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Data Communication Explained

Data communication is fundamentally a simple operation. Point

A sends information to Point B and Point B receives it. A slightly

more complex, and more practical, system allows Point A to send

information to and receive information from Point B, and vice

versa. It is what lies between points A and B that has been the

substance of data communication system development since

before the personal computer, or any computer for that matter,

was ever invented.

For example, consider several simple examples of data

communication systems that have nothing to do with computers:

Paul Revere used a very basic system, whereby one light in the

tower signified the British were approaching by land, and two

indicated they were approaching by sea. During a game of blind-

man's-bluff, the subject hears a sound when he comes within a

certain distance of an object, and nothing when he is out of

range. To solve the problem of knowing when dishes in a

dishwasher are clean or dirty, a family might decide to place a

black magnet on the dishwasher when dirty dishes are put in,

and then change it to a white magnet when the cleaning cycle is

started, and return the black magnet after it is emptied. The one

thing all these examples have in common is that they all use

two-state systems of communication. A two-state system is one

which uses only two possible values to transmit information--

the lamp is on or it is off, there is a sound or there is silence, the

magnet is black or white, etc. The way these values are combined

allows complex messages to be transmitted using very simple

tools.

Consider Morse Code, a two-state data communication system

that functions very similarly to today's computerized data

communication systems. Developed by Samuel E.B. Morse in

the 19th century, Morse code uses electrical current to transmit

a series of dashes and dots that represent letters of the alphabet,

numbers, a comma and a period. A basic Morse Code transaction

works as follows: A "message" is given to an operator who

translates that message into dots and dashes (Point A), then the

transmitting operator uses the telegraph key to send an electrical

signal to the receiving operator at the desired location to indicate

that a message is about to come through. The receiving operator

(point B) sends back an acknowledgment that he is ready, and

the transmitting operator then sends the message which the

receiving operator takes down. When the message is completely

transmitted, the transmitting operator signals to the receiving

operator that he is done, and the transmission line is closed. The

receiving operator then translates the code back into the original

message, and delivers it to the designated recipient.

Clearly, in a system of this type, accuracy is extremely important.

As only two characters--dot or dash--are used to create a code

for an entire language system, the transmitting and receiving

operators must be extremely accurate. (Indeed, it makes a big

difference whether the message says "Give one million dollars to

Ted" or "Give one million dollars to Ned"--an easy mistake to

make using Morse code, as the letter T is "-" and the letter N is

"-.") This system can only work if both sides of the data

communication system know the code and can encrypt and

decode messages. It is also essential that the transmitter not

send faster than the receiver can take-down the information.

Even using expert operators, static on the line could obscure

the signals making a dash sound like a dot and thereby corrupting

the message. Thus, it becomes obvious that the most important

aspect of designing a data communication system is ensuring

not only that Point B can receive and understand the data

transmitted by Point A, but also that the data remain uncorrupted

during transmission.

These are the very same concerns faced by computerized data

communication system designers. Indeed Morse code is often

though of as the forerunner of the computer's binary

communication system. The binary system uses the numbers 0

and 1 as the symbols for transmission of data. Using positional

notation, any value is represented by a weighted series of 1s

and 0s. Thus the decimal number "33" would be represented

by "100001" (1 x 2

+ 0 x 2

+ 1 x 2

The above is a simple example of binary coding, but the same

system is used by computers to transmit complex text messages,

complex graphics, and streaming video. In order to accurately

transmit many different types of data, numerous interfaces and

protocols have been created. When selecting the appropriate

equipment for your data communication application, it is

important to examine both your application and the

communication peripherals that must be incorporated into the

system. First, determine whether your application is best suited

for a wired system using cables or whether you need a wireless

solution. Also determine whether you need a portable system

using a laptop computer, or a desktop PC or Server. After deciding

upon your host computer, determine the ports available, and

the type of expansion boards this computer can best

accommodate. Then, decide which of those options will best

meet the speed and versatility demanded by your application.

Once you've selected an interface, you can then begin to look at

the type of data communication adapter you will need. You

must also consider the distance you will need between the

Data Communication Introduction

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Page 1 - Data Communication Explained

www.quatech.com10Data Communication ExplainedData communication is fundamentally a simple operation. PointA sends information to Point B and Point B

Page 2

1.800.553.1170Communication Overview19COMCompactPCI boards must follow one of two size specificationsand have ejector handles that are IEEE 1101.10 c

Page 3 - ISA and MicroChannel

www.quatech.com20PCMCIAExpanding Portable SystemsFounded in 1990, the Personal Computer Memory CardInternational Association (PCMCIA), of which Qu

Page 4

1.800.553.1170Communication Overview21COM20Mbps. The 2.1 spec. does not provide for bus mastering,DMA, or multiple interrupts, (however, Quatech&apo

Page 5 - Plug and Play

www.quatech.com22Cables and PortsThe Root USB Hub is connected directly to the USB Host, andfrom there everything is done with cables. Two types of c

Page 6

1.800.553.1170Communication Overview23COMThe Series A connector pictured (see bottom left) is for use withhigh speed (12 Mbps) devices, and can be up

Page 7

www.quatech.com24IEEE 1394The High-Speed Multimedia SolutionIEEE 1394 is a high-performance serial bus designed for highspeed audio, video and data tr

Page 8

1.800.553.1170Communication Overview25COMTo combat this timing problem, asynchronous communicationrequires additional bits to be added around actual

Page 9 - PCI and CompactPCI

www.quatech.com26Synchronous Communicationnot only that all devices in the system be synchronized witheach other, but also that each individual dev

Page 10 - Communication Overview

1.800.553.1170Communication Overview27COMit then establishes communication parameters that defineinstructions for processing given bit sequences. Fi

Page 11 - 16-Bit PCMCIA

www.quatech.com28The Information Frame is used when actual data is beingtransmitted. It is also used to provide sequencing, flow anderror control fun

Page 12

1.800.553.1170Communication Overview11COMcommunication peripherals and the host computer, as well asthe data transfer speed required for your applica

Page 13 - USB Features

1.800.553.1170Communication Overview29COMThe previous sections have discussed ways in which data istransmitted and received. However, we have yet to

Page 14

www.quatech.com30RS-232 and RS-422/485In order for DCE and DTE devices to communicate with eachother, two wires must be used--one for transmission a

Page 15 - IEEE 1394

1.800.553.1170Communication Overview31COMRS-422Balanced TransmissionThe RS-422 protocol greatly expands the practical possibilitiesof the serial bus.

Page 16

www.quatech.com32Parallel CommunicationIn the BeginningThe original 8-bit parallel port was developed by IBM in 1981 asa faster interface to dot matr

Page 17 - Synchronous Communication

1.800.553.1170Communication Overview33COMIntroduction to Spread Spectrum TechnologySpread Spectrum (SS) technology is not very new (relativelyspeakin

Page 18

www.quatech.com34DSSS and Bluetooth(Minimum Shift Keying (MSK))(DSSS Receiver)The IEEE 802.11b specification uses Binary Phase Shift Keying(BPSK) and

Page 19 - Isochronous

1.800.553.1170Communication Overview35COMA Short-Range Mobile SolutionBluetooth is a specification for a small form-factor, low-cost, short-range rad

Page 20

www.quatech.com36Application ExamplesQuatech's extensive data communication line is designed toprovide solutions for a wide range of serial and p

Page 21 - RS-232 and RS-422/485

1.800.553.1170Communication Overview37COMCentral BankComputerBranchPC-ServerHigh Speed ModemMultiple Quatech 2-PortRS-232 Serial PCI CardsMultiple te

Page 22

www.quatech.com38Portable ApplicationsAdding Serial PeripheralsAs with desktop systems, Quatech serial PCMCIA communicationcards and serial USB adapte

Page 23 - Parallel Communication

www.quatech.com12ISAIn The BeginningThe Industry Standard Architecture or ISA bus began as part ofIBM's revolutionary PC/XT released in 1981. How

Page 24

1.800.553.1170Communication Overview39COMRadiation Mapping with a PDAMapping radiation contamination after accidents or at wastedisposal sites demand

Page 25 - DSSS and Bluetooth

www.quatech.com40AirplaneCockpitQuatechMPAP-200/300SynchronousRS-422/485PCMCIA CardNotebookComputerWhen synchronous systems were first implemented the

Page 26

1.800.553.1170Communication Overview41COMData Communication Product Selection GuideUSB Product Features GuidePCMCIA Product Features GuideModel Protoc

Page 27 - Application Examples

www.quatech.com42PCI/CompactPCI Product Features GuideProduct Selection GuideModel Interface Protocol UARTSurgeSuppressionPorts Connector Cable PageDS

Page 28

1.800.553.1170Communication Overview43COMISA Product Features GuideModel Protocol UARTSurgeSuppressionPorts Connector Cable PageDS-100S RS-232 16550 n

Page 29

1.800.553.1170Communication Overview13COMsoftware to set these parameters are called Plug and Play. Whilethere is nothing inferior about using jumper

Page 30

www.quatech.com14PCIA New StandardFirst released in 1992, the Peripheral Component Interface (PCI)has rapidly evolved into a viable replacement for th

Page 31

1.800.553.1170Communication Overview15COMThe high speed data transfers across the PCI bus limits the numberof PCI expansion slots that can be built i

Page 32 - Communication Overview

www.quatech.com16Quatech guide to choosing a quality PCI communication boardThe PCI bus specification was designed to take the guessworkout of choosin

Page 33 - Product Selection Guide

1.800.553.1170Communication Overview17COMLook closely at the PCI card you are considering buying. Does it comply withall aspects of the PCI specifi

Page 34

www.quatech.com183.350" with out using riser cards. There are two types of LowProfile PCI boards: MD1 and MD2. Both are built on 32-bitaddressi

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