Fieldbus

The oldest commonly used field bus technology is Bitbus. Bitbus was created by Intel Corporation to enhance use of Multibus systems in industrial systems by separating slow i/o functions from faster memory access. In 1983, Intel created the 8044 Bitbus microcontroller by adding field bus firmware to its existing 8051 microcontroller. Bitbus uses EIA-485 at the physical layer, with two twisted pairs - one for data and the other for clocking and signals. Use of SDLC at the data link layer permits 250 nodes on one segment with a total distance of 13.2 km. Bitbus has one master node and multiple slaves, with slaves only responding to requests from the master. Bitbus does not define routing at the network layer. The 8044 permits only a relatively small data packet (13 bytes), but embeds an efficient set of RAC (remote access and control) tasks and the ability to develop custom RAC tasks. In 1990, the IEEE adopted Bitbus as the Microcontroller System Serial Control Bus (IEEE-1118).[2][3]

Today BITBUS is maintained by the BEUG - BITBUS European Users Group.[4]

Although fieldbus technology has been around since 1988, with the completion of the ISA S50.02 standard, the development of the international standard took many years. In 1999, the IEC SC65C/WG6 standards committee met to resolve difference in the draft IEC fieldbus standard. The result of this meeting was the initial form of the IEC 61158 standard with eight different protocol sets called "Types".

This form of standard was first developed for the European Common Market, concentrates less on commonality, and achieves its primary purpose—elimination of restraint of trade between nations. Issues of commonality are now left to the international consortia that support each of the fieldbus standard types. Almost as soon as it was approved, the IEC standards development work ceased and the committee was dissolved. A new IEC committee SC65C/MT-9 was formed to resolve the conflicts in form and substance within the more than 4000 pages of IEC 61158. The work on the above protocol types is substantially complete. New protocols, such as for safety fieldbuses or real-time Ethernet fieldbuses are being accepted into the definition of the international fieldbus standard during a typical 5-year maintenance cycle. In the 2008 version of the standard, the fieldbus types are reorganized into Communication Profile Families (CPFs).[5]

Both Foundation Fieldbus and Profibus technologies are now commonly implemented within the process control field, both for new developments and major refits.

In June 1999 the IEC's Committee of Action (CA) decided to take a new structure for the fieldbus standards beginning with a first edition valid at the January 1, 2000, in time for the new millenium: There is a large IEC 61158 standard, where all fieldbuses find their place.[6] The experts have decided that the structure of IEC 61158 is maintained according to different layers, divided into services and protocols. The individual fieldbuses are incorporated into this structure as different types.

The Standard IEC 61158 Industrial communication networks - Fieldbus specifications is split into the following parts:

• IEC 61158-1 Part 1: Overview and guidance for the IEC 61158 and IEC 61784 series
• IEC 61158-2 PhL: Part 2: Physical layer specification and service definition
• IEC 61158-3-x DLL: Part 3-x: Data-link layer service definition - Type x elements
• IEC 61158-4-x DLL: Part 4-x: Data-link layer protocol specification - Type x elements
• IEC 61158-5-x AL: Part 5-x: Application layer service definition - Type x elements
• IEC 61158-6-x AL: Part 6-x: Application layer protocol specification - Type x elements

Each part still contains several thousand pages. Therefore, these parts have been further subdivided into subparts. The individual protocols have simply been numbered with a type. Each protocol type thus has its own subpart if required.

In order to find the corresponding subpart of the individual parts of the IEC 61158 standard, one must know the corresponding protocol type for a specific family.

In the 2019 edition of IEC 61158 up to 26 different types of protocols are specified. In IEC 61158 standardization, the use of brand names is avoided and replaced by dry technical terms and abbreviations. For example, Ethernet is replaced by the technically correct CSMA/CD or a reference to the corresponding ISO standard 8802.3. This is also the case with fieldbus names, they all are replaced by type numbers. The reader will therefore never find a designation such as PROFIBUS or DeviceNet in the entire IEC 61158 fieldbus standard. In the section Compliance to IEC 61784 a complete reference table is provided.

It is clear that this collection of fieldbus standards in IEC 61158 is not suitable for implementation. It must be supplemented with instructions for use. These instructions show how and which parts of IEC 61158 can be assembled to a functioning system. This assembly instruction has been compiled subsequently as IEC 61784 fieldbus profiles.

According to IEC 61158-1[7] the Standard IEC 61784 is split in the following parts:

• IEC 61784-1 Profile sets for continuous and discrete manufacturing relative to fieldbus use in industrial control systems
• IEC 61784-2 Additional profiles for ISO/IEC 8802 3 based communication networks in real-time applications
• IEC 61784-3 Functional safety fieldbuses – General rules and profile definitions
• IEC 61784-3-n Functional safety fieldbuses – Additional specifications for CPF n
• IEC 61784-5-n Installation of fieldbuses - Installation profiles for CPF n

The IEC 61784 Part 1[8] standard with the name Profile sets for continuous and discrete manufacturing relative to fieldbus use in industrial control systems lists all fieldbuses which are proposed by the national standartization bodies. In the first edition in 2003 7 different Communication Profile Families (CPF) are introduced:

• CPF 1 FOUNDATION Fieldbus
• CPF 2 ControlNet
• CPF 3 PROFIBUS
• CPF 4 P-NET
• CPF 5 WorldFIP
• CPF 6 INTERBUS
• CPF 7 SwiftNet

Swiftnet, which is widely used in aircraft construction (Boeing), was included in the first edition of the standard. This later proves to be a mistake and in the 2007 edition 2 this protocol was removed from the standard. At the same time, the CPF 8 CC-Link, the CPF 9 HART protocol and CPF 16 SERCOS are added. In the edition 4 in 2014 the last fieldbus CPF 19 MECHATROLINK was included into the standard. The edition 5 in 2019 was just a maintenance revision without any new profile added.

See List of automation protocols for fieldbus which are not included in this standard.

Already in edition 2 of the fieldbus profile first profiles based on Ethernet as physical layer are included.[9] All this new developed Real-time Ethernet (RTE) protocols are compiled in IEC 61784 Part 2[10] as Additional profiles for ISO/IEC 8802 3 based communication networks in real-time applications. Here we find the solutions Ethernet/IP, three versions of PROFINET IO - the classes A, B, and C - and the solutions of P-NET,[11] Vnet/IP[12] TCnet,[13] EtherCAT, Ethernet POWERLINK, Ethernet for Plant Automation (EPA), and also the MODBUS with a new Real-Time Publish-Subscribe MODBUS-RTPS and the legacy profile MODBUS-TCP.

The SERCOS solution is interesting in this context. This network from the field of axis control had its own standard IEC 61491.[14] With the introduction of the Ethernet based solution SERCOS III, this standard has been taken apart and the communication part is integrated in IEC 61158/61784. The application part has been integrated together with other drive solutions into a special drive standard IEC 61800-7.

So the list of RTE for the first edition in 2007 is already long:

• CPF 2 CIP
• CPF 3 PROFIBUS & PROFINET
• CPF 4 P-NET[11]
• CPF 6 INTERBUS
• CPF 10 Vnet/IP[12]
• CPF 11 TCnet[13]
• CPF 12 EtherCAT
• CPF 13 ETHERNET Powerlink
• CPF 14 Ethernet for Plant Automation (EPA)
• CPF 15 MODBUS
• CPF 16 SERCOS

In 2010 already a second edition was published to include CPF 17 RAPIEnet and CPF 18 SafetyNET p. In the third edition in 2014 the Industrial Ethernet (IE) version of CC-Link was added. The two profile families CPF 20 ADS-net[15] and CPF 21 FL-net[16] are added to the edition four in 2019.

For details about these RTEs see the article on Industrial Ethernet.

For functional safety, different consortia have developed different protocols for safety applications up to Safety Integrity Level 3 (SIL) according to IEC 61508 or Performance Level "e" (PL) according to ISO 13849. What most solutions have in common is that they are based on a Black Channel and can therefore be transmitted via different fieldbuses and networks. Depending on the actual profile the safety protocol does provide measures like counters, CRCs, echo, timeout, unique sender and receiver IDs or cross check.

The first edition issued in 2007 of IEC 61784 Part 3[17] named Industrialcommunication networks – Profiles – Functional safety fieldbuses includes the Communication Profile Families (CPF):

• CPF 1 FOUNDATION Fieldbus[18]
• CPF 2 CIP with CIP safety
• CPF 3 PROFIBUS & PROFINET with PROFIsafe
• CPF 6 INTERBUS

SERCOS does use the CIP safety protocol as well.[19] In the second edition issued in 2010 additional CPF are added to the standard:

• CPF 8 CC-Link
• CPF 12 EtherCAT with Safety over EtherCAT
• CPF 13 Ethernet POWERLINK with openSAFETY
• CPF 14 EPA

In the third edition in 2016 the last safety profile CPF 17 SafetyNET p was added. A new edition 4 is expected to be published in 2021. The standard has now 9 different safety profiles. They are all included and referenced in the global compliance table in the next section.

The protocol families of each brand name are called Communication Profile Family and are abbreviated as CPF with a number. Each protocol family can now define fieldbuses, real-time Ethernet solutions, installation rules and protocols for functional safety. These possible profile families are laid down in IEC 61784 and compiled in the following table.

As an example, we will search for the standards for PROFIBUS-DP. This belongs to the CPF 3 family and has the profile CP 3/1. In Table 5 we find that its protocol scope is defined in IEC 61784 Part 1. It uses protocol type 3, so the documents IEC 61158-3-3, 61158-4-3, 61158-5-3 and 61158-6-3 are required for the protocol definitions. The physical interface is defined in the common 61158-2 under type 3. The installation regulations can be found in IEC 61784-5-3 in Appendix A. It can be combined with the FSCP3/1 as PROFIsafe, which is defined in the IEC 61784-3-3 standard.

To avoid the manufacturer having to list all these standards explicitly, the reference to the profile is specified in the standard. In the case of our example for the PROFIBUS-DP, the specification of the relevant standards would therefore have to be

Compliance to IEC 61784-1 Ed.3:2019 CPF 3/1

Requirements of fieldbus networks for process automation applications (flowmeters, pressure transmitters, and other measurement devices and control valves in industries such as hydrocarbon processing and power generation) are different from the requirements of fieldbus networks found in discrete manufacturing applications such as automotive manufacturing, where large numbers of discrete sensors are used including motion sensors, position sensors, and so on. Discrete fieldbus networks are often referred to as "device networks".

Already in the year 2000 the International Electrotechnical Commission (IEC) decided that a set of controller-device interfaces (CDIs) will be spezified by the Technical Commitee TC 121 Low-voltage switchgear and controlgear to cover the device networks. This set of standards with the number IEC 62026[20] includes in the actual edition of 2019 the following parts:

• IEC 62026-1: Part 1: General rules
• IEC 62026-2: Part 2: Actuator sensor interface (AS-i)
• IEC 62026-3: Part 3: DeviceNet
• IEC 62026-7: Part 7: CompoNet

The following parts have been withdrawn in 2006 and are not maintained anymore:

• IEC 62026-5: Part 5: Smart distributed system (SDS)
• IEC 62026-6: Part 6: Seriplex (Serial Multiplexed Control Bus)