Practical data communications and networking for engineers and technicians is a comprehensive workshop. It covers RS-232, RS-422, RS-485, industrial protocols, industrial networks and the communications requirements for 'smart' instrumentation. It will equip you with the tools to analyse, specify and debug data communications and networking systems in the instrumentation and control environment. This workshop is designed to benefit people who are involved in specifying, commissioning and debugging data communications and networking systems for instrumentation and control, but who have little previous experience in this area. It has been structured to cover the main concepts of data communications, to clarify their meaning and to describe their applications in modern process control and automation systems.

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Overview of Data Communications

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Topics
Introduction
Historical
Standards
OSI
Protocols
Physical Standards
Modern Instrumentation & Control

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Introduction
 Transfer of Information From One Point to Another
 Transmitter/Receiver/Link
 Serial Links vs Parallel Links
 Digital Data vs Analog
 Mutual Agreement

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Telegraph System
 Used Morse Code
 Plus and Minus Voltages
 CSMA/CD (Carrier Sense Multiple Access with Collision
Detection)
 Acknowledgement that the Message was Received

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Historical Background
Teletypes Needed Baudot Code
Equal Number of Bits for All Characters
Hardware Control Using Break Character
Positive Voltage Held Longer than One
Character
Baud Rate defined as the possible number
of changes in state per second

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OSI Model
 Developed by the ISO
 Universal Framework for Building A Communications Systems
 7 Layer Model
 3 Layer Model Very Common for Industry
 Missing the 8th Layer

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Standards Within A
Communications System
Code - Morse - Hex - ASCII
Physical - 232 - 422 - 485
Protocol - Modbus, Profibus, Hart,
Foundation Fieldbus, Ethernet
Open Systems Interconnection Model

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Common Codes
Hex - Used for “Number” Protocols
Only Has 0-9 and A-F Characters
Limited but Very Efficient
ASCII - Used in Most New Protocols
Has All the Letters, Number and
Punctuation
High Overhead but Very Versatile

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Representation of the OSI Model

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Protocols
 Rules for Transmission of Data (Packets)
 Packet Can Include:
 Sync Byte
 Destination Address
 Source Address
 Data
 Error Detection
 Modbus - Profibus - Canbus - Ethernet - TCP/IP
 HDLC - DH+ - HART - DNP3 - Interbus - FTP

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Basic Structure of an Information
Frame Defined
Sync
Byte
Destination
Address
Source
Address
Data to be
Transmitted
Error Detection
Byte
 SYNCHRONIZING BYTE Is Used To Synchronize The Receiver.
 DESTINATION ADDRESS Is Where The Packet Is Going.
 SOURCE ADDRESS Is Where The Packet Has Coming From.
 DATA Is The Information Contained In The Packet.
 ERROR BYTE Is The Result Of The Error Correction Calculation.

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A Typical Serial Data
Communications Link
RS-232 RS-232
Terminal Modem
Transmitted Data Received DataAnalog Signal
Modem Communication Link Terminal
DTE DCEDCE DTE
• DTE = Data Terminal Equipment
• DCE = Data Communication Equipment

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Voltage Standards
EIA/RS-232 Interface Standard
Half / Full Duplex - Point to Point
EIA/RS-422 Interface Standard
Full Duplex - Point to Point
EIA/RS-485 Interface Standard
Half Duplex - Multidrop

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Modern Instrumentation
 Distributed Control System (DCS)
 All Electronic
 Programmable Logic Controller (PLC)
 Came from Relay Equipment
 Smart Instrumentation
 Intelligent Electronic Devices ( IED )
 Super Smart Sensors

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Distributed Control System
Based Around a Data Highway
Modular Distributed & Integrated
Each Module Performs Specific Dedicated
Task
“Good” on Analog Control
Easy Connection to PLC’s / supervisory
Computer Interfaces

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PLC
 Programmable Logic
Controller
 Sequence Control and
Interlocking
 On/Off Inputs/outputs
 Ladderlogic Type
Programs

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A Typical PLC System

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Smart Instrumentation
Microprocessor Based Instrument
Embedded Controllers
Data Communications Capability
RS- 232, RS 485 or Fiber Optic
Ability to Multi-drop With Other
Instruments on Same Highway
Wave of the Future...Eg Fieldbus

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Graphical Representation of A
Complete System
Top Layer is Ethernet
Lower Level is RS-485 Data Highway
Network, RS-232 and Fiber Optic
DCS Data Highway
Interconnects Using a Gateway
(See Figure 1.5 Page 13)

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