IEC 61499

Authors

James Christensen

Contributors

Alois Zoitl

What is IEC 61499?

IEC 61499-1 defines an open architecture for distributed and embedded control and automation. In conjunction with an appropriate compliance profile as defined in IEC 61499-4 and software tools meeting the requirements of IEC 61499-2, reusable software modules (function blocks) can be developed and deployed in distributed systems that will meet the requirements of:

portability: Software tools can accept and correctly interpret software components and system configurations produced by other software tools.
interoperability: Embedded devices can operate together to perform the functions needed for distributed applications.
configurability: Any device and its software components can be configured by software tools from multiple vendors.

Encapsulation

Function Block Types

In the IEC 61499 standard, the basic unit for encapsulating and reusing Intellectual Property (IP="know-how") is the function block type. In object-oriented terms, this is a class defining the behavior of (possibly) multiple instances. It includes event inputs and outputs as well as the more traditional data inputs and outputs, to provide for synchronization between data transfer and program execution in distributed systems.

Basic Function Blocks

As its name implies, the basic function block type is the "atom" out of which higher-level "molecules" are constructed. With IEC 61499 compliant software tools, software developers can encapsulate IP in the form of algorithms written in Java or the IEC 61131-3 programming languages. Execution of these algorithms is triggered by Execution Control Charts (ECCs), which are event-driven state machines similar to the well-known Harel Statecharts.

Service Interface Function Blocks

Another "atomic" function block type is the service interface function block (SIFB) type. This represents the interface to low-level services provided by the operating system or hardware of the embedded device, such as:

Graphical User Interface (GUI) elements such as a slider (illustrated below), knob or pilot light
Communication services (the CLIENT_2 SIFB illustrated below is a communication "client" for a remote "server")
Interfaces to hardware such as a temperature sensor, a motor speed controller, a control valve or a room light intensity controller.

IEC 61499-compliant software tools and and their associated runtime packages provide a large selection of GUI and communications SIFBs. Providers of hardware SIFBs (typically the manufacturers of embedded devices) can use IEC 61499-compliant software tools to document how they work in the form of service sequence diagrams.

Reuse

Software developers can use IEC 61499-compliant software tools to build higher-level function block "molecules" called composite function block types out of lower-level function block "atoms" (component function blocks). This is done by specifying the event and data interfaces of the composite type, then filling it with a diagram showing how its internal component function blocks are connected. In this kind of function block, execution of the algorithms in the component function blocks is controlled by the flow of events from one component to another.

Distribution

In the IEC 61499-1 architectural model, distributable applications are built by interconnecting instances of reusable function block types with appropriate event and data connections,in the same manner as designing a circuit board with integrated circuits. Using IEC 61499-compliant software tools, these function blocks can then be distributed to physical devices across a network, as long as these devices comply with the applicable compliance profile.

It is also possible to distribute an application across multiple resources within a device. Resources might be multiple processors plugged into a backplane, or multiple tasks within a single processor with a multitasking operating system. In the example shown below, pieces of Application A run in Resources x, y and z, as well as other devices in the system; pieces of Application B run in resource z and in other devices; and Application C runs "locally" in Resources x and y.

Integration

In the IEC 61499 architecture, resources are the workhorses that provide the services needed to integrate all the pieces of applications into a working distributed system. IEC 61499-compliant software tools can be used to:

Map the messages that are passed back and forth between devices into the input and output events and data of communication service interface function blocks (SIFBs).
Use event and data inputs and outputs to trigger the performance of the algorithms of basic and composite function blocks, and synchronize their operation with other function blocks
Map the data and event inputs and outputs of I/O SIFBs to the inputs and outputs of the system, where it can sense what is going on in the physical world and take appropriate physical actions in response.

Example 1: Processing a message

In the example shown below:

A message arrives from another resource (possibly in a remote device) via the communication interface.
The resource maps the data in the message into a data output of the communication SIFB, which is wired to the data input of a basic function block; the resource then issues an event from the SIFB, which is propagated to an event input of the basic FB.
The arrival of this event causes the resource to execute the basic FB's algorithm, which uses the value of the data input to produce new values for the data outputs, which are wired to an I/O SIFB.
The resource then issues an event from the basic FB, which is propagated to an event input of the I/O SIFB.
The arrival of this event at the SIFB causes the resource to perform an appropriate action (start or stop a motor, set a room light level, etc.), based on the data input values of the SIFB.

Example 2: Processing an Input Event