IEC 61499
A Standard for Software Reuse
in Embedded, Distributed Control Systems

Author: James H. Christensen
with contributions from Alois Zoitl

All or part of the content of this document may be used under the terms of the Creative Commons Attribution 3.0 License, provided that attribution is made by including the URL http://www.holobloc.com/papers/iec61499/overview.htm in the reused content.

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:

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: 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:

Example 1: Processing a Message

In the example shown below:
  1. A message arrives from another resource (possibly in a remote device) via the communication interface.
  2. 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.
  3. 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.
  4. The resource then issues an event from the basic FB, which is propagated to an event input of the I/O SIFB.
  5. 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

In the example shown below:
  1. Something happens at an input interface (a user turns a knob, a limit switch senses the presence of a package on a conveyor, etc)., which causes the resource to map the input data to an output of the I/O SIFB.
  2. The resource maps the input data into a data output of the I/O SIFB, which in this case is wired to the data input of a communication SIFB. The resource then issues an event from the I/O SIFB, which is propagated to an event input of the communication SIFB.
  3. The arrival of this event at the communication SIFB causes a message containing the input data to be sent to a resource somewhere else in the system.

Configuration

IEC 61499-compliant software tools can be used according to the following procedure to configure distributed control and automation systems from libraries of reusable IEC 61499-compliant components:
  1. Configure the devices in the system: their names, types, parameters, and network interconnections.
  2. Configure the name, type and parameters of each resource in the devices.
  3. Build the required application functionality in each resource by adding and interconnecting function blocks from a library of function block types and setting their parameters as necessary.
  4. Add the communication service interface function blocks (SIFBS) necessary for proper transmission of data and synchronization of operations among resources, set their parameters and interconnect them as needed with the application function blocks.

Software Tools

Following is a list of IEC 61499-related software tools known to the author. Such tools should meet the requirements defined in IEC 61499-2, and should also have their characteristics defined in a Compliance Profile as specified in IEC 61499-4.

Books

Links


Last updated: 2014-10-19.
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