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Embedded Systems



 Applications of 

Embedded systems 

Submitted By:

Abhishek Vijayvargiya 2bv09ee003

Arjun Sanu 2bv09ee011

Jitesh Emmanuel 2bv09ee021Kanoj.B 2bv09ee022

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• About MODEM

• Architecture of MODEM

• What’s embedded in there? 

• Working

• Li-Fi- The future of Ultra Speed Data Transfer

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MODEM- MOdulator DEModulator

Is an electronic device that converts computer's digital information

into analog carrier signals and vice versa

 Modulation- is the process of changing the form of the signal

carrying the information.

 Demodulation- is process of extracting information from the

signals that are modulated.

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Different Types Of Modems

Modems are classified on the basis of different criteria such as the

place where they are installed, the manner in which they accept

information and the way they transmit signals. Based on these

criteria, modems are divided into the following types.

Internal and External Modems:

Internal modems are in the form of circuit boards, fitted in

expansion slots of the motherboard. An internal modem is a device

installed inside a desktop or laptop computer, allowing the

computer to communicate over a network with other connected

computers. There are two types of internal modems: dial-up and

WiFi® (wireless). Dial-up operates over a telephone line and

requires a network access phone number and logon credentials to

make a connection. WIFI connect wirelessly and without credentials

in certain cases.

External modems are enclosed in separate cases and not inside thesystem units. The modem is connected to the computer and telephone

line by means of two separate cables. Intelligent and Standard

Modems: Standard Modems: Most modems used today are called standard

modems. These modems are usually operated by commands entered from

a microcomputer keyboard. Users control the functions (dialing,

etc.) of a modem through the keyboard. Modems may use different

command languages to control their functions, but most modems

(called "Hayes compatible") use a popular language developed by a

company "Hayes Microcomputer Products, Inc." Intelligent Modems:Intelligent modems are also called advanced modems. These modems

can accept new instructions and then respond to the commands while

transmitting data and information. These can be done by

microprocessor chips and internal read only memory (ROM) contained

in the modem.Wireless and Short-Haul Modems: Short-Haul Modems:

Short- haul modems are devices that transmit signals down the cable

through any COM1 port. They sometimes are called modem eliminators,

because they do not require an external power source. They are also

called line drivers that can send data for a distance of more than

one mile. This type of modem can be used within or across several

buildings in a company or a university campus.Wireless Modems:

Wireless modems transmit the data signals through the air instead

of by using a cable. They sometimes are called a radiofrequency

modem. This type of modem is designed to work with cellular

technology, and wireless local area networks. Wireless modems are

not yet perfected, but the technology is rapidly improving.

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The Internal Architecture

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All the functions of modem are controlled and monitored by logic

control block. It has the following modules.

• Baud rate generator

•Clock generator

• Handshaking logic

• Tone detector

• Data compression & error detection

• Hayes command set

Baud rate generator: 

Baud rate is nothing but modulation rate. It is expressed in

terms of symbols per second or pulses per second. This

transmission/reception rate is determined by baud rate generator.

For example: bd1000=1000 pulse/sec.

Clock generator:

This circuit produces timing signals which helps in synchronizing the

circuit operation. It is usually a quartz piezoelectric oscillator &

may consist of resonant circuit & an amplifier.

Handshaking logic:

It is a hardware/software logic wherein signals are transmitted

back and forth over a communication network in order to maintain thevalid connection or synchronization. There are two types of

handshaking protocols and they are:-

• Simple handshaking protocol: Here the receiver sends message to


For eg.: The receiver may send message to sender saying ‚ I have

received our previous message & I’m ready for you to send me the

next message.‛ 

• Complex handshaking protocol: Here the sender may ask the receiver

or receiver may reply the sender.For eg.: The sender asks receiver if he is ready to receive or

receiver replies with ‚I did not receive your last message

correctly. Please send it again.‛ (if the data was corrupted in


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Tone detector:

Modem requires a channel which should be very clear. Therefore

it uses echo cancellation. But if the network is also performing the

echo cancellation, then the two cancellers end up in quarreling,

leading to bad results. Therefore to avoid this tone detector is used

which disables the echo cancellation of network.

Data compression & error detection:

Data compression enables information to be transmitted beyond

the actual connection speed. Data, particularly text & graphics

usually contain repeated sequence of identical information. Data

compression works by replacing many characters of repeated

information with few characters & transmitting only one copy of

repeated sequence of data.

While transferring data using modem, accidents can & do happen.

Because of noise the modem may misinterpret the signal receivedfrom other modem causing data corruption. To avoid this Microcosm

Network Protocol(MNP) is used.

Hayes command set:

It is a command language. It consists of series of short text

strings which combine together to produce complete commands for

operations like dialing & changing the parameters of the connection.

Most of the modem use this command set.

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Functions of MODEM

• Error Correction: Checks whether the data received is undamaged.


Divides the data into packets called frames.

Tags each packet with checksum to check redundancy.

Checks whether the data received is the same as sent.

Compressing data: The data is compressed & sent in bits over thenetwork. 

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What’s embedded in there ? 



Number Component

1 SOC µ processor

2 Pseudo-static RAM

3 Serial to Ethernet SOC

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1. SoC µprocessor

SoC with highly integrated display, media & imageprocessing.

• ARM® processor; 32-bit Reduced Instruction Set

Computer(RISC) instruction set architecture. Most of

the instructions are single machine cycle


• Integrated Ethernet Memory Access Control(MAC).

• USB 2.0 host for pc connectivity.

• Device ports to support 3G, WiFi®, Bluetooth® for

enhanced data connection.

• Integrated Stereo Class-D amplifier with speaker.

• 1080p Hardware Video engine for rich video quality.

2. PSRAM- Pseudo-Static RAM

• Similar to Static RAM.

• Combined features of DRAM & SRAM

• Inexpensive because of use of DRAM cell array

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3. Integrated Serial-to-Ethernet SoC

8051 CPU• 64KB ROM

• 32KB of SRAM

• 2 channel 8bit ADC

• 10/100Mbps Ethernet and UART

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When a modem first makes a connection, we hear screeching sounds

coming from the modem. These are digital signals coming from the

computer to which we are connecting being modulated into audible

sounds. The modem sends a higher-pitched tone to represent the digitI and a lower-pitched tone to represent the digit 0.

At the other end of the modem connection, the computer attached to

its modem reverses this process. The receiving modem demodulates the

various tones into digital signals and sends them to the receiving

computer. Actually, the process is a bit more complicated than

sending and receiving signals in one direction and then another.

Modems simultaneously send and receive signals in small chunks. The

modems can tell incoming from outgoing data signals by the type of

standard tones they use.

Another part of the translation process involves transmission

integrity. The modems exchange an added mathematical code along the

way. This special code, called a checksum, lets both computers know

if the data segments are coming through properly. If the mathematical

sums do not match, the modems communicate with each other by

resending the missing segments of data. Modems also have special

circuitry that allows them to compress digital signals before

modulating them and then decompressing them after demodulating the

signals. The compression/decompression process compacts the data so

that it can travel along telephone lines more efficiently.

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• 300 bps modem

Uses frequency shift keying (FSK)


Originating Modem : 0 for 1070 Hz tone

1 for 1270 Hz tone

Answering Modem : 0 for 2025 Hz tone

1 for 2225 Hz tone

Full-duplex operation

• 56K modem

Phase-shift keying(PSK)

Quadrature amplitude modulation (QAM)

• Asymmetric Digital Subscriber Line( ADSL)

Bandwidth Range from 24 KHz to 11 Mhz

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• Wi-Fi R & D in RTOS system has resulted in development of Wireless


Embedded Wi-Fi Modules with RTOS provide simple means of

wirelessly enabling any device

These modules communicate via internet

Since the data transfer happens wirelessly, the serial data

transfer bus is not present

The hardware required is complex as the clock signals are

required to be synchronized wirelessly

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 • Li-Fi

Large chunks of data are sent through light waves

Where a Wi-Fi gives data transfer rates of 10-100 Mbps, Li-

Fi supports data transfer upto 1 Gbps

The RTOS enabled embedded system has helped in unleashingwhat’s called as ‘what you see is what you send’ trend 


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• Wikipedia articles about modem

• www.howstuff 

• • http://www.avnet-