introduction

1. INTRODUCTION

Time division multiple access (TDMA) is a channel access method

for shared medium networks. It allows several users to share the same

frequency channel by dividing the signal into different time The users

transmit in rapid succession, one after the other, each using his own

time slot. This allows multiple stations to share the same transmission

medium (e.g. radio frequency channel) while using only a part of its

channel capacity slots.

Serial data communication is a popular means of transmitting data

between a computer and a peripheral device such as a programmable

instrument or even another computer. Serial communication uses a

transmitter to send data, one bit at a time, over a single

communication line to a receiver.

In our project currently through serial data connector RS232 we have

connected the PC to AT89C51 microcontroller based circuit which is

connected to two line 16 bit LCD. Serial communication is a form of

I/O in which the bits of a byte design transferred appear one after

another in a timed sequences on a single wire.

Using hyper link present in PC whatever data we typed on pc that is

shown on the LCD at the same time. In the extension of this project

instead of using two line 16 bit LCD we will use channel with TDMA

technique to connect more than one PC together and they can access

to the data using wireless communication network.

ADVANCED COMPUTER COMMUNICATION NETWORK USING TDMA

2. MULTIPLE ACCESS TECHNOLOGY

Different available multiple access technology are:

2.1 CDMA

Code division multiple access (CDMA) is a channel access method

used by various radio communication technologies. CDMA employs

spread-spectrum technology and a special coding scheme (where each

transmitter is assigned a code) to allow multiple users to be

multiplexed over the same physical channel. CDMA is a form of

spread-spectrum signaling, since the modulated coded signal has a

much higher data bandwidth than the data being communicated.

A spread spectrum technique spreads the bandwidth of the data

uniformly for the same transmitted power. Spreading code is a

pseudorandom code that has a narrow Ambiguity function, unlike

other narrow pulse codes. In CDMA a locally generated code runs at a

much higher rate than the data to be transmitted. Data for

transmission is simply logically XOR (exclusive OR) added with the

faster code. The figure shows how spread spectrum signal is

generated. The data signal with pulse duration of Tb is XOR added

with the code signal with pulse duration of Tc.


http://en.wikipedia.org/wiki/XOR

Each user in a CDMA system uses a different code to modulate their

signal. Choosing the codes used to modulate the signal is very

important in the performance of CDMA systems. The best

performance will occur when there is good separation between the

signal of a desired user and the signals of other users. The separation

of the signals is made by correlating the received signal with the

locally generated code of the desired user. If the signal matches the

desired user's code then the correlation function will be high and the

system can extract that signal. If the desired user's code has nothing in

common with the signal the correlation should be as close to zero as

possible (thus eliminating the signal); this is referred to as cross

correlation. If the code is correlated with the signal at any time offset

other than zero, the correlation should be as close to zero as possible.

This is referred to as auto-correlation and is used to reject multi-path

interference.


http://en.wikipedia.org/wiki/File:Generation_of_CDMA.svg

2.2 FDMA

Frequency Division Multiple Access or FDMA is a channel access

method used in multiple-access protocols as a channelization

protocol. FDMA gives users an individual allocation of one or several

frequency bands, allowing them to utilize the allocated radio spectrum

without interfering with each other. Multiple Access systems

coordinate access between multiple users.

Features

FDMA requires high-performing filters in the radio hardware, in

contrast to TDMA and CDMA.

FDMA is not vulnerable to timing problems as TDMA. Since a

predetermined frequency band is available for the entire period

of communication, stream data (a continuous flow of data that

may not be packetized) can easily be used with FDMA.

Due to the frequency filtering, FDMA is not sensitive to near-far

problem which is pronounced for CDMA.

Disadvantage: Crosstalk which causes interference on the other

frequency and may disrupt the transmission.


2.3 TDMA

Time division multiple access (TDMA) is a channel access method

for shared medium networks. It allows several users to share the same

frequency channel by dividing the signal into different time slots. The

users transmit in rapid succession, one after the other, each using his

own time slot. This allows multiple stations to share the same

transmission medium (e.g. radio frequency channel) while using only

a part of its channel capacity. High-speed local area networking over

existing home wiring (power lines, phone lines and coaxial cables) is

based on a TDMA scheme

TDMA characteristics

Shares single carrier frequency with multiple users

Non-continuous transmission makes handoff simpler

Slots can be assigned on demand in dynamic TDMA

Less stringent power control than CDMA due to reduced intra

cell interference

Higher synchronization overhead than CDMA

Advanced equalization may be necessary for high data rates if

the channel is "frequency selective" and creates Inter symbol

interference

Cell breathing (borrowing resources from adjacent cells) is more

complicated than in CDMA

Frequency/slot allocation complexity


3.COMMUNICATION CHANNEL

3.1 CHANNELIZATION

Channelization is a multiple access method in which the available

bandwidth of a link is shared in time, frequency, or through code

between different station. In telecommunications and computer

networks, a channel access method or multiple access method allows

several terminals connected to the same multi-point transmission

medium to transmit over it and to share its capacity. Examples of

shared physical media are wireless networks, bus networks, ring

networks, hub networks and half-duplex point-to-point links.

3.2 Frequency Division Multiple Access (FDMA)

In FDMA the available bandwidth is divided into frequency bands.

Each station is allocated to send it’s data. Each station is reserved for

a specific station and it belongs to the station all the time. The

frequency division multiple access (FDMA) channel-access scheme is

based on the frequency-division multiplex (FDM) scheme, which

provides different frequency bands to different data-streams. In the

FDMA case, the data streams are allocated to different users or nodes.

An example of FDMA systems were the first-generation (1G) cell-

phone systems. The FDM techniques combines the load from low

bandwidth channel and transmit them by using a high bandwidth

channel. The channel that are combined are low pass. The multiplexer

modulates the signals, combines them, and creates a band pass signal.

The bandwidth of the channel is shifted by the multiplexer.


While FDMA is an access method in the data link layer . The signal is

created in the allocated band .The signal created at each station are

automatically band pass filtered. They are mixed when they are sent

to common channel.

3.3 Time division multiple access (TDMA)

The time division multiple access (TDMA) channel access scheme is

based on the time division multiplex (TDM) scheme, which provides

different time-slots to different data-streams (in the TDMA case to

different transmitters) in a cyclically repetitive frame structure. For

example, user 1 may use time slot 1, user 2 time slot 2, etc. until the

last user. Then it starts all over again. In time division multiple

accesss the station share the bandwidth of the channel in time. Each

station is allocated a time slot during which it can send data. Each

station transmits its data in assigned time slot. TDMA & TDM

conceptually seems same but there is difference. TDM combines the

data from slower channel and transmits them by using a faster

channel. On the other hand TDMA is an access method in the datalink

layer. The datalink layer in each station tells its physical layer to use

the allocated time slot. There is no physical multiplexer at the

physical layer.

3.4 Code division multiple access (CDMA)

The code division multiple access (CDMA) scheme is based on

spread spectrum. An example is the 3G cell phone system. CDMA

differs from FDMA because only one channel occupies the entire


http://en.wikipedia.org/wiki/3G

http://en.wikipedia.org/wiki/Spread_spectrum

http://en.wikipedia.org/wiki/Code_division_multiple_access

http://en.wikipedia.org/wiki/Time_division_multiplex

http://en.wikipedia.org/wiki/Time_division_multiple_access

bandwidth of the link. It differs from TDMA because all stations can

send data simultaneously, there is no time sharing. CDMA simply

means communication with different codes. In CDMA through

common channel different codes are communicated simultaneously.

CDMA is based on coding theory. Each station is assigned a code,

which is a sequence of numbers called chip.

3.5 WIRED COMMUNICATION CHANNEL

3.5.1 Coaxial Copper Cable (COAX)

Coax consist of a single inner core conductor of solid copper wire

surrounded by three outer layers of material. The innermost layer is a

type of insulation, such as plastic , followed by a solid aluminum or

braided copper shield. A final jacket of PVC or Teflon protects the

conductor and prevents interference from outside signal.

Coax cable were once used in long distance telephone networks and

local area data network(LAN), but they are now primarily used for

cable TV installation. Coax utilizes frequency bandwidth of either 50-

350 Mhz to transmit analog tv signals.

3.5.2 OPTICAL FIBRE

An optical fiber is a thin, flexible, transparent fiber that acts as a

waveguide, or "light pipe", to transmit light between the two ends of

the fiber. Optical fibers are widely used in fiber-optic

communications, which permits transmission over longer distances

and at higher bandwidths (data rates) than other forms of

communication.


http://en.wikipedia.org/wiki/Bandwidth_(computing)

http://en.wikipedia.org/wiki/Fiber-optic_communication

http://en.wikipedia.org/wiki/Fiber-optic_communication

http://en.wikipedia.org/wiki/Waveguide_(optics)

Optical fiber typically consists of a transparent core surrounded by a

transparent cladding material with a lower index of refraction. Light is

kept in the core by total internal reflection. This causes the fiber to act

as a waveguide. Fibers which support many propagation paths or

transverse modes are called multi-mode fibers (MMF), while those

which can only support a single mode are called single-mode fibers

(SMF). Multi-mode fibers generally have a larger core diameter, and

are used for short-distance communication links and for applications

where high power must be transmitted. Single-mode fibers are used

for most communication links longer than 1,050 meters.

3.5.3 Applications

OPTICAL FIBER COMMUNICATION

Optical fiber can be used as a medium for telecommunication and

networking because it is flexible and can be bundled as cables. It is

especially advantageous for long-distance communications, because

light propagates through the fiber with little attenuation compared to

electrical cables. This allows long distances to be spanned with few

repeaters. For short distance applications, such as creating a network

within an office building, fiber-optic cabling can be used to save

space in cable ducts. This is because a single fiber can often carry

much more data than many electrical cables.

Fiber is also immune to electrical interference; there is no cross-talk

between signals in different cables and no pickup of environmental

noise.


http://en.wikipedia.org/wiki/Optical_communications_repeater

http://en.wikipedia.org/wiki/Computer_network

http://en.wikipedia.org/wiki/Single-mode_fiber

http://en.wikipedia.org/wiki/Multi-mode_fiber

http://en.wikipedia.org/wiki/Transverse_mode

http://en.wikipedia.org/wiki/Waveguide_(optics)

http://en.wikipedia.org/wiki/Total_internal_reflection

http://en.wikipedia.org/wiki/Index_of_refraction

http://en.wikipedia.org/wiki/Cladding

http://en.wikipedia.org/wiki/Core_(optical_fiber)

Other uses of optical fibers

Fibers are widely used in illumination applications. They are used as

light guides in medical and other applications where bright light needs

to be shone on a target without a clear line-of-sight path.

Optical fiber illumination is also used for decorative applications,

including signs, art, and artificial Christmas trees.

Optical fiber is also used in imaging optics. A coherent bundle of

fibers is used, sometimes along with lenses, for a long, thin imaging

device called an endoscope, which is used to view objects through a

small hole. Medical endoscopes are used for minimally invasive

exploratory or surgical procedures (endoscopy). Industrial endoscopes

are used for inspecting anything hard to reach.

3.5.4 Principle of Operation

An optical fiber is a cylindrical dielectric waveguide (nonconducting

waveguide) that transmits light along its axis, by the process of total

internal reflection. The fiber consists of a core surrounded by a

cladding layer, both of which are made of dielectric materials. To

confine the optical signal in the core, the refractive index of the core

must be greater than that of the cladding.


http://en.wikipedia.org/wiki/Endoscopy

http://en.wikipedia.org/wiki/Endoscope

http://en.wikipedia.org/wiki/Christmas_tree

http://en.wikipedia.org/wiki/Art

http://en.wikipedia.org/wiki/Commercial_signage

http://en.wikipedia.org/wiki/Light_tube

Index of refraction

The index of refraction is a way of measuring the speed of light in a

material. Light travels fastest in a vacuum, such as outer space. The

speed of light in a vacuum is about 300,000 kilometres (186 thousand

miles) per second. Index of refraction is calculated by dividing the

speed of light in a vacuum by the speed of light in some other

medium. The index of refraction of a vacuum is therefore 1 .

Total internal reflection

When light traveling in a dense medium hits a boundary at a steep

angle (larger than the "critical angle" for the boundary), the light will

be completely reflected. This effect is used in optical fibers to confine

light in the core. Light travels along the fiber bouncing back and forth

off of the boundary. Because the light must strike the boundary with

an angle greater than the critical angle, only light that enters the fiber

within a certain range of angles can travel down the fiber without

leaking out. This range of angles is called the acceptance cone of the


http://en.wikipedia.org/wiki/Acceptance_cone

http://en.wikipedia.org/wiki/Speed_of_light

http://en.wikipedia.org/wiki/Vacuum

http://en.wikipedia.org/wiki/Speed_of_light

fiber. The size of this acceptance cone is a function of the refractive

index difference between the fiber's core and cladding.

In simpler terms, there is a maximum angle from the fiber axis at

which light may enter the fiber so that it will propagate, or travel, in

the core of the fiber. The sine of this maximum angle is the numerical

aperture (NA) of the fiber. Fiber with a larger NA requires less

precision to splice and work with than fiber with a smaller NA.

Single-mode fiber has a small NA

Multi-mode fiber

Fiber with large core diameter (greater than 10 micrometers) may be

analyzed by geometrical optics. Such fiber is called multi-mode fiber,

from the electromagnetic analysis (see below). In a step-index multi-

mode fiber, rays of light are guided along the fiber core by total

internal reflection. Rays that meet the core-cladding boundary at a

high angle (measured relative to a line normal to the boundary),

greater than the critical angle for this boundary, are completely

reflected. The critical angle (minimum angle for total internal

reflection) is determined by the difference in index of refraction

between the core and cladding materials. In graded-index fiber, the

index of refraction in the core decreases continuously between the

axis and the cladding. This causes light rays to bend smoothly as they

approach the cladding, rather than reflecting abruptly from the core-

cladding boundary.


http://en.wikipedia.org/wiki/Critical_angle

http://en.wikipedia.org/wiki/Surface_normal

http://en.wikipedia.org/wiki/Ray_(optics)

http://en.wikipedia.org/wiki/Geometrical_optics

http://en.wikipedia.org/wiki/Numerical_aperture

http://en.wikipedia.org/wiki/Numerical_aperture

http://en.wikipedia.org/wiki/Sine

Single-mode fiber

As an optical waveguide, the fiber supports one or more confined

transverse modes by which light can propagate along the fiber. Fiber

supporting only one mode is called single-mode or mono-mode fiber.

The most common type of single-mode fiber has a core diameter of

8–10 micrometers and is designed for use in the near infrared. The

mode structure depends on the wavelength of the light used, so that

this fiber actually supports a small number of additional modes at

visible wavelengths.

3.5.5 OPTICAL FIBER CABLES

In practical fibers, the cladding is usually coated with a tough resin

buffer layer, which may be further surrounded by a jacket layer,

usually glass. These layers add strength to the fiber but do not

contribute to its optical wave guide properties. Rigid fiber assemblies

sometimes put light-absorbing ("dark") glass between the fibers, to

prevent light that leaks out of one fiber from entering another. This

reduces cross-talk between the fibers, or reduces flare in fiber bundle

imaging applications. Another important feature of cable is cable

withstanding against the horizontally applied force. It is technically

called max tensile strength defining how much force can applied to

the cable during the installation period.


http://en.wikipedia.org/wiki/Lens_flare

http://en.wikipedia.org/wiki/Crosstalk_(electronics)

http://en.wikipedia.org/wiki/Buffer_(optical_fiber)

http://en.wikipedia.org/wiki/Resin

http://en.wikipedia.org/wiki/Near_infrared

http://en.wikipedia.org/wiki/Transverse_mode

3.5.6 TERMINATION AND SPLICING

Optical fibers may be connected to each other by connectors or by

splicing, that is, joining two fibers together to form a continuous

optical waveguide. The generally accepted splicing method is arc

fusion splicing, which melts the fiber ends together with an electric

arc. For quicker fastening jobs, a "mechanical splice" is used.

Fusion splicing is done with a specialized instrument that typically

operates as follows: The two cable ends are fastened inside a splice

enclosure that will protect the splices, and the fiber ends are stripped

of their protective polymer coating (as well as the more sturdy outer

jacket, if present). The ends are cleaved (cut) with a precision cleaver

to make them perpendicular, and are placed into special holders in the

splicer. The splice is usually inspected via a magnified viewing screen

to check the cleaves before and after the splice. The splicer uses small

motors to align the end faces together, and emits a small spark

between electrodes at the gap to burn off dust and moisture. Then the

splicer generates a larger spark that raises the temperature above the

melting point of the glass, fusing the ends together permanently.

Mechanical fiber splices are designed to be quicker and easier to

install, but there is still the need for stripping, careful cleaning and

precision cleaving. The fiber ends are aligned and held together by a

precision-made sleeve, often using a clear index-matching gel that

enhances the transmission of light across the joint. Such joints

typically have higher optical loss and are less robust than fusion


http://en.wikipedia.org/wiki/Index-matching_gel

http://en.wikipedia.org/wiki/Melting_point

http://en.wikipedia.org/wiki/Electric_arc

http://en.wikipedia.org/wiki/Electric_arc

http://en.wikipedia.org/wiki/Fusion_splicing

http://en.wikipedia.org/wiki/Fusion_splicing

splices, especially if the gel is used. All splicing techniques involve

the use of an enclosure into which the splice is placed for protection

afterward.

3.6 WIRELESS COMMUNICATION

Wireless communication is the transfer of information without the use

of wires. The distances involved may be short (a few meters as in

television remote control) or long (thousands or millions of kilometers

for radio communications). The term is often shortened to "wireless".

It encompasses various types of fixed, mobile, and portable two-way

radios, cellular telephones, personal digital assistants (PDAs), and

wireless networking.

Wireless operations permits services, such as long range

communications, that are impossible or impractical to implement with

the use of wires. The term is commonly used in the

telecommunications industry to refer to telecommunications systems

(e.g. radio transmitters and receivers, remote controls, computer

networks, network terminals, etc.) which use some form of energy

(e.g. radio frequency (RF), infrared light, laser light, visible light,

acoustic energy, etc.) to transfer information without the use of wires.

Information is transferred in this manner over both short and long

distances.


http://en.wikipedia.org/wiki/Wireless_network

http://en.wikipedia.org/wiki/Personal_digital_assistant

http://en.wikipedia.org/wiki/Mobile_phone

http://en.wikipedia.org/wiki/Two-way_radio

http://en.wikipedia.org/wiki/Two-way_radio

3.6.1 WIRELESS NETWORKS

Wireless networking (i.e. the various types of unlicensed 2.4 GHz

WiFi devices) is used to meet many needs. Perhaps the most common

use is to connect laptop users who travel from location to location.

Another common use is for mobile networks that connect via satellite.

A wireless transmission method is a logical choice to network a LAN

segment that must frequently change locations. The following

situations justify the use of wireless technology:

To span a distance beyond the capabilities of typical cabling,

To provide a backup communications link in case of normal

network failure,

To link portable or temporary workstations,

To overcome situations where normal cabling is difficult or

financially impractical, or

To remotely connect mobile users or networks

3.6.2 APPLICATIONS OF WIRELESS TECHNOLOGY

Security systems

Wireless technology may supplement or replace hard wired

implementations in security systems for homes or office buildings.

Television remote control

Modern televisions use wireless (generally infrared) remote control

units. Now radio waves are also used.


Cellular telephone (phones and modems)

The best known example of wireless technology is the cellular

telephone and modems. These instruments use radio waves to enable

the operator to make phone calls from many locations worldwide.

They can be used anywhere that there is a cellular telephone site to

house the equipment that is required to transmit and receive the signal

that is used to transfer both voice and data to and from these

instruments.

Wi-Fi

Wi-Fi is a wireless local area network that enables portable

computing devices to connect easily to the Internet. Standardized as

IEEE 802.11 a,b,g,n, Wi-Fi approaches speeds of some types of wired

Ethernet. Wi-Fi hot spots have been popular over the past few years.

Some businesses charge customers a monthly fee for service, while

others have begun offering it for free in an effort to increase the sales

of their goods.

Wireless energy transfer

Wireless energy transfer is a process whereby electrical energy is

transmitted from a power source to an electrical load that does not

have a built-in power source, without the use of interconnecting

wires.


http://en.wikipedia.org/wiki/Ethernet

http://en.wikipedia.org/wiki/IEEE_802.11

http://en.wikipedia.org/wiki/Internet

http://en.wikipedia.org/wiki/Local_area_network

http://en.wikipedia.org/wiki/Wireless_modem

http://en.wikipedia.org/wiki/Cellular_telephone

http://en.wikipedia.org/wiki/Cellular_telephone

Computer interface devices

Answering the call of customers frustrated with cord clutter, many

manufactures of computer peripherals turned to wireless technology

to satisfy their consumer base. Originally these units used bulky,

highly limited transceivers to mediate between a computer and a

keyboard and mouse, however more recent generations have used

small, high quality devices, some even incorporating Bluetooth. These

systems have become so ubiquitous that some users have begun

complaining about a lack of wired peripherals. Wireless devices tend

to have a slightly slower response time than their wired counterparts,

however the gap is decreasing. Initial concerns about the security of

wireless keyboards have also been addressed with the maturation of

the technology.


http://en.wikipedia.org/wiki/Bluetooth

4.BLOCK DIAGRAM


RECTIFIER CIRCUIT


5. WORKING PRINCIPLE

12v AC is given to I/P of bridge rectifier ,it uses 4 diode and has no

centre tap transformer. The O/P of the bridge rectifier is pulsating

DC, so to reduce the pulsating nature of the O/P we are using 1000µf

capacitor(smoothing capacitor).Then this 12v is fed to the 7805

voltage regulator and we get constant 5v DC. This 5v DC acts as

VCC to the AT89C51 at pin 40.Crystal oscillator circuit is connected

to pin-18 and 19 to give stable oscillator frequency and here we are

using 2 capacitor(33pf) to reduce noise. The negative end of

capacitor(22µf ) is connected to the pin no.9 of the AT89C51 to reset it

,during the startup time. MAX 232 is interface to the AT89C51 to

convert the CMOS level to the TTL level and vice-versa. Pin 11 of

MAX232 is connected to pin-11 of AT89C51 & pin-12 of MAX232

is connected to pin-10 of AT89C51 and pin-14 is connected to pin-2

of DB9 and pin-13 is connected to pin-3 of DB9.


6.COMPONENTS

6.1 INTRODUCTION TO AT89C51:

FEATURES:

8-bit microcontroller with 4K bytes of In-system reprogrammable

Flash memory

Fully Static Operation: 0 Hz to 24 MHz

Three-Level Program Memory Lock

128 x 8-Bit Internal RAM

32 Programmable I/O ports

Two 16-Bit Timer/Counters

Six Interrupt Sources

1 Serial port

Low Power Idle and Power Down Modes

6.2 DESCRIPTION

The AT89C51 is a low-power, high performance CMOS 8-bit

microcomputer with 4Kbytes of Flash Programmable and Erasable

Read Only Memory (PEROM).. The on-chip Flash allows the

program memory to be reprogrammed in-system or by a

conventional nonvolatile memory programmer. By combining a

versatile 8-bit CPU with Flash on a monolithic chip, the Atmel

AT89C51 is a powerful microcomputer which provides a highly

flexible and cost effective solution to many embedded control

applications.


6.3 PACKAGES OF AT89C51

The AT89C51 family members come in different packages:

44A

PACKAGE TYPE

44 lead, Thin Plastic Gull Wing Quad

Flat Pack (TQFP)

44 lead, Plastic J-Leaded Chip

Carrier (PLCC)

40 lead,0.600* wide, Plastic Dual

Inline Package (PDIP)

44 lead, Plastic Gull Wing Quad Flat

pack (PQFP)

44J

40P6

44Q

6.4 PIN CONFIGURATION


AT89C51

PIN DISCRIPTION

AT89C51 chip contains 40 pins. These are described below:

VCC:

Pin 40 provides supply voltage to the chip. The voltage source is

+5V

GND

Pin 20 is connected to Ground.

PORT 0 (PIN 32-39)

Port 0 is an 8-bit open drain bi-directional I/O port. As an

output port each pin can sink eight TTL inputs. When 1s

are written to port 0 pins, the pins can be used as high

impedance inputs.

This port can be used for input or output. Each pin of these

pins must be connected externally to pull up resistor.

PORT 1(PIN 01-08)

Port 1 is an 8-bit bidirectional 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.

PORT2(pin 21-28)

Port 2 is an 8-bit bidirectional 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.

.


PORT3(pin10-17)

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 used as inputs.

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

AT89C51 as listed below:

Port Pin Alternate Functions

P3.0 RXD (serial input port) P3.1 TXD (serial output port) P3.2 INT0(external interrupt0) P3.3 INT1(external interrupt1) P3.4 T0(timer0 external input) P3.5 T1(timer1 external input) P3.6 WR(external data memory write

strobe) P3.7

RD(external data memory read strobe)

P3.0 &P3.1 are used for the RxD & TxD serial

communication signals.

RST


The reset input on pin 9 is used to reset the microcontroller. A

high pulse to this pin, microcontroller will resets & terminate all

activities.

ALE/PROG

Address Latch Enable signals on pin 30 is used for demultiplexing

the address &data bus.

PSEN (PROGRAM STORE ENABLE):

This connected to pin no 29.

It is the read strobe to external program Memory.

EA/VPP

This signal is connected to pin no-31.

It is called as ‘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.

EA should be strapped to VCC for internal program

executions.

XTAL1 This signal is connected to pin 19.

Input to the inverting oscillator amplifier and input to the

Internal clock operating circuit.

XTAL2

This signal is connected to pin 18.

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.

Most often a quartz crystal oscillator connected to XTAL1

and XTAL2 needs two capacitors each of 33pF value .One

side of capacitors is connected to ground.

The oscillator connections are shown in the following

figure

XTAL connections to an External Clock Source are shown in the

figure


The reset pin (pin 9) is often referred to as power-on reset.

Activating a power-on reset will cause all values in the registers

to be lost.

IDLE MODE

In idle mode, the CPU puts itself to sleep while all the on chip

peripherals remain active. The mode is invoked by software.

The content of the on-chip RAM and all the special functions

registers remain unchanged during this mode.

The idle mode can be terminated by any enabled interrupt or by

a hardware reset.

POWER DOWN MODE

In the power down mode the oscillator is stopped, and the

instruction that invokes power down is the last instruction

executed. The on-chip RAM and Special Function Register

retain their values until the power down mode is terminated.


The power-on reset circuit is shown below:

6.5 BLOCK DIAGRAM


6.6 BLOCK DESCRIPTION


REGISTERS

In a CPU, register are used to store information temporarily.

The most widely used 8-bit registers of AT89C51 are:

ACCUMULATOR-

It is used in arithmetic & logic well as in, (I/O) instruction.

B REGISTER-

REGISTER BANK (BANK0-BANK3)-

32 bytes locations of internal memory contains the register banks.

This is divided into 4 banks of register and in each bank there are 8

registers like R0-R7.


The most widely used 16-bit registers of AT89C51:

DPTR REGISTER-

It is 16-bit, it can also be accessed as two 8-bit register, DPH

&DPL, where DPH is the high byte and DPL is the low byte.

PROGRAM COUNTER(PC)-

It is the 16-bit wide register which points to the address of the

next instruction to be executed.

PSW(PROGRAM STATUS WORD) REGISTER-

This register is an 8-bit register. It is referred to as flag

register. Only 6 bits of it are used by AT89C51.The two

unused bits are user-defined flags. Four of the flags are called as

conditional flags. These are: CY(carry), AC(auxiliary carry ),

P(parity), &O(overflow).

The bits of PSW Register are shown below:

CY AC F0 RS1 RS0 OV -- P

RS1, RS0 are used to change the bank registers.

F0 - available to the user for general purpose.

-- User definable bit

STACK POINTER


Stack pointer register is a 16-bit wide is decremented

automatically when each data is pushed onto the stack and is

incremented automatically when data is popped off the stack.

INSTRUCTION REGISTER

When an instruction is fetched from memory, it is loaded in

instruction register.

ALU(Arithmetic & Logic unit):

This unit performs the necessary arithmetic/logical calculations.

There are 4 port drivers:

Port 0 Drivers(Port 0.0 - Port 0.7)




RAM MEMORY SPACE ALLOCATION

There are 128 bytes of RAM in the AT89C51. These are

assigned addresses 00 to 7FH.

These 128 bytes are divided into 3 different groups:

A total of 32 bytes from location 00 to 1FH are set aside for

register bank and the stack.

A total of 16 bytes from locations 20H to 2FH are set aside for

bit addressable read/write memory.

A total of 80 bytes from locations 30H to 7FH are used for

storage, and is called as scratch pad. These 80 locations of RAM

are widely used for the purpose of storing data.


PORT LATCH

In reading a port ,some instructions read the status of port pins while

other read the status of an internal port latch.

There are 4 port latch: Port 0 latch, Port 1latch ,Port 2 latch, Port 3

latch

TIMING &CONTROL

This unit generates the clock signals and control signals for

communication between the microcontroller & peripherals.

These signals are:

PSEN

ALE/ PROG

EA/ Vpp

RST


FLASH

To use the AT89C51 develop a microcontroller based system

requires a ROM burner that support Flash memory; however

unlike 8051 ,here a ROM eraser is not needed.

In flash memory , we must erase the entire contents of ROM in

order to program it again.

This erasing of flash is done by the PROM burner itself and that

is why separate eraser is not needed

TIMER PROGRAMMING IN AT89C51:

Basic registers of the timer-

Timer 0 register:

The 16-bit register of timer 0 is accessed as low byte and high

byte. The low byte register is called TL0 (timer0 low byte) and

the high byte register is referred to as TH0(timer0 high byte).

The timer0 registers are shown below:

D15 D1

4

D13 D1

2

D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

TH0 TL0

Timer1 register:

Timer1 is also 16 bits, and is split into two bytes, referred to as

TL1(timer1 low byte) and TH1(timer1 high byte).

Timer1 register are shown below :


D15 D1

4

D13 D1

2

D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

TH1 TL1

TMOD (timer mode) register:

Both timers0 and 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 are set aside for timer1.

The TMOD registers are shown below:

GATE C/T M1 M0 GATE C/T MI M0

TIMER 1 TIMER 0

GATE- When gate is set , it will use external method to start &

stop the timer. Timer/counter is enabled only while the INTX

pin is high and the TRX control pin is set. When cleared the

timer is enabled whenever the TRX control bit is set.

C/T- This bit in the TMOD register is used to decide whether

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

is used as delay generator

M1,M0- M0 and M1 select the timer mode. There are 3

modes:0,1,2,3.

Modes are described below:

M1 M0 MODE OPERATING

MODE

0 0 0 13-bit timer mode

(5-bit prescaler).


(MSB) (LSB)

0 1 1 16-bit timer

mode( no prescaler).

1 0 2 8-bit auto reload

C/T, THX hold a

value which is to be

reloaded into TLX

each time it

overflows.

1 1 3 Split timer mode.

- For maximum delay, mode 1 is used because it counts up to FFFF.

- For serial communication, mode 2 is used. Here, after THX is loaded

with the 8- bit value, it is automatically reloaded to TLX.

Timer flag (TFX)-

It is the flag which is set when timer overflows.

It is manually cleared for next operation.

It is set by the hardware & cleared by the

software.

Timer start (TRX)-

This is used to start / stop the timers

It is set to start.

It is clear to stop.

It is set & cleared by software.

TCON REGISTER

TF TR1 TF0 TR0 IE1 IT1 IE0 IT0


1

It is a bit- addressable 8 bit SFR(special function register) present

in the AT89C51 to control the timer. The upper four bits are used to

store the TF and TR bits of both timer0 and timer1.The lower 4 bits

are set aside for controlling the interrupt bits .

CLOCK SOURCE FOR TIMER

Every timer needs a clock pulse to tick. If C/T=0,the crystal frequency

attached to the AT89C51 is the source of the clock for the timer. this

means that the size of the crystal frequency attached to the

microcontroller decides the speed at which the AT89C51 timer ticks.

The frequency for the timer is always 1/12th the frequency of the

crystal oscillator.

XTAL frequency has the range between 10 MHZ to 40 MHZ, we will

concentrate on the XTAL frequency of 11.0592 MHZ for serial

communication.

6.7 MAX 232

FEATURES:

Operates From a Single 5-V Power Supply With 1.0-_F Charge-

Pump Capacitors

Operates Up To 120 kbit/s

Two Drivers and Two Receivers

±30-V Input Levels


Low Supply Current . . . 8 mA Typical

APPLICATIONS:

TIA/EIA-232-F, Battery-Powered Systems, Terminals,

Modems, Computers.

PIN CONFIGURATION OF MAX232


DESCRIPTION

Since the RS232 is not compatible with todays micro processor & micro

controller, we need a line driver ( voltage converter) to convert RS232’s

signals to TTL voltage levels that will be acceptable to the AT89C51

TxD & RxD pins.

MAX232 is an integrated circuit that converts signals from RS232 serial

to signal suitable for using TTL compatible digital logic circuits.i.e it

converts from RS232 voltage levels to TTL voltage levels and viceversa.

The MAX232 is a dual driver/receiver that includes a capacitive voltage

generator to supply TIA/EIA-232-F voltage levels from a single 5-V

supply and converts RX, TX, CTS & RTS signals .

Advantages: MAX232 uses a +5V power source which is same as the

source voltage for AT89C51.

It has two sets of line drivers for transferring and receiving data.The line

drivers used for TxD are called T1 & T2, while the line drivers for RxD

are R1& R2 respectively.

MAX232 requires 4 capacitors ranging from 1 to 22µF, but the most

widely used is 22 µF.

In many applications only one of each is used i.e T1 & R1 are used

together for TxD & RxD of AT89C51 and the second set is left unused.


6.8 VOLTAGE REGULATORS

The 78xx (also sometimes known as LM78xx) series of devices is a

family of self-contained fixed linear voltage regulator integrated

circuits. When specifying individual ICs within this family, the xx is

replaced with a two-digit number, which indicates the output voltage

the particular device is designed to provide (for example, the 7805 has

a 5 volt output, while the 7812 produces 12 volts).

The 78xx line are positive voltage regulators, meaning that they are

designed to produce a constant voltage that is positive relative to a

common ground. 78xx ICs have three terminals

7805 VOLTAGE REGULATORS:

The 7805 provides circuit designers with an easy way to regulate DC

voltages to 5v.


http://en.wikipedia.org/wiki/Voltage

http://en.wikipedia.org/wiki/Integrated_circuits

http://en.wikipedia.org/wiki/Integrated_circuits

http://en.wikipedia.org/wiki/Linear_regulator

Encapsulated in a single chip/package (IC), the 7805 is a positive

voltage DC regulator that has only 3 terminals. They are: Input

voltage, Ground, Output Voltage.

Although the 7805 were primarily designed for a fixed-voltage output

(5V), it is indeed possible to use external components in order to

obtain DC output voltages of: 5V, 6V, 8V, 9V, 10V, 12V, 15V, 18V,

20V, 24V. It should be noted that the input voltage must, of course, be

greater that the required output voltage, so that it can be regulated

downwards.

GENERAL FEATURES:

Output Current up to 1A

Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

Thermal Overload Protection

Short Circuit Protection

Output Transistor Safe Operating Area Protection

DIAGRAMATIC REPRESENTATION


7812 VOLTAGE REGULATORS:

The H7812 series of three terminal positive Regulators are available

in the TO-220 package and with several fixed output voltages, making


them useful in a wide range of applications. Each type employs

internal current limiting, Thermal shut down and safe operating area

protection, making it essentially indestructible. If adequate heat

sinking is provided, they can deliver over 1A output current.

GENERAL FEATURES

Output current up to 1A

Output Voltages of 12V

Thermal Overload Protection

Short Circuit Protection

Output Transistor Safe Operating Area Protection

DIAGRAMATIC REPRESENTATION

ADVANTAGES

Th

e se

ICs

do

not

require any additional components to

provide a constant, regulated source of power.

These series ICs have built-in protection against a circuit

drawing too much power. They also have protection against


overheating and short-circuits, making them quite robust in most

applications. In some cases, the current-limiting features of the

78xx devices can provide protection not only for the 78xx itself,

but also for other parts of the circuit it is used in, preventing

other components from being damaged as well.

6.9 LCD

A liquid crystal display (LCD) is a thin, flat electronic visual display

that uses the light modulating properties of liquid crystals (LCs). LCs

do not emit light directly.

16 CHARECTER X 2 LINE LCD:

Description

This is the first interfacing example for the Parallel Port. We will start

with something simple. This example doesn't use the Bi-directional

feature found on newer ports, thus it should work with most, if no all

Parallel Ports. It however doesn't show the use of the Status Port as an

input. So what are we interfacing? A 16 Character x 2 Line LCD

Module to the Parallel Port. These LCD Modules are very common

these days, and are quite simple to work with, as all the logic required

to run them is on board.

Schematic


http://en.wikipedia.org/wiki/Liquid_Crystals

http://en.wikipedia.org/wiki/Electronic_visual_display

Circuit Description:

Above is the quite simple schematic. The LCD panel's Enable and

Register Select is connected to the Control Port. The Control Port is

an open collector / open drain output. While most Parallel Ports have

internal pull-up resistors, there are a few which don't. Therefore by

incorporating the two 10K external pull up resistors, the circuit is

more portable for a wider range of computers, some of which may

have no internal pull up resistors.

We make no effort to place the Data bus into reverse direction.

Therefore we hard wire the R/W line of the LCD panel, into write

mode. This will cause no bus conflicts on the data lines. As a result

we cannot read back the LCD's internal Busy Flag which tells us if the


LCD has accepted and finished processing the last instruction. This

problem is overcome by inserting known delays into our program.

The 10k Potentiometer controls the contrast of the LCD panel.

Nothing fancy here. As with all the examples, I've left the power

supply out. You can use a bench power supply set to 5v or use a

onboard +5 regulator. Remember a few de-coupling capacitors,

especially if you have trouble with the circuit working properly.

The 2 line x 16 character LCD modules are available from a wide

range of manufacturers and should all be compatible with the

HD44780. The one I used to test this circuit was a Powertip PC-

1602F and an old Philips LTN211F-10 which was extracted from a

Poker Machine! The diagram to the right, shows the pin numbers for

these devices. When viewed from the front, the left pin is pin 14 and

the right pin is PIN1

7.BASICS OF SERIAL COMUNICATION

Computer transfer the data in two ways: parallel and serial.

In case of parallel data transfer ,often 8 or more lines (wire

conductors) are used to transfer data to a hard disk ;each uses


cables with many wire strips.eg-parallel transfers are printers and

hard disks; each uses cables many wire strips. Here one byte or

more than that data sent at a time.

In case of serial communication ,data is sent one bit at a time .

So that serial communication is used for transferring data

between two system located at distances of hundred millions

miles apart like an telephonic system .shown in the diagram-

DIAGRAM

For serial data communication to work ,the byte of data must be

converted to serial bits using a parallel-in-serial–out(PISO)shift

register,then it can be transmitted over a single data line.

The data transferred in telephone line the data must be

converted from 0s and 1s to audio tones,which are sinusoidal–

shaped signals .

This conversion is performed by a peripheral device called as

MODEM, which is known as modulator/demodulator.


When the distance is short , the digital signal can be transferred

as it on a simple wire and requires no modulation.This is how

IBM PC key boards transfer data to the motherboard.

Serial data communication requires two methods :-

1-Synchronous method.

2-Asynchronous method.

In case of a a synchronous method transfer a block of data

(character ) at a time.

In case of Asynchronous method transfer a single byte at a time.

RS-232

It is a is a interface that a computer uses to talk and exchange data

with a modem and other serial devices.

An RS-232 port can supply only limited power to another device. The

number of output lines, the type of interface driver IC, and the state of

the output lines are important considerations.

The types of driver ICs used in serial ports can be divided into

three general categories:

Drivers which require plus (+) and minus (-) voltage power

supplies such as the 1488 series of interface integrated circuits.

(Most desktop and tower PCs use this type of driver.)

Low power drivers which require one +5 volt power supply.

This type of driver has an internal charge pump for voltage


conversion. (Many industrial microprocessor controls use this

type of driver.)

Low voltage (3.3 v) and low power drivers which meet the EIA-

562 Standard. (Used on notebooks and laptops.) .

RS232 ON DB9(9-PIN D-TYPE CONNECTOR)

Figure of male DB-9 port

Figure of female DB-9 port

PCB DESIGN SECTION

A PCB is a thing that we will require when we are deciding our

project. A proper PCB ensure that various circuit are interconnected

as per circuit diagram.

8.PCB FABRICATION

IC’S USED- AT89C51 Microcontroller , MAX232

Resistors (10k),

Capacitors (33pf ,22µf,10µF),

Crystal oscillator (11.0592 MHz),


Diodes(IN 4007),

7805 Voltage regulators,

RS-232 DB-9 Connector

9.PROGRAM USED

PROGRAM FOR LCD:

#include "lcd.h"


void lcd_init(){ lcd_cmd(0x38); //2 lines 5x7 matrix lcd_cmd(0x0C); //Display on cursor off lcd_cmd(0x06); //Increment cursor shift cursor to right lcd_cmd(0x01); //Clear screen}

void lcd_cmd(unsigned char cdata){ lcd_ready(); ldata = cdata; rs = 0; rw = 0; en = 1; delay(1); en = 0; return;}

void lcd_data(unsigned char avalue){ lcd_ready(); ldata = avalue; rs = 1; rw = 0; en = 1; delay(1); en = 0; return;}

void delay(unsigned int time){ unsigned int i,j; for(i = 0;i<time;i++) for(j=0;j<1275;j++);}

void lcd_ready(){ busy = 1; rs = 0;


rw = 1; while(busy == 1) { en = 0; delay(1); en = 1; } return;}

void lcd_num(unsigned int x) { unsigned char d[6]; char i=0;

if(x == 0) { lcd_data(48); return; } while(x != 0) {

d[i]= (x % 10);i++;x=(x/10);

} while(i!= 0) { lcd_data(d[--i]+48); } }

void lcd_string(unsigned char *str) { while(*str)

lcd_data(*str++); }

PROGRAM OF LCD HEADER FILE(LCD.H):

#include <REGX51.H>

#ifndef __LCD_H__


#define __LCD_H__

void lcd_init( );void lcd_cmd(unsigned char );void lcd_data(unsigned char );void lcd_string(unsigned char []);void lcd_num(unsigned int );void lcd_ready( );void delay(unsigned int );

sfr ldata = 0xA0;sbit rs = P3^7;sbit rw = P3^6;sbit en = P3^5;sbit busy = P2^7;

#endif

PROGRAM OF UART HEADER FILE(UART.H):

#ifndef __UART_H__#define __UART_H__

void serial_init(unsigned char ); //Initialise serial communicationvoid serial_tx(unsigned char ); //Transmit a character on serial portunsigned char serial_rx( ); //Recieve a character on serial portvoid string_tx(unsigned char[] ); //Transmit a string on serial portvoid num_tx(unsigned int ); //Transmit a number on serial port

#endif

PROGRAM FOR SERIAL TEST:

# include<lcd.h># include<uart.h>

void main(){


unsigned char r,i; lcd_init(); serial_init(0xFD); lcd_string("SERIAL TEST"); string_tx("SERIAL TEST \n"); delay(100); lcd_cmd(0x01); //Clear the screen while(1) { lcd_cmd(0x80); //Cursor to first line for(i=0;i<16;i++) { r = serial_rx(); serial_tx(r); lcd_data(r); } lcd_cmd(0xC0); //Cursor to second line for(i=0;i<16;i++) { r = serial_rx(); serial_tx(r); lcd_data(r); } lcd_cmd(0x01); //Clear the screen }}

10. CONCLUSION

Currently we have designed an AT89C51 micro-controller based

circuit which is connected through PC by RS232 serial

communication connector. The microcontroller is also connected to


LCD and through hyper link terminal whatever we type on PC that

will be display on 16 bit two line LCD.

In the extension of this project instead of using two line 16 bit LCD

we will use channel with TDMA technique to connect more than one

PC together and they can access to the data using wireless

communication network.


introduction

Documents

data signal

code signal

multiple users

serial data communication

multiple access systems

channel access methodfor

multipleaccess protocols

radio frequency channel