FOUNDATION Fieldbus Technology Explained


Fieldbus is a bidirectional communication protocol that provides real-time, closed-loop control between intelligent field instruments and host systems. A host can be any software application: from a technician's handheld device or laptop, to a plant's process control, asset management, or safety system. Being a peer-to-peer system, communication can occur directly between two fieldbus-enabled field devices or between field devices and a control or asset management system. Given the all-digital nature of fieldbus, following industry guidelines on proper wiring and termination practices ensures reliable communication.

Roughly 90% of issues with digital communication are caused by physical layer installation mistakes. The good news is installing fieldbus is no harder than traditional systems!


Unlike other digital architectures, FOUNDATION Fieldbus was designed from the ground up to enable control-in-the-field (CIF) strategies across the plant. This means that during a host system failure, field instruments can communicate directly with one another to maintain continued safe operations. The technology includes a number of physical layers (the medium that the signal communicates through) and a rich software platform that allows for the over 1,000 registered products to interoperate between various manufacturers of devices and control systems — offering end users the flexibility to choose best-in-class solutions for their application.

FOUNDATION Fieldbus also supports the NAMUR NE107 recommendations for managing data from intelligent instrumentation. This ensures diagnostic data is managed effectively, and you only see the information you need to see, when you need it.

The FieldComm Group owns the FOUNDATION Fieldbus specifications and provides specification development, training, and product registration services associated with the technology.


Fieldbus provides significant benefits for all types of industrial operations:

  • Control-in-the-field (device to device communication)
  • Closed-loop control (sensor feedback)
  • Reduced cabling (multiple devices per cable)
  • Reduced hardware (via VirtualMarshalling™)
  • Reduced system footprint (fewer I/O cards, devices, cable tray, etc.)
  • Reduced device count (multivariable devices)
  • Faster commissioning (compared to traditional approaches)
  • Tighter control constraints (via control in the field)
  • Enhanced diagnostics (via higher power availability and signal status)
  • Easy online upgrades (bumpless transfer allows upgrades from the comfort of your work console)


    FOUNDATION™ Fieldbus H1 technology is designed specifically for field-level interface and device integration within the process plant environment. It is the foundation upon which Information-driven systems offering increased connectivity, real-time data, and advanced analytics can deliver better performance and enhance competitive advantages—not only in the plant, but across the enterprise and out to its value chain.

    FOUNDATION Fieldbus H1 is an interoperable, bi-directional, digital, serial, publisher-subscriber communications network, which is suitable for use in hazardous and potentially explosive areas (Ex zones 0 and 1), as well as intrinsic safety (IS) applications. Each H1 segment supports a length of 1,900 meters and connects up to 32 field devices, depending on the individual environment. These limits can be extended using bridges.

    There are several possible network topologies in FOUNDATION H1, such as point-to-point, bus with spurs, daisy chain, tree or mixed (a combination of all supported topologies). The trunk is the main communication pathway between devices and is typically the power supply for spurs on the segment.

    The H1 solution enables field instruments and other devices to execute control functions, thus reducing the load on plant computers and workstations. Since the H1 network is digital, I/O conversion subsystems are eliminated.

    The FieldComm Group tests and registers FOUNDATION Fieldbus (H1 & HSE) devices to ensure interoperability of registered products from multiple vendors. This enables the end user to select the best instruments for the application regardless of the host system supplier.


      Today, some automation projects are adopting various alternatives to traditional I/O and marshalling technology. But why make physical marshalling easier, when you can eliminate it entirely? The advantages of software-based distributed I/O connectivity inherent to FOUNDATION Fieldbus are numerous. The following are a few:

      • Reduce cabling
      • Reduce system footprint
      • Simplified marshalling
      • Fewer points of failure
      • Fewer physical layer connection points (the cause of roughly 90% of instrumentation errors)
      • No I/O mismatching
      • Simplify device additions

      Many of the functions provided by hardware in a conventional control system are no longer required by a FOUNDATION Fieldbus system, or are handled through software instead.


      FOUNDATION Fieldbus technology was developed from the ground up as a way to eliminate traditional marshalling all together through VirtualMarshalling™ connectivity solutions. In other words, VirtualMarshalling enables software-based distributed I/O connectivity in which devices provide multiple signals over the same two terminals. Instead of relying on custom hardware configurations to accomplish the functions of traditional marshalling, FOUNDATION Fieldbus accomplishes these tasks through a software-based structure. All signal linking (block to block) is done in software without hardwiring — even better the devices themselves self declare the type of I/O they can operate as. This approach allows late addition of feedback and auxiliary measurement and control signals without the need for additional wiring, as well as change of devices without switching I/O cards. Burnt shunt resistors are also eliminated. More devices can be added without laying more cable.

      With security concerns an ever present thought on the industries minds, VirtualMarshalling adds yet another critically important element. It allows companies to segregate the enterprise layer systems from the field layer systems by not bringing the control and/or enterprise layer subsystem out into the field where the device connection points are brought in. Most users cringe at the thought of field service engineers with access to the control network backbone.

      A unique characteristic of the FOUNDATION Fieldbus architecture — ensuring device interoperability — is its use of a fully specified, standard User Layer based on "Blocks" and Device Descriptions (DDs). The User Layer defines a Function Block Application Process (FBAP) using Resource Blocks, Function Blocks, Transducer Blocks, System Management, Network Management and DD technology. Resource Blocks define parameters that pertain to the entire application process (e.g., manufacturing ID, device type, etc.). Function Blocks encapsulate control functions (e.g., PID controller, analog input, etc.) and Transducer Blocks offer an interface to sensors such as temperature, pressure and flow, and actuators for valves.

      By utilizing this unique feature, FOUNDATION Fieldbus can ensure interoperability at the Field Layer while allowing host systems access to advanced digital intelligence provided by the field instrument regardless of manufacturer. Additionally, Function Blocks allow devices to communicate directly thus enabling Control in the Field (CiF) which negates or minimizes the effects of any loss or failure of supervisory control. Furthermore, each block contains parameters that provide a value and a status with each signal therefore allowing the system to intelligently determine whether the measurement an operator is seeing is good, bad or uncertain. This intelligence is what provides a strong basis for the Industrial Internet of Things (IIoT) and Industrie 4.0 which are all about making systems smarter so that people can make more informed business decisions.

      The FOUNDATION Fieldbus protocol is designed to be compatible with the specifications of the International Electrotechnical Committee (IEC). FOUNDATION H1 and HSE specifications are included in the IEC 61158 international standard. The FOUNDATION specifications are also compliant with IEC 61804 (Function Blocks for Process Control and Electronic Device Description Language) and IEC 61508 (Functional Safety of Electrical/Electronic/ Programmable Electronic Safety-related Systems).

      The FOUNDATION Technical Specifications are based on the OSI (Open Systems Interconnection) layered communications model, and consists of three major functional components:

      1. Physical Layer
      2. Communication "stack" Layer
      3. User Layer


      The Physical Layer corresponds to OSI Layer 1, which receives encoded messages from the upper layers and converts the messages to physical signals on the fieldbus transmission medium and vice-versa.


      The Communication Layer (a.k.a. "stack") corresponds to Layers 2 and 7 in the OSI model.

      • Layer 2, the Data Link Layer (DLL), controls transmission of messages onto the fieldbus through Layer 1. The DLL also manages access to the fieldbus through a deterministic, centralized bus scheduler called the Link Active Scheduler (LAS). The LAS is used for scheduling transmissions of deterministic messages and authorizing the exchange of data between devices.
      • Layer 7, the Application Layer (AL), encodes and decodes User Layer commands.


      One of the most important layers in the FOUNDATION Fieldbus model is the User Layer. This layer was added to the OSI model because of user demand — pure and simple. The User Layer enables peer to peer communication between devices and systems and is the basis upon which the function block models are built. Function blocks enable important aspects of FOUNDATION Fieldbus to operate such as Control in the Field (CiF), Advanced Diagnostics, Alert and Alarms, Status and the ever important Analog I/O and Digital I/Os along with a host of other advanced feature capabilities.

      Standards Model

      FOUNDATION Fieldbus technology is more than just a network — it’s a forward-looking digital automation infrastructure that is built on field-proven IIoT concepts to manage data, communication, field assets, and plant events while providing highly distributed control functionality and interoperability between devices and subsystems. This real-time communication system has been designed specifically for process control applications in order to enable a smart network infrastructure that provides visibility at all levels within an organization — from plant floor to enterprise.

      Field Level systems (H1 devices and associated Function Blocks) work in unison with the high speed Integration Level systems to provide a complete open-standard automation infrastructure.

      The Integration Level includes:


        A host profile defines a minimum set of FOUNDATION-specific features that must be implemented by a host to achieve compliance to a specific host class. A host may incorporate one or more hardware and software components as defined by the host manufacturer. Currently, FieldComm Group defines five profile classes. Each of these host classes has its own set of characteristics, primary end users, and use cases.

        These include:

        1. Class 61 – Integrated Host: Primary, on-process host that manages the communication and application configuration of all devices on a network
        2. Class 62 – Visitor Host: Temporary, on-process host with limited access to device parameterization
        3. Class 63 – Bench Host: Primary, off-process host for configuration and setup of a non-commissioned device
        4. Class 64 – Bench Host: Primary, off-process host with limited access to device parameterization of an off-line, commissioned device
        5. Class 71 - SIF Integrated Host: Primary on-process host for Safety Instrumented Functions


        In addition to the various host classifications, each classification also has its own set of Mandatory, Optional, or Prohibited features. View the Host Features Table below for a full breakdown of Mandatory, Optional and Prohibited features of each host classification.


        EDDL and FDI (Field Device Integration) are the building blocks of today's and tomorrow's modern process control systems.


        Electronic Device Description Language (EDDL) is a programming language used to create Device Descriptions (DDs) to describe the attributes of field devices in an Operating System (OS). It is a universal, proven and state-of-the-art method of accessing diagnostic, real-time and asset management information contained in more than 30 million compliant field instruments from a host of manufacturers, and to provide optimum data and device interoperability. DDs provide device functions such as generic digital and analog input/output modules, HMI displays and transmitters, on-off and regulating valves, and closed-loop controller diagnostics.

        With EDDL technology, a user can calibrate instruments, diagnose problems, provide data for user interface displays, identify process alarms and obtain information needed for high-level software, such as MES, UI/SCADA, plant historians, asset management and ERP.

        To learn more about EDDL technology, download the brochure.




        FDI, put simply, is the rationalization of benefits of EDDL and FDT/DTM technologies. Users requested a uniform device integration solution for process industries that combines the broad benefits of EDDL with the enhanced feature sets of FDI. This solution must also span across all host systems and devices regardless of manufacturer. Thus, FDI was born. FDI device packages make it easier for automation suppliers to develop and integrate intelligent devices, because suppliers only need to create a single, unified package for each intelligent device that can work with all host systems and tools. This reduces overall development costs, while preserving and expanding existing functionality. Users will also find it easier to manage information from intelligent devices with a single device package, instead of juggling different technologies and investing significant capital in custom integration efforts to connect multiple technology platforms.        

        To learn more about FDI technology, please visit FDI Technology Overview.


        FOUNDATION Fieldbus High Speed Ethernet (HSE) enables tight integration and a free exchange of information needed for the plant enterprise. HSE is a superior solution to proprietary, Ethernet-based technologies since it provides end users with interoperability between disparate controllers and gateways in the same way that H1 supports interoperability between transmitters and actuators from different suppliers. And like H1, HSE is an international standard (IEC 61158).

        HSE functions as a control network technology specifically designed for process automation to connect higher-level devices such as controllers and remote-I/O, high-density data generators, etc., and for horizontal integration of subsystems.

        FOUNDATION HSE is ideally suited for use as a control backbone with capabilities for device, subsystem and enterprise integration. The HSE implementation employs a transfer rate of 100 Mbit/s and can be used for connecting hosts like Distributed Control Systems (DCSs) and linking devices via standard Ethernet cabling including fiber optic. It employs a full-fledged redundancy scheme giving control systems greater availability than systems using simple ring-topology. Use of unmodified Ethernet and standard IP makes HSE systems more cost-effective than other Ethernet solutions and proprietary networks. Since HSE is a standard, it enables simple and tight integration between package units and the main control system. The HSE network is easier and cheaper to manage based on common network knowledge and standard SNMP tools.

        Additional Resources

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