sets of

switch contacts, for example relays with 4 sets of changeover contacts are readily

available. For further information about switch contacts and the terms used to

describe them please see the page on switches.

Most relays are designed for PCB mounting but you can solder wires

directly to the pins providing you take care to avoid melting the plastic case of the

relay. The supplier's catalogue should show you the relay's connections. The coil

will be obvious and it may be connected either way round. Relay coils produce

brief high voltage 'spikes' when they are switched off and this can destroy

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transistors and ICs in the circuit. To prevent damage you must connect a

protection diode across the relay coil.

The animated picture shows a working relay with its coil and switch

contacts. You can see a lever on the left being attracted by magnetism when the

coil is switched on. This lever moves the switch contacts. There is one set of

contacts (SPDT) in the foreground and another behind them, making the relay

DPDT.

The relay's switch connections are usually labelled COM,

NC and NO:

COM = Common, always connect to this, it is the moving part of the

switch.

NC = Normally Closed, COM is connected to this when the relay coil is

off.

NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when

the relay coil is on.

Connect to COM and NC if you want the switched circuit to be on when

the relay coil is off.

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Choosing a relay

You need to consider several features when choosing a relay:

1. Physical size and pin arrangement If you are choosing a relay for an

existing PCB you will need to ensure that its dimensions and pin

arrangement are suitable. You should find this information in the supplier's

catalogue.

2. Coil voltage the relay's coil voltage rating and resistance must suit the

circuit powering the relay coil. Many relays have a coil rated for a 12V

supply but 5V and 24V relays are also readily available. Some relays

operate perfectly well with a supply voltage which is a little lower than

their rated value.

3. Coil resistance the circuit must be able to supply the current required by the

relay coil. You can use Ohm's   law to calculate the current:

Relay coil current   =   supply voltage 

  coil resistance

4. For example: A 12V supply relay with a coil resistance of 400 passes a

current of 30mA. This is OK for a 555 timer IC (maximum output current

200mA), but it is too much for most ICs and they will require a transistor

to amplify the current.

5. Switch ratings (voltage and current) the relay's switch contacts must be

suitable for the circuit they are to control. You will need to check the

voltage and current ratings. Note that the voltage rating is usually higher

for AC, for example: "5A at 24V DC or 125V AC".

6. Switch contact arrangement (SPDT, DPDT etc).

Most relays are SPDT or DPDT which are often described as "single pole

changeover" (SPCO) or "double pole changeover" (DPCO). For further

information please see the page on switches

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Protection diodes for relays

Transistors and ICs (chips) must be protected from the brief high voltage 'spike'

produced when the relay coil is switched off. The diagram shows how a signal

diode (eg 1N4148) is connected across the relay coil to provide this protection.

Note that the diode is connected 'backwards' so that it will normally not conduct.

Conduction only occurs when the relay coil is switched off, at this moment

current tries to continue flowing through the coil and it is harmlessly diverted

through the diode. Without the diode no current could flow and the coil would

produce a damaging high voltage 'spike' in its attempt to keep the current flowing.

Reed relays

Reed relays consist of a coil surrounding a reed switch.

Reed switches are normally operated with a magnet, but in

a reed relay current flows through the coil to create a magnetic field and close the

reed switch.

Reed relays generally have higher coil resistances than standard relays

(1000 for example) and a wide range of supply voltages (9-20V for example).

They are capable of switching much more rapidly than standard relays, up to

several hundred times per second; but they can only switch low currents (500mA

maximum for example).

Relays and transistors compared

Like relays, transistors can be used as an electrically operated switch. For

switching small DC currents (< 1A) at low voltage they are usually a better choice

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than a relay. However transistors cannot switch AC or high voltages (such as

mains electricity) and they are not usually a good choice for switching large

currents (> 5A). In these cases a relay will be needed, but note that a low power

transistor may still be needed to switch the current for the relay's coil! The main

advantages and disadvantages of relays are listed below:

Advantages of relays:

Relays can switch AC and DC, transistors can only switch DC.

Relays can switch high voltages, transistors cannot.

Relays are a better choice for switching large currents (> 5A).

Relays can switch many contacts at once.

Disadvantages of relays:

Relays are bulkier than transistors for switching small currents.

Relays cannot switch rapidly (except reed relays), transistors can switch

many times per second.

Relays use more power due to the current flowing through their coil.

Relays require more current than many chips can provide, so a low

power transistor may be needed to switch the current for the relay's coil.

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SOFTWARE DESCRIPTION

ABOUT SOFTWARE

Software used:*Keil software for c programming

ABOUT KEIL SOFTWARE:

It is possible to create the source files in a text editor such as Notepad, run the Compiler on each C source file, specifying a list of controls, run the Assembler on each Assembler source file, specifying another list of controls, run either the Library Manager or Linker (again specifying a list of controls) and finally running the Object-HEX Converter to convert the Linker output file to an Intel Hex File. Once that has been completed the Hex File can be downloaded to the target hardware and debugged. Alternatively KEIL can be used to create source files; automatically compile, link and covert using options set with an easy to use user interface and finally simulate or perform debugging on the hardware with access to C variables and memory. Unless you have to use the tolls on the command line, the choice is clear. KEIL Greatly simplifies the process of creating and testing an embedded application.

Projects:

The user of KEIL centers on “projects”. A project is a list of all the source files required to build a single application, all the tool options which specify exactly how to build the application, and – if required – how the application should be simulated. A project contains enough information to take a set of source files and generate exactly the binary code required for the application. Because of the high degree of flexibility required from the tools, there are many options that can be set to configure the tools to operate in a specific manner. It would be tedious to have to set these options up every time the application is being built; therefore they are stored in a project file. Loading the project file into KEIL informs KEIL which source files are required, where they are, and how to configure the tools in the correct way. KEIL can then execute each tool with the correct options. It is also possible to create new projects in KEIL. Source files are added to the project and the tool options are set as required. The project can then

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be saved to preserve the settings. The project is reloaded and the simulator or debugger started, all the desired windows are opened. KEIL project files have the extension

Simulator/Debugger:

The simulator/ debugger in KEIL can perform a very detailed simulation of a micro controller along with external signals. It is possible to view the precise execution time of a single assembly instruction, or a single line of C code, all the way up to the entire application, simply by entering the crystal frequency. A window can be opened for each peripheral on the device, showing the state of the peripheral. This enables quick trouble shooting of mis-configured peripherals. Breakpoints may be set on either assembly instructions or lines of C code, and execution may be stepped through one instruction or C line at a time. The contents of all the memory areas may be viewed along with ability to find specific variables. In addition the registers may be viewed allowing a detailed view of what the microcontroller is doing at any point in time.

The Keil Software 8051 development tools listed below are the programs you use to compile your C code, assemble your assembler source files, link your program together, create HEX files, and debug your target program. µVision2 for Windows™ Integrated Development Environment: combines Project Management, Source Code Editing, and Program Debugging in one powerful environment.

C51 ANSI Optimizing C Cross Compiler: creates relocatable object modules from your C source code,

A51 Macro Assembler: creates relocatable object modules from your 8051 assembler source code,

BL51 Linker/Locator: combines relocatable object modules created by the compiler and assembler into the final absolute object module,

LIB51 Library Manager: combines object modules into a library, which may be used by the linker,

OH51 Object-HEX Converter: creates Intel HEX files from absolute object modules.

What's New in µVision3?µVision3 adds many new features to the Editor like Text Templates, Quick Function Navigation, and Syntax Coloring with brace high lighting Configuration Wizard for dialog based startup and debugger setup. µVision3 is fully compatible to µVision2 and can be used in parallel with µVision2.

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What is µVision3?µVision3 is an IDE (Integrated Development Environment) that helps you write, compile, and debug embedded programs. It encapsulates the following components:

A project manager. A make facility. Tool configuration. Editor. A powerful debugger.

To help you get started, several example programs (located in the \C51\Examples, \C251\Examples, \C166\Examples, and \ARM\...\Examples) are provided.

HELLO is a simple program that prints the string "Hello World" using the Serial Interface.

MEASURE is a data acquisition system for analog and digital systems. TRAFFIC is a traffic light controller with the RTX Tiny operating system. SIEVE is the SIEVE Benchmark. DHRY is the Dhrystone Benchmark. WHETS is the Single-Precision Whetstone Benchmark.

Additional example programs not listed here are provided for each device architecture.

Building an Application in µVision2To build (compile, assemble, and link) an application in µVision2, you must:

1. Select Project -(forexample,166\EXAMPLES\HELLO\HELLO.UV2).2. Select Project - Rebuild all target files or Build target.

µVision2 compiles, assembles, and links the files in your project

Creating Your Own Application in µVision2 To create a new project in µVision2, you must:

1. Select Project - New Project.2. Select a directory and enter the name of the project file.3. Select Project - Select Device and select an 8051, 251, or C16x/ST10

device from the Device Database™.4. Create source files to add to the project.5. Select Project - Targets, Groups, Files. Add/Files, select Source Group1,

and add the source files to the project.6. Select Project - Options and set the tool options. Note when you select the

target device from the Device Database™ all special options are set automatically. You typically only need to configure the memory map of your target hardware. Default memory model settings are optimal for most applications.

105

7. Select Project - Rebuild all target files or Build target.Debugging an Application in µVision2To debug an application created using µVision2, you must:

1. Select Debug - Start/Stop Debug Session.2. Use the Step toolbar buttons to single-step through your program. You may

enter G, main in the Output Window to execute to the main C function.3. Open the Serial Window using the Serial #1 button on the toolbar.

Debug your program using standard options like Step, Go, Break, and so on.

Starting µVision2 and Creating a Project

µVision2 is a standard Windows application and started by clicking on the program icon. To create a new project file select from the µVision2 menu

Project – New Project…. This opens a standard Windows dialog that asks you

for the new project file name.

We suggest that you use a separate folder for each project. You can simply use

the icon Create New Folder in this dialog to get a new empty folder. Then

select this folder and enter the file name for the new project, i.e. Project1.

µVision2 creates a new project file with the name PROJECT1.UV2 which contains

a default target and file group name. You can see these names in the Project

Window – Files.

Now use from the menu Project – Select Device for Target and select a CPU

for your project. The Select Device dialog box shows the µVision2 device

database. Just select the micro controller you use. We are using for our examples the Philips 80C51RD+ CPU. This selection sets necessary tool

options for the 80C51RD+ device and simplifies in this way the tool Configuration

Building Projects and Creating a HEX Files

Typical, the tool settings under Options – Target are all you need to start a new

application. You may translate all source files and line the application with a

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click on the Build Target toolbar icon. When you build an application with

syntax errors, µVision2 will display errors and warning messages in the Output

Window – Build page. A double click on a message line opens the source file

on the correct location in a µVision2 editor window.

Once you have successfully generated your application you can start debugging.

After you have tested your application, it is required to create an Intel HEX file to download the software into an EPROM programmer or simulator. µVision2 creates HEX files with each build process when Create HEX files under Options for Target – Output is enabled. You may start your PROM programming utility after the make process when you specify the program under the option Run User Program #1.

CPU Simulation:

µVision2 simulates up to 16 Mbytes of memory from which areas can be

mapped for read, write, or code execution access. The µVision2 simulator traps

and reports illegal memory accesses.

In addition to memory mapping, the simulator also provides support for the

Integrated peripherals of the various 8051 derivatives. The on-chip peripherals

of the CPU you have selected are configured from the Device.

Database selection:

you have made when you create your project target. Refer to page 58 for more

Information about selecting a device. You may select and display the on-chip peripheral components using the Debug menu. You can also change the aspects of each peripheral using the controls in the dialog boxes.

Start Debugging:

You start the debug mode of µVision2 with the Debug – Start/Stop Debug

Session command. Depending on the Options for Target – Debug

Configuration, µVision2 will load the application program and run the startup

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code µVision2 saves the editor screen layout and restores the screen layout of the last debug session. If the program execution stops, µVision2 opens an

editor window with the source text or shows CPU instructions in the disassembly window. The next executable statement is marked with a yellow arrow. During debugging, most editor features are still available.

For example, you can use the find command or correct program errors. Program source text of your application is shown in the same windows. The µVision2 debug mode differs from the edit mode in the following aspects:

_ The “Debug Menu and Debug Commands” described on page 28 are

Available. The additional debug windows are discussed in the following.

_ The project structure or tool parameters cannot be modified. All build

Commands are disabled.

Disassembly Window

The Disassembly window shows your target program as mixed source and assembly program or just assembly code. A trace history of previously executed instructions may be displayed with Debug – View Trace Records. To enable the trace history, set Debug – Enable/Disable Trace Recording.

If you select the Disassembly Window as the active window all program step commands work on CPU instruction level rather than program source lines. You can select a text line and set or modify code breakpoints using toolbar buttons or the context menu commands.

You may use the dialog Debug – Inline Assembly… to modify the CPU instructions. That allows you to correct mistakes or to make temporary changes to the target program you are debugging.

SOFTWARE COMPONENTS

About Keil

1. Click on the Keil u Vision Icon on Desktop

2. The following fig will appear

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3. Click on the Project menu from the title bar

4. Then Click on New Project

5. Save the Project by typing suitable project name with no extension in u r own folder sited in either C:\ or D:\

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6. Then Click on Save button above.

7. Select the component for u r project. i.e. Atmel……

8. Click on the + Symbol beside of Atmel

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9. Select AT89C51 as shown below

10. Then Click on “OK”

11. The Following fig will appear

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12. Then Click either YES or NO………mostly “NO”

13. Now your project is ready to USE

14. Now double click on the Target1, you would get another option

“Source group 1” as shown in next page.

15. Click on the file option from menu bar and select “new”

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16. The next screen will be as shown in next page, and just maximize it by

double clicking on its blue boarder.

17. Now start writing program in either in “C” or “ASM”

18. For a program written in Assembly, then save it with extension “. asm”

and for “C” based program save it with extension “ .C”

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19. Now right click on Source group 1 and click on “Add files to Group Source”

20. Now you will get another window, on which by default “C” files will appear.

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21. Now select as per your file extension given while saving the file

22. Click only one time on option “ADD”

23. Now Press function key F7 to compile. Any error will appear if so

happen.

24. If the file contains no error, then press Control+F5 simultaneously.

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25. The new window is as follows

26. Then Click “OK”

27. Now Click on the Peripherals from menu bar, and check your required

port as shown in fig below

28. Drag the port a side and click in the program file.

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29. Now keep Pressing function key “F11” slowly and observe.

30. You are running your program successfully

Embedded C:

What is an embedded system?

An embedded system is an application that contains at least one

programmable computer and which is used by individuals who are, in the main,

unaware that the system is computer-based.

Which programming language should you use?

Having decided to use an 8051 processor as the basis of your embedded

system, the next key decision that needs to be made is the choice of programming

language. In order to identify a suitable language for embedded systems, we might

begin by making the following observations:

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Computers (such as microcontroller, microprocessor or DSP chips) only

accept instructions in ‘machine code’ (‘object codes’). Machine code is, by

definition, in the language of the computer, rather than that of the

programmer. Interpretation of the code by the programmer is difficult and

error prone.

All software, whether in assembly, C, C++, Java or Ada must ultimately be

translated into machine code in order to be executed by the computer.

Embedded processors – like the 8051 – have limited processor power and

very limited memory available: the language used must be efficient.

The language chosen should be in common use.

Summary of C language Features:

It is ‘mid-level’, with ‘high-level’ features (such as support for functions and

modules), and ‘low-level’ features (such as good access to hardware via pointers).

It is very efficient.

It is popular and well understood.

Even desktop developers who have used only Java or C++ can soon

understand C syntax.

Good, well-proven compilers are available for every embedded processor

(8-bit to 32-bit or more).

Basic C program structure:

//- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

//Basic blank C program that does nothing

// Includes

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//- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

#include <reg51.h> // SFR declarations

Void main (void)

{

While (1);

{

Body of the loop // Infinite loop

}

} // match the braces

ADVANTAGES:

Reduce the cost of theft and corruption on the electricity distribution

network with electronic designs and prepayment interfaces. Prepayment

meters ensure energy meters now exist that measure current in both phase

and neutral and calculate power consumption based on the larger of the two

currents. As discussed below, these solutions no longer have to be

populated with many components on a printed circuit board. Highly

integrated solutions exist to reduce cost and improve reliability.

Improve the cost and quality of electricity distribution through remote

meter reading and efficient data management. Besides reducing the cost of

manually reading meters, power outages can be detected, identified, and

corrected more quickly for customers whose meters are communicating

through a network.

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Environmental pollution is minimized by reducing the size of power

generation equipment. Peak usage is minimized despite population growth

through multiple rate billing and distribution cleanliness is maintained by

monitoring power quality pollution contributed by individual consumers.

LIMITATIONS:

Increased security risks from network or remote access

Greater potential for monitoring by other/unauthorized third parties.

The Centralized administration system in control station still needs

future development.

APPLICATIONS:

1. Home applications.2. Industrial applications.3. Power distributions.4. Laboratories.5. Consumer applications.

CONCLUSION:

The project “IMPLEMENTATION OF SMART SYSTEM BASED ON

SMART GRID SMART METER AND SMART APPLIANCES” has been

successfully designed and tested. Integrating features of all the hardware

components used have developed it. Presence of every module has been reasoned

out and placed carefully thus contributing to the best working of the unit.

Secondly, using highly advanced IC’s and with the help of growing technology

the project has been successfully implemented.

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FUTURE ASPECTS:

Most of the smart card systems in use today serve one purpose and are

related to just one process or is hardwired to only one application. A smart card

cannot justify its existence in this respect. The approach of future smart card is

therefore towards designing multi-application card with own operating system

based on open standard that can perform a variety of functions. It must be

configurable and programmable and it must be able to adapt to new situations and

new requirements especially in areas such as security, memory management, and

operating system. Most of smart card application methods today rely on the fact

that the code of functions to be performed should be imported by card operating

system from an outside server.

In the future, smart cards could handle multiple tasks for their owners, from

providing access to company networks, enabling electronic commerce, storing

health care information, providing ticket-less airline travel and car rentals, and

offering electronic identification for accessing government services such as

benefit payments and drivers licenses etc. Smart cards of the future may even stop

resembling "cards" as smart card technology is embedded into rings, watches,

badges, and other forms and factors that will make them remarkably convenient to

use. In the near future, we believe all PC’s and Network Computers will be

integrated with smart card readers.

REFERENCES:

[1] The 8051 Micro controller and Embedded Systems by -Muhammad Ali

Mazidi, Janice Gillispie Mazidi

[2] Electronic Components -D.V.Prasad

[3] Wireless Communications - Theodore S. Rappaport

[4] Power systems by C.L. Wadhwa

[5] Electrical Machines by J.B. Gupta

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[6] Syed Khizar Ali Zaidi, Hura Masroor , Syed Rehan Ashrafand Ahmed

Hassan , “Design and implementation of Low cost Electronic Prepaid energy

meter” Proceedings of the 12th IEEE International Multi topic Conference, pp.

542–552, , December 23-24,2008.

[7] N.LOCI, F.MOSSI AND M.TOSI “Virtual Instrument For Instantaneous

Power Measurement”,IEEE TRANS INSTRUM MEAS, VOL 41,NO 4,PP 528-

534 Aug 2002.

[8] The-8051:Micro-Controller, Architecture,Programming & Applications (2nd

edition) by KENNETH J. AYALA,Penaram International Pvt Ltd

[9] Paul Daigle “The Latest On Electronic Meters” Product Manager, Analog

Devices, Inc, masseachusetts.

[10] Rachel Kaplan, energy measurement ic’s simplify meter design –.

[11] Rajkamal, embedded systems architecture programming and design, 2nd

edition. tata mcgraw hill, 2008.

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