INDUSTRIAL FIELDBUSES

The term « Field bus » has been used for ten of years while industrial networking has been evolving continuously. Consequently, it has been used ( and will be used ) in many ways so that it became confusing and it is difficult to understand what it means nowadays. Historically, it was talked of data bus in the sense of a point to point short linear path where data are transmitted serially. With the time, hardware get higher performance, data have been multiplied, data exchange requirements too, while they avoid some cabling. The result is that the number of communicating devices increased and the number of transmission paths too.

The usage has perpetuated to give the name of bus to some communication technology, but right now can still a digital communication network owning many stations and many data sources be qualified as a field bus ? ( And more generally, what can be the notions included in the terms « bus » or « data bus » ? Does a « bus » constitute a « network » ? Does a « network » constitute a « bus » ? Does the term « network » result from an abbreviation for « data bus network » ? ).

Which among HART, Modbus, Profibus, IO-Link, Ethernet-IP, Ethercat or Powerlink are or are not field buses for instance ? Is this term in relation with one specific applications such as process control, motion control, manufacturing automation or machinery automation ? Is it related to boolean devices only, or to analogical devices only, or to sensors and actuators only ? Does it include the SCADA systems ? Is a field bus based on a specific technology ( RS485 or RS232 ), on a specific architecture ( master / slave, token bus ) or on a specific medium ( copper cable for instance ) ? Are sensor Ethernet networks or wireless device networks field buses ? Does a field bus depend on its performance ? Can a 1 Gbps Ethernet field network be named a « field bus » just because it interacts with sensors and actuators ?

And what about the term « field level » ? Where does the field begin and where does the field stop ? Does an electrical cabinet stay at the field level ? Must any data client accessing a field bus be at the field level ? Or only the devices providing the data ? And what about the topology ? Does a field bus use a single linear topology only ? Can a network be a field bus when using a star topology or a ring topology ?

A definition could be : a « field bus » is a network which access directly to the sensors and to the actuators, offering medium performance and rather universal capabilities. But how acceptable and how pertinent is this definition ?

« ARCNET » is not a well known technology, despite the fact it has been embedded in many industrial proprietary field buses, in many office automation networks and that more than 22 million of nodes have been sold until 2014.

Like Ethernet and Controller Area Network ( CAN ), it is a data layer only technology ( the application layer is not specified and even not mentioned ). Thus, while developing a new network, engineers used the Arcnet technology to build the data layer, and they programmed their own application layer, usually without to mention that the Arcnet technology was embedded in their products. Consequently, the network foundations were not visible to the user.

The ARCNET networks are structured over a bus topology or over a star topology, using the token technology to manage and to synchronize the data exchanges. The token technique is particularly convenient for the digital automated production networks, and it is often found in automated applications related to industrial control, robotics and transportation.

You will find here the official and detailed presentation about this embedded real-time network. You will discover in an essential way what it is talked about, what is the history of this very popular deterministic field bus, what are its characteristics, and which benefits the main programmable logic controllers makers and their clients could wish. You specifically can consult there all the details concerning the specifications of the protocol, the available topologies and the supported media and you can also download there the standard specifications ( ANSI 871.1 and ANSI 871.2 ) plus the tutorial written by the « Arcnet » consortium.

The token technique used by Arcnet   is a widespread data transmission synchronization technology, especially adapted to industrial digital networks. This technique is known as token ring, token network and token bus.

The network manager ( or the master ) puts in circulation a single token which is distributed successively to each connected device. Once all the devices have transmitted their data, a new tour is initiated ( hence the term of « ring » ).

• At a given time, the device which has got the token is the only one authorized device to transmit the data over the network.
• Once the transmission has been finished, or whether there are not any data to transmit, the device informs the manager it has finished.
• Then, the manager distributes the token to the next device.

  The location is not taken in account : the next node can be located anywhere in the respect of the limits imposed by the network.

This mechanism warrants there will never be any risk of collision during the transmissions. Features like priority management can be implemented easily and work fine with this technique. Using the token technology helps to get deterministic behaviour and real time features.

« BITBUS » is a field bus based on widespread and well known technologies such as RS485 serial communications. It is a simple master / slave network allowing a master to talk with up to 249 slaves. This digital communication network is an international standard referenced as IEEE 1118.

• Fundamental knowledge before starting a BITBUS Project.

  This document presents a specification overview, the structure of the frames and the structure of the messages, access mechanisms to input, output and memory, the slave tasks and an annotated list of the command codes and of the error codes. Here you will also discover an installation guide, helping you to setup devices on the network, describing how cabling the connectors of the RS 485 serial line and how to choose the resistor for the end of the line.

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• Bitbus specifications, programming and using the IEEE 1118 standard.

  The users consortium offers downloading various official documents freely. These papers are relative to development, installation and usage of applications embedding its technologies. You will find there user documentation and the full programming interface, technical specifications for the interface between Ethernet TCP networks and the Bitbus network, the specifications for message diffusion, how to design an optic fibre interface for this network etc …

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• Bitbus network full technical specifications. ( )

  This document - originally written by the INTEL company - presents all the technical specifications for these networks, from a physical point of view and from a logical point of view.

  • The physical specifications consist in network topology, in slave devices, in repeaters, in synchronous mode and in electronic interfaces associated with signal synchronization diagrams.
  • The logical specifications concern the different frames, the data exchange ( proceeding ans synchronizing ), the message transfer protocol, the memory management and the command management.
  • As for the devices, you will find there the emitting and receiving interfaces specifications.

www.bitbus.org

« CC-link » ( Control and Communication Link ) is a field network that processes control and information data at high speed with a deterministic behaviour, intended for factory and process automation. This network was originally developed by the Mitsubishi Electric company with more than 4 million installed nodes. The CC-link family consists of CC-link open field network, CC-Link LT ( dedicated to sensors and actuators networking ), CC-link safety and CC-link IE ( 1 Gbps Ethernet based fieldbus with two savours : CC-link IE control and CC-link IE-field ).

• The original version - A fast field bus.

  In its first versions, this is a field bus which uses RS 485 serial link at 10 Mbps, and manages up to 64 connected devices. This summary resumes its earliest technical features such as the topology, the amount of access points per stations, the performances, and the limits of cabling.

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• CC-link IE - A 1 gigabit industrial Ethernet network.

  This folder displays the >main features of the network in its two versions, « CC-link IE control » and « CC-link IE field », that is the performances, the targeted automation applications, the ease of maintenance and diagnostic tasks.

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• You can also read an overview of the CC-link LT network dedicated to motion control applications, and an overview of the CC-link safety network, which is a high speed network dedicated to safety.

www.cc-link.org

« CIP » ( Common Industrial Protocol ) is an object oriented network system which is the base of the end users industrial networks of the CIP family. Each object has attributes ( the data ), services ( the commands ) and behaviour ( the reactions to events ).

Since CIP-based networks ( CIP, ControlNet, DeviceNet, Ethernet IP, CIP safety, CIP motion, CompoNet and many other extensions ) are based on a common application layer, the application data remains the same whatever the network. The application programmer does not even need to know to which network a device is connected.

ODVA is a manufacturer association which supports all the Common Industrial Protocol ( CIP ) based networks. The organization manages the development of the technologies and assists the CIP networks users by providing utilities and training support.

• CIP Technology Overview.

www.odva.org

« EtherNet/IP », is an Ethernet CIP based network. It is the base of ControlNet too. As with all CIP networks, it is based on the Session layer of CIP and the other layers above. The transport layer has been adapted according to the Ethernet standard.

• Introduction to Ethernet IP.

  This is an overview presenting the architecture, the topology and the main features.

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• Technical documentation on Ethernet/IP, CIP, ControlNet and many others ODVA network technologies. ( download library )

  Design, architecture, addressing, recommendations, implementations and installation of industrial networks based on this standard. Particularly, you will be able to download the Ethernet IP infrastructure guide ( ).

www.odva.org

« Foundation Fieldbus » is a real time open protocol and architecture which has been especially designed to control process and manufacturing applications, with the particularity of communicating directly with instrumentation devices.

It is an full digital communication standard, since it exchanges only digital data, without the need of any 4-20 mA loop, nor any else analogical signal. In other words, it is a protocol embedded into some instrumentation networks and this « network » basis is called a « field bus » ( But really, what is a field bus ? ).

Natively, this industrial communication system uses some widespread standards, such as the Function Block Model, EDDL ( Electronic Device Description Language ), FDI ( Field Device Integration ) and FDT ( Field device transmitter ). The main versions fo these networking techniques are « Foundation Fieldbus H1 » ( the earliest one ), « Foundation Fieldbus HSE » ( High Speed Ethernet, a Fast Ethernet based network ) and « Foundation Fieldbus SIF » ( Safety Instrumented Functions )

The Fieldbus Foundation organization provides some educational informations on its technologies, with the specifications, tools, training and many more.

• Technology overview.

  This page resumes the technology and what are its advantages. You can also get a file introducing briefly to the technology.

• Technical references.

  You can download here several technical papers. The white papers are articles which focus on particular matters or point of view related to Foundation Fieldbus. The technical guides are some more practical documents such as the wiring and installation guide or the system engineering guidelines.

www.fieldcommgroup.org

• Fieldbus and Fieldbus HSE technical overview.

  You can download here the description of the technology, all of these documents are intended for the users ( File « FF primer » in .pdf file format ). This document presents the network architecture according to the OSI model, the topology, the physical characteristics of the signal and the ways of communication. It also talks about the function blocks, about the description and the configuration of the devices, and about alarms and communication management. It finishes with a detailed description of the High Speed Ethernet Fieldbus ( Fieldbus HSE ).

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• Papers and technical guides.

  You can get here a manual to help you for cabling and a guide to assist you for your first Fieldbus Foundation network installation. You will also find technical informations about Fieldbus HSE and about the concepts used for redundancy with the Fieldbus H1 networks.

www.fieldbusinc.com

« FIP » ( Factory instrumentation protocol ) has been designed as a entirely digital real time network from a node to another. It allows to connect all the devices of an automated plant ( controllers, operator panels, sensors, instrumentation, actuators, inverters etc ). The main characteristic of « WorldFIP » is the usage of a single and simple protocol in order to answer real time communication requirements and to answer background communication requirements for a complete control system or for a complete instrumentation system.

The « FIP » protocol has been created by the « Alstom » company, ant its « WorldFIP » extension has been registered as a European standard with the reference « EN 50170 ». Despite the fact that the « WorldFIP » user association has been dissolved in 2007, the CERN in Geneva ( Switzerland ) has installed more than 450 kms of WorldFIP cables in order to connect about 12 000 nodes, which are controlling parts of the current LHC plant, the « large hadron collider ».

In its first part, this detailed protocol introduction ( 29 pages ) shows the fundamentals principles, the structure used for communication, the performances and the available topologies. The second part introduces the « FIP » model and the distributed real time data base ( description of the client-server model, of the producer-consumer model etc … ). The last part describes the « IP » structure, according to the OSI layer model.

You will also find some other informations about the FIP industrial network into the open hardware organization website hosted by the CERN ( Nuclear Research European Centre ).

ALSTOM company

This document of about 25 pages presents this technology, beginning with the description of the electronic components and with the description of the communication controller. Then, you will find a description of the communication libraries, and finally the presentation of some « WorldFIP » dedicated utility software.

www.dia.uniroma3.it

According to the OSI layers, these specifications describe what are the different layers in use and how do they apply :

• The physical layer.

  Configuration, transmission, speed, coding.

• The data link layer.

  Addressing, bus arbitration, buffer management, acknowledgement, frames.

• The application layer.

  Reception / transmission, read / write, resynchronization, variable types, protocol data units - PDU, organization.

This document of specification defines also the protocol, how to manage the network with local services, with remote services, and with multiple applications. The last section carries on security. It presents the mechanisms used to manage the medium redundancy, the detection of errors in the physical layer, and how frame checking is sequenced.

J. DE AZEVEDO, N. CRAVOISY - WorldFIP

MODBUS Protocol is a messaging structure developed by Modicon ( now part of the Schneider Electric company ) in 1979, used to establish master-slave / producer-consumer communication between intelligent devices.

This digital networking system is used to establish a master-slave and provider-customer communication between smart devices. It is declined in several versions ( ASCII, RTU, TCP, Modbus Plus and ModBus Plus I/O ), the versions we can meet the most often are the following :

• The Modbus RTU protocol is a point to point ( peer to peer ) protocol using a communication serial line ( RS 232, RS 485, RS 422 etc ) as data transmission support. The basic item in the frame is a byte with 8 significant bits.
• The Modbus TCP protocol is an adapted version embedded into the Ethernet protocols, following the client-server model instead of the master-slave model used in the RTU version.

This freelance automation engineer introduces the main features of the Modbus protocols. He compares the properties of Modbus ASCII with the properties of Modbus RTU, then he describes the addressing and the most used requests.

Lammert BIES - www.lammertbies.nl

This folder provides a set of technical resources in relation with all the different variants of the Modbus networks.

• You can get the specifications for all the versions ( Modbus RTU, Modbus TCP, Modbus Plus etc ) edited by the foundation.
• You can access white papers, external links and resources dedicated to this standard, such as frames analysers, devices simulators and more.
• You will particularly find communication libraries written in various programming languages for many environments ( to embed code in your own programmable logic control software, a MMI, a PLC or a real-time data base application for instance ).

Modbus foundation - www.modbus.org

• Modbus Plus Planning and installation guide. ( )

  This installation guide introduces the Modbus Plus network and describes its composition and its performances. It states the connecting rules and finishes with the Modbus Plus transactions rules and the routing rules.

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• Modbus Plus IO Service Guide. ( )

  This manual presents the Modbus Plus IO network ( its architecture, its connections and how its messages are managed ), what are the options of configuration it provides and how to use the network with several controllers.

Schneider Electric

« PROFIBUS » is a widespread open communication system often met in factory automation and in process automation. It is convenient for fast and real-time applications moreover for complex communication usages. The Profibus family include several versions, related to well defined applications such as Profibus-DP ( decentralized peripherals ), Profibus-PA ( process automation ), Profinet ( Profibus over Ethernet ), Profidrive ( motor drives and frequency inverters ), Profinet IO and many more.

• Profibus technology and system description. ( )
• Profibus - An overview on the network technology.

www.profibus.com

Profinet is quite the universal field bus in the Profibus family, since Profinet is a declination of the Profibus system running over Ethernet. Thus, Profinet benefits of the Ethernet features and of the advantages of industrial Ethernet. Consequently, Profinet can satisfy all the needs of automation applications, and can be used for factory automation, process control, safety applications and motion control.

This is a brief introduction to the technology.

You can get more technical details in the Profinet system description file. ( )

www.profibus.com

« SafetyNET-p » has been developed by the PILZ company as a deterministic real-time Ethernet intended to industrial environments, in order to operate their most critical functions safer. This system is an evolution of the « SafetyBUS-p » safe bus system, also created by the same company. Their application layer is based on the CANopen control network application layer.

This standard is a multi master Ethernet-based field bus system intended to industrial automation networking. Its objective is to enable real-time communication and to provide data exchanges in the same time.

In these slides, Sharani Sankaran presents the physical layer and two of its components : the real time frame line ( RTFL ) and the real time frame network ( RTFN ).

• RTFL operates for fast intracells communication in relation with RTFN. The RTFL topology is based on a linear topology, transporting data over standard Ethernet frames.
• RTFN allows SafetyNet-P to be used within standard Ethernet networks by using standard hardware and software, with respect of real-time requirement.

Then the author presents the communication model composed of two separated channels : the cyclic data channel ( CDC ) and the message channel ( MSC ).

• Before all, a CDC channel is used to transfer cyclic process data. In RTFL, it is a reserved data range in the Ethernet frames. In RTFN, it is based on a repeated sequence of point to point dialogues.
• A MSC channel is used for non cyclic data transfer, essentially for diagnostic purpose. Transferred data represent exactly one frame per communication cycle.

Then, you will read a short presentation of the communication management, followed by the application layer description. The Safetynet P application layer is based on the CAN open application layer, and transmit data using PDO data containers ( typically in CDC channels ) and SDO services.

Finally, after the clock synchronization presentation, it is talked about the safety communication model, the safety communication layer and the safety application layer. They have in charge to detect faults in order to prevent failures of critical processes. The safety layers implement safety in data transmissions and maintain the integrity of the communication channels. They represent what is essentially specific to Safety-net networks - somewhere, they could be considered as its fingerprint - compared to other common field bus.

Sharani Sankaran

This open field bus standard is a serial data transmission ( RS-232 / RS-485 ) based on the CAN bus system. It is intended to operate highly safe communications between critical systems, specifically for security devices such as emergency stops, security gates and so on, depending on the features and depending on the critical requirements of the plant. Mainly, the loss, repetition, corruption or delay while transferring data will be detected. Whether an error occurs, the related I/O group is being stopped, or / and not allowed to start.

By now, the SafetyBus-p technology has been developed in a more modern way through the Ethernet based ( with some of CAN features ) Safety Net p technology.