Datacom module 4: Fundamentals of Data Communication

Module 4Fundamental Concepts of

Data Communications

Chapter 22

Electronic Communications Sytems , Fifth Editon

By: Wayne Tomasi

ECE @Saint Louis University, Baguio City1

Prepared by: Engr. Jeffrey Des B. Binwag

Data Communication Codes

• Baudot Code

• ASCII (American Standard Code for Information Interchange)

• EBCDIC (Extended Binary Coded Decimal Interchange Code)

• Bar Codes

– Code 39

– UPC (Universal Product Code)

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Data Communication Codes

• Categories:

–Alphanumeric Characters

–Graphic Control Characters

–Data Link Control Characters

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Error Coding

• Error Detection. Involves monitoring data transmission and determining when errors have occurred.

– Redundancy Checking: VRC and/or LRC, CRC, Checksum

– Hamming Code

• Error Correction. Involves the correction of messages that have been determined by error detection codes to contain errors at the receiver.

– Retransmission

– Forward Error Correction: VRC/LRC, Hamming Code

– Symbol Substitution

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Character Synchronization• Character Synchronization. Involves identifying the

beginning and end of a character within a message or an extended bit sequence.

– Asynchronous Serial Data. Also known as start-stop transmission because each data character is framed between start and stop bits so that time gaps in between characters do not present a problem.

– Synchronous Serial Data. Generally involves transporting serial data at relatively high speeds in group of characters called blocks or frames with no lapses in between characters. A unique synchronization character is transmitted at the beginning of each message block as opposed to providing start and stop bits per character.

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Bit Synchronization

• Bit Synchronization. A process that ensures the transmission and reception of the same number of bits without errors and in the correct order without considering the relation of each bit to adjacent bits as part of a character or message. Such procedures include correct sampling as well as proper start-bit verification.

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Data Communications HardwareAll endpoints in a data communication network have three fundamental components namely:

• Data Terminal Equipment (DTE). Any binary digital device that generates, transmits, receives, and/or interprets data messages. (i.e.: LCU, STACO, ACIA, UART, USRT)

• Data Communication Equipment (DCE). These are equipment that interfaces data terminal equipment to the transmission channel. (i.e.: MODEM)

• Serial Interface. A communication line that ensures the orderly flow of data between a DTE and DCE. (i.e.: USB, RS 232)

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Two-point Datacom Circuit

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Universal Asynchronous Rx/Tx

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UART FUNCTIONS

• Parallel-to-serial at the Tx and Serial-to-parallel conversion at the Rx

• Error detection

• Framing

• Formatting

• Status monitoring

• Voltage level conversion/matching

• Bit and character synchronizationECE @Saint Louis University, Baguio City 11

UART Control Word

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UART Transmitter

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UART Receiver

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UART Receiver Start-bit Verification

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USRT Sampling Error

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USRT FUNCTIONS

• Parallel-to-serial at the Tx and Serial-to-parallel conversion at the Rx

• Error detection

• Synchronization

• Formatting

• Status monitoring

• Voltage level conversion/matching

• Bit and character synchronizationECE @Saint Louis University, Baguio City 17

QUIZ 2 COVERAGEAll Discussions in the book by Tomasi covering the following topics:

• Datacom Circuits

• Serial and Parallel Data Transmission

• Datacom Circuit Arrangements

• Datacom Networks

– Components, Functions, and Features

– Models

– Topologies

– Classifications

• Datacom Codes

• Error Coding

• Character and Bit Synchronization

• Datacom Hardware

• Datacom Circuits

• UART and USRTECE @Saint Louis University, Baguio City 18