PROFIBUS Manual - Max Felser - ebook

PROFIBUS Manual ebook

Max Felser

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Opis

In the last 20 years I have been personally involved with PROFIBUS: teaching it at the University, working on projects and leading workshops for industry. During this time, various descriptions and guides to different aspects of PROFIBUS were developed. I was helped in this by the contacts I had with industry and a range of experts in my capacity as chairman of PROFIBUS Switzerland and head of the PROFIBUS Competence Centre (PICC) at the Bern University of Applied Sciences. I have now brought these documents together in the form of a manual. Its purpose is to simplify entry to the world of PROFIBUS for a wider public. Now I generated an electronic book version with active links for the usage on iPad or Android tablet computers.

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PROFIBUS Manual

A collection of information explaining PROFIBUS networks compiled by Max Felser

In the last 20 years I have been personally involved with PROFIBUS: teaching it at the University, working on projects and leading workshops for industry. During this time, various descriptions and guides to different aspects of PROFIBUS were developed. I was helped in this by the contacts I had with industry and a range of experts in my capacity as chairman of PROFIBUS Switzerland and head of the PROFIBUS Competence Centre (PICC) at the Bern University of Applied Sciences. I have now brought these documents together in the form of a manual. Its purpose is to simplify entry to the world of PROFIBUS for a wider public. Now I generated an electronic book version with active links for the usage on iPad or Android tablet computers.

This manual will give answers to the following questions:

What is PROFIBUS?

For any first contact with PROFIBUS, I recommend starting with the introduction chapter, which introduces the structure of the PROFIBUS system.

How is PROFIBUS used?

End users will find a step-by-step planning guide and detailed guidelines about PROFIBUS installation.

How does PROFIBUS work?

Experts will find detailed descriptions of the different protocols, including lists and tables with different coding for the different layers of protocols.

How do I get a PROFIBUS Interface?

Developers of the field devices will find some practical hints about the evaluation and dimensions of a PROFIBUS interface.

Although all information and details in this document have been carefully checked, no responsibility can be assumed for any errors in this document or for damage arising from them. Brand names are used in this document with no claim of derivation.

Imprint:

PROFIBUS Manual by Max Felser

Edition 1.2.2 published at Thursday, August 09, 2012 by epubli GmbH, Berlin, www.epubli.de

© 2012 Max Felser

ISBN 978-3-8442-2946-2

Introduction

This chapter shows the fundamental way in which a PROFIBUS system is structured and where to find the standards for individual parts. An additional section sets out how a PROFIBUS system should be planned and the tools available for this purpose.

System structure

PROFIBUS defines the technical features of a serial field bus system, by which distributed digital automation devices, from field to cell level, can be networked together. PROFIBUS is a multi-master system and so allows the combined operation  on one bus of several automation, engineering and visualization systems with remote peripherals. PROFIBUS achieves this by differentiating between various device types.

PROFIBUS is based on recognized, international standards. Protocol architecture follows the OSI (open system interconnection) reference model, according to the international standard ISO 7498.

The standard requires each layer of transmission to take on precisely defined tasks: layer 1 (Physical Layer) defines the physical side of transmission , layer 2 (Data Link Layer) defines the bus access protocol  and layer 7 (Application Layer) defines application functions. Application profiles (User Layer) determine how communications functions should be used in different device classes and applications.

Layer

Name

Content

(Layer 8)

User Layer

Profiles

Layer 7

Application Layer

DP / FMS protocol

Layer 2

Data Link Layer

FDL protocol

Layer 1

Physical Layer

Transmission technology

Structure according to the OSI reference model

PROFIBUS offers different services for automation technology: cyclic data exchange  for process data and acyclic data exchange  for parameter setting data.

Stations

PROFIBUS differentiates between the following station or device types:

Masters determine data traffic on the bus. A master can send messages without an external request if it is in possession of the bus access token. Masters are also described as active stations.

Slave are peri­pheral devices, such as input and output devices, valves, drives and transmitters. They do not receive a token authorizing bus access. This means that they can only acknowledge messages received or, at the request of a master, send messages to it. Slaves are described as passive stations. They only require a small portion of the bus protocol, which means they make implementation possible with little effort.

Masters and slaves can be used for different protocols, such as

•FMS (field-bus message specification)

•DP (decentralized peripheral)

For this reason, the relevant protocol is often prefixed to their name:

An FMS master controls a relationship with an FMS slave. This is not further explained in the present volume.

The DP master controls a DP system. The DP slave is part of a DP system.

The DP master can assume different functions in a DP system. These functions are known as classes:

DP master, class 1:

These masters are controllers of a DP systems and the DP slaves assigned to it. Typically they will be controllers, PLCs or PC based systems.

DP master, class 2:

These masters are tools for commissioning, engineering and maintenance. They allow programs to be loaded  into controllers and DP slaves to be diagnosed and their parameters set. Typically they will be PC based systems.

DP master, class 3:

Is a clock master and distributes time.

Structure of a DP system

Every station - master or slave - in a DP system has a unique address.

Addressing stations

Every PROFIBUS station must have a unique address for communication. These PROFIBUS addresses are coded in one byte and comprise the range 0 - 127. However, individual address values are reserved and no longer free to be assigned.

Address

Use

0

is reserved as a rule for diagnostic tools, such as programming devices

1 ... n

Master station addresses should start with the lowest address. A single master will therefore have address 1.

Additional master stations will have addresses 2, 3... etc.

n ... 125

This means that, in a PROFIBUS network with one master, no more than 124 addresses will be left free for slave stations.

126

is reserved as a delivery address (default) for stations whose address can be adjusted via the bus. This is explained in more detail in the chapter on address changes.

127

is reserved for addressing all or groups (broadcast) and cannot therefore be set for one station.

Infrastructural components like repeaters, couplers and fibre optic (FO) converters transmit telegrams transparently from one segment to another and therefore do not require their own address.

Relationships

Individual stations in a DP system have a variety of relationships with each other:

Relations in a DP system

These individual relationships between masters and slaves (MS) have different tasks and properties:

Cyclic data transmission:

DP master, class 1 with DP slave cyclic with DP-V0 protocol used

Acyclic data transmission:

DP master, class 1 with DP slave acyclic with DP-V1 protocol used
DP master, class 2 with DP slave acyclic with DP-V1 protocol used

The above illustration also includes a relationship between masters (MM). This is only used very rarely in practice and is therefore not described in greater detail in this volume. You will find further information about this relationship is chapter 9 of Manfred Popp's book.

The different stations have implemented individual protocols in their structure:

Protocols in a DP system

Cyclic process data

A controller designated by PROFIBUS as master class 1 will control its remote peripherals in a cyclic exchange of data. This is called an MS0 relationship and is explained in detail in chapter 4.

In an initialization phase the controller will initialize each peripheral device and also check during cyclic data transmission whether the peripheral device, which has been designated by PROFIBUS as a slave, remains addressable.

For its part, the slave monitors whether the controller remains active with a response monitoring watchdog.

Phase:

Actions:

Diagnosis

The controller sends diagnostic requests to all project slaves

Initialization

The controller sends parameters to and checks the configuration of all project slaves

Data exchange

The controller sends output data and receives input data. Response monitoring and evaluation of diagnosis.

Phases in an MS0 relationship

During initialization the controller delivers initial parameters to the slave and checks the slave configuration. This configuration defines how much data will be exchanged in cyclic data traffic between master and slave.

In cyclic data exchange the master sends its output data to the slave and receives input data in reply. The PROFIBUS network for cyclic process data is therefore like a distributed process image of the controller.

The minimum cycle time can easily be estimated if the number of input and output bytes is known:

Where

N.B.: More precise formulae can be found in the chapter on cyclic data.

In a PROFIBUS network, there must always be at least one class 1 master present. However, several class 1 masters may also be on the same cable. This means that they will share the bit rate, i.e. the cycle time will be longer accordingly. A slave can only be controlled by one class 1 master!

These basic functions for cyclic process data are known as DP-V0. With protocol extensions DP-V1 and DP-V2, it is possible to fix the controller's cycle time to a specific value (equidistant cycle) and, with special telegrams, even synchronize the slave's cycle time with the PROFIBUS cycle (isochronous cycle).

If an application requires two slaves to exchange data directly with each other, the DP-V2 protocol will be needed. These protocol extensions allow data to be exchanged directly between slaves.

Acyclic parameter data

In any installation it is frequently necessary to adjust device parameters during runtime. For this purpose, PROFIBUS provides communication with acyclic parameter data.

A parameter master, which PROFIBUS calls a class 2 master, can establish a connection with a slave and exchange data acyclically. This is known as MS2.

Several class 2 masters may exist in a network alongside the class 1 master or masters and can simultaneously exchange data with the same slave. Any class 1 master can also simultaneously be a class 2 master.

Any class 1 master that has a cyclic MS0 relationship with a slave can also exchange data with it acyclically as MS1. In addition, an alarm model has been defined. Each slave has a status machine for alarms and checks the variously caused incoming and outgoing alarms, verifying acknowledgement by the class 1 master.

These protocol extensions for acyclic data exchange are part of the DP-V1 extensions and are optional.

Functional scope

PROFIBUS technology is modular in structure. This allows individual versions of a function group to be selected and ensures flexibility in adapting the properties of a PROFIBUS network to requirements.

Application profiles

Process automation (PROFIBUS-PA), manufacturing technology

Device profiles

ProfiDrive, ident systems, ....

General profiles

PROFISafe, redundant systems

Protocols

FDL, DP-V0, DP-V1, DP-V2

Transmission

Electrical (RS-485), optical (FO), intrinsically safe (MBP)

Functional scope of individual levels

Transmission methods

The standard includes three different methods of data transmission:

•asynchronous electrical transmission as RS-485 for general purposes

•synchronous electrical transmission with the option for intrinsically safe transmission and supply via the bus, intended above all for process automation.

•optical transmission via glass or synthetic fibres for overcoming long distances, potential differences, or strong electromagnetic contamination.

Alternative methods of transmission, such as wireless radio, wireless optical, slip-rings, etc. are available from a variety of manufacturers.

Protocols

The fieldbus data link (FDL) protocol is common to all levels of PROFIBUS development. Not all FDL services are required for every function.

The decentralized peripheral (DP) protocol is available in three expansion levels. Each level of expansion adds further functions. Most of these additions are optional.

Protocol - functions (master or slave):

V0

V1

V2

Cyclic data exchange MS0

m

m

m

Acyclic data exchange with class 1 master (MS1)

-

o

o

Acyclic data exchange with class 2 master (MS2)

-

m

o

Alarm messages

-

o

o

Fail-safe protocol (PROFIsafe)

-

o

o

Isochronous cycle

-

-

o

Time synchronization

-

-

o

Time stamp

-

-

o

Direct data exchange (data exchange broadcast)

-

-

o

Integration technologies (slave):

V0

V1

V2

Diagnostic messages from devices

m

m

m

GSD files for configuration

m

m

m

Engineering with EDD

-

o

o

Engineering with FDT/DTM

-

o

o

Engineering with tool calling interface (TCI)

-

o

o

A device will frequently be designated by its expansion level: a DP-V1 master or a DP-V0 slave. This is for information purposes only. In particular, the designation DP-V2 will not be found in the IEC standards.

Profiles

A profile defines the behavior of a type of device or a type of application. It restricts the degrees of freedom of selection of PROFIBUS communication, i.e. it defines which subset or expansion level to implement.

Standards and guidelines

From the beginning, PROFIBUS definitions have been incorporated in standardization. The creation of standards is subject to fixed rules and is a process that often lasts many years. For flexibility of response to market requirements, the PROFIBUS organization publishes additional definitions in the form of guidelines.

Standardization

The PROcess FIeld BUS (= PROFIBUS) standard was established in Germany in 1989 and 1991 as DIN 19245, parts 1-4. These standards are only available in German and, unfortunately, not in electronic form.

Number

Name / content

Edition

DIN 19245 part 1

PROFIBUS-FDL (fieldbus data link)

1989

DIN 19245 part 2

PROFIBUS-FMS (fieldbus message specification)

1990

DIN 19245 part 3

PROFIBUS-DP (decentralized peripherals)

1994

DIN 19245 part 4

PROFIBUS-PA (process automation)

1995

In 1996 all European fieldbuses were combined under a single standard: EN 50170. Every bus system is covered by one part. PROFIBUS is covered by part 2, which is itself divided into 9 sub-categories. The Application Layer here comprises the PROFIBUS-FMS protocol and PROFIBUS-DP is designated as the User Layer.

Number

Part

Name / content

EN 50170-2

General Purpose Field Communication SystemPart 2: PROFIBUS

Part 1

General Description of the Normative Parts

Part 2

Physical Layer Specification and Service Definition

Part 3

Data Link Layer Service Definition

Part 4

Data Link Layer Protocol Specification

Part 5

Application Layer Service Definition

Part 6

Application Layer Protocol Specification

Part 7

Network Management

Part 8

User Specifications

Part 9

Physical Layer and Data Link Layer for Process Automation

In 1999, this European standard was adopted with 7 further fieldbus systems as international standard IEC 61158, with the effect that since 2007 EN 50170 it is no longer formally in force.

In 2002 activities to update IEC 61158 came to an end. In the course of these activities, the most recent developments of PROFIBUS and PROFINET were taken into account within the standard. IEC 61158 bears the title: "Digital data communication for measurement and control – Fieldbus for use in industrial control systems" and is divided into 6 parts designated as 61158-1, 61158-2 etc. The content of part 1 is concerned with introductory topics, while subsequent parts follow the OSI layer model (layers 1, 2 and 7). The different parts of IEC 61158 specify, among other things, numerous services and protocols for communication between bus stations, which are to be viewed as the total available set and from which a specific subset is selected for particular fieldbus systems.

IEC 61158 takes account of the existence on the market of numerous different fieldbus systems by defining 22 fieldbus protocol types, which it designates as types 1 to 22. PROFIBUS is assigned to type 3 and PROFINET to type 10. IEC 61784 bears the title: "Profile sets for continuous and discrete manufacturing relative to fieldbus use in industrial control systems". IEC 61784 sets out which subsets of the total available set of services specified in IEC 61158 (and other standards) are used by any particular fieldbus system for communication. The fieldbus-specific communication profiles defined in this way are assembled into communication profile families (CPFs), according to their use in the individual fieldbus systems.  The profiles used by PROFIBUS are to be found in "Family 3", which is subdivided into 3/1 for DP and 3/2 for PA. In the second edition, valid from 2003, a further profile 3/4 for PROFINET CBA has been defined within the same family.

Number

Part

Name / content

IEC 61158

Digital data communications for measurement and control - Fieldbus for use in industrial control systems

1

Introduction

2

Physical Layer specification

- Type 1 for PROFIBUS-PA

- Type 3 for PROFIBUS-DP

3-3

Data Link Layer service definition

- Type 3 for PROFIBUS

4-3

Data Link Layer protocol specification

- Type 3 for PROFIBUS

5-3

Application Layer service definition

- Type 3 for PROFIBUS

6-3

Application Layer protocol specification

- Type 3 for PROFIBUS

Number

Part

Name / content

IEC 61784

Digital data communication for measurement and control

1

Profile sets for continuous and discrete manufacturing relative to fieldbus use in industrial control systems

PROFIBUS-DP is profile CPF 3/1PROFIBUS-PA is profile CPF 3/2

In autumn 2007 new editions of the IEC 61158 and IEC 61784-1 standards were published. Their structure has been so simplified that now, in the case of IEC 61158, all documents for the different types can be purchased separately. This means that type 3 only is necessary for PROFIBUS. In addition, further profiles have been defined for PROFINET IO (3/5, 3/6 and 3/7).

A list of the most important IEC standards for PROFIBUS can be found here.

Guidelines

For further definitions, guidelines have been specified by the PROFIBUS organization. These guidelines are available free-of-charge from the webside of PROFIBUS and PROFINET International (PI). for members of a Regional PROFIBUS and PROFINET Association (RPA).

Guidelines numbers cover the following areas:

•Numbers 0.xxy : PROFIBUS Standard

•Numbers 1.xxy : PROFIBUS Guidelines

•Numbers 2.xxy : PROFIBUS Profiles

•Numbers 3.xxy : Profiles

•Numbers 4.xxy : Descriptions

•Numbers 6.xxy : Lists of IDs (on-line)

•Numbers 7.xxy : PROFINET

•Numbers 8.xxy : Manuals

The final character (y) defines the language of the document:

A summary of all PROFIBUS International guidelines can also be found here.

System planning and commissioning

With a systematic approach to the planning, commissioning and maintenance of a PROFIBUS network, errors can be avoided and expense reduced. We recommend the following tried and tested steps:

Step

Description

1. Prepare

1.We select which field devices we wish to use in our automation task.

2.We collect the General Station Description (GSD) files for our chosen field devices. This lets us know what properties the devices used have.

3.The GSD files are loaded into the library of the planning tool.

2. Plan

1.The system is planned by assigning field devices to the controller.

2.Controllers and field devices are configured. The individual stations are taught by the configuration who is supposed to communicate and exchange data with whom.

3.Controllers and field devices are parametrized. The individual parameters define how specific functions are to be executed within the devices.

3. Install

1.The network is constructed with the distances and number of repeaters.

2.Cable is laid on a correct route.

3.Cables are connected with suitable connectors.

4.The installation is checked.

4. Commission

The PROFIBUS network must be commissioned systematically.

5. Monitor

1.All devices supply diagnostic information. Rigorous interpretation and assessment of this information assists in locating faults.

2.Field devices can report their status with diagnostic information.

3.The quality of data transmission on the PROFIBUS can be monitored.

Step 1: Prepare

Before any start can be made on engineering the system, some preparation is necessary.

Step 1.1 Select devices

We choose which field devices we wish to use in our automation task. This can be done by, for example, referring to the database on the server of PROFIBUS International.

Step 1.2 Collect GSD files

We bring together the General Station Description (GSD) files for our chosen field devices. This lets us know what properties the devices used have.

We will find these GSD files on a data medium supplied with the product or made available on the manufacturer's web server. PROFIBUS International also offers manufacturers the opportunity of directly storing their GSD files in the product catalogue. Unfortunately, this offer has only been taken up properly by a very small number of manufacturers.

Step 1.3 Load GSD files

The GSD files must be known to the planning tool. They are integrated into the device library of the planning tool. For this purpose, files are either copied to a special directory or explicitly read in with the planning tool.

Structure of GSD files

Every class 1 master and all field devices with slave functionality that conform to the standard must be described by the manufacturer by means of a GSD file. The GSD file is a master file containing device data.  GSD stands for 'general station description'.

Project planning tools for the PROFIBUS-DP master to be included in the project interpret the content of slave GSD files and generate from it a master parameter set for the class 1 master that will be in charge of payload traffic.

A class 1 master uses information from the GSD files of connected slaves to determine the expansion level of the bus, which services are supported by the slave in question, and the form in which data is exchanged.

GSD files are required for project planning and commissioning. Every manufacturer of a PROFIBUS-DP class 1 master provides a project planning tool for the class 1 master that knows the internal data structure of both the class 1 master and the host system. When making the project, the necessary GSD files must be made known to the project planning tool. This usually takes place when the GSD files are copied onto the PC's hard disk. (A precise path indication can be obtained from the description of the project planning tool). When planning a system project, the project planning tool interprets GSD file data for the chosen field device. Plausibility checks are also carried out at this early stage to ensure that project planning data has the correct logical construction.

A GSD file may be present either once, as when its construction is language-neutral (*.gsd) or several times, as when it has been written in a particular local language. In this case, a separate GSD file should be used for each language and they should only differ from each other in their visible-string type parameters. Language-related GSD files differ in the last letter of their extensions (*.gs?).

Default (language-neutral): ?=d

German ?=g

English ?=e

French ?=f

Italian ?=i

Portuguese ?=p

Spanish ?=s

The following rules apply for GSD-file names:

Abc_0008.gsd

signifying the following:

company identifier (here company Abc_), always 4 characters
Ident number 0008 assigned by the PNO , always 4 characters in hexadecimal
default. Language-neutral GSD(E) file

The properties of a devices are described with key words and values.

For historical reasons, there are different revisions of GSD syntax with an increasing number of key words. The latest version today is (2012) Version 5. The first key word therefore indicates the version of the GSD file:

Vendor_Name= "Company_ABC & Co"

Model_Name= "Modular I/O Station"

Revision= "Version 01"

The manufacturer's name, model name and revision of the device are limited to 32 characters as a visible string.

Revision_Number= 05

Version identifier for the DP device. The revision number here must match the revision number in the slave-specific diagnosis.

Ident_Number=0x00A2

The ident number identifies the type of DP device. Every field device is characterized by an ident number allocated to it by PROFIBUS International. It creates a unique reference to the GSD file and therefore to the technical data of that field device. Variants of field devices, which can be described with a GSD file, can use the same ident number (for example modular devices). It is only possible to exchange data with a field device if the DP master identifies the DP slave uniquely with the ident number during system start-up (parameter setting telegram).

An ident number may be ordered from PROFIBUS International. It is also possible to view here a list of currently used ident numbers.

Protocol_Ident= 0   ;PROFIBUS-DP device

Protocol used by DP device.

0: PROFIBUS-DP,

16 to 255: vendor-specific

Station_Type= 0   ;PROFIBUS-DP Slave

DP device type

0: DP slave,

1: DP master (class 1)

Further information about key words may be found in the appropriate chapters:

•Address changes for a DP slave

•Configuration  of a DP slave

•Setting the parameters of a DP slave

•Isochronous data cycle

•SYNC and FREEZE commands

•Alarm handling

A list of GSD key words mentioned in this manual may also be found in the index.

Step 2: Plan

Planning a PROFIBUS system takes place with a planning tool. This tool is generally made available by the controller manufacturer and is often closely coupled with programming the controller.

Difference between configuration and programming

Often, however, it is possible to differentiate clearly between controller program task and system configuration. Configuration teaches individual stations who should communicate and exchange data with whom. Programming defines what the controller does with this information. Parameter setting lays down the behaviour of field devices.

Step 2.1 Plan system