Field Level

Field Level


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.


Please visit our YouTube channel for more videos on FOUNDATION Fieldbus as well as FDI and HART technologies.


    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


    The FOUNDATION Fieldbus Technical Specifications is a complete, bookmarked, word-searchable software package that includes the latest FOUNDATION Fieldbus H1, High Speed Ethernet (HSE) and Physical Layer technical specifications.


    FOUNDATION Fieldbus technology is more than just a network — it’s a forward-looking digital automation...