The event driven execution model allows an explicit specification of the execution order of function blocks. IEC enables an application-centric design, in which one or more applications, defined by networks of interconnected function blocks, are created for the whole system and subsequently distributed to the available devices. All devices within a system are described within a device model. The topology of the system is reflected by the system model.
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The Standard The IEC Standard defines an open architecture for the next generation of distributed control and automation. This architecture represents a light-weight component solution that provides essential features such as encapsulation of semantics from a particular platform, portability, reconfiguration and a holistic view on distributed applications.
As the standard is designed for the development of distributed systems, it further supports features like reusability and interoperability. The IEC Standard provides a generic model for distributed systems. This model includes processes and communication networks as an environment for embedded devices, resources and applications.
Applications are built by networks of Function Blocks. There are two types of Function Blocks. Thus, Composite Function Blocks enable modular design methodologies. ECC , which are similar to state machines. The elements of the ECC are states and event-triggered transitions.
An ECC can trigger the execution of Algorithms by the occurrence of events. An executed algorithm produces new output data from the input data. When the algorithm has finished, an output event is generated. But Output events can also be emitted without the execution of algorithms.
Output events might be the input events for other Function Blocks.
It has inputs and outputs for controlling various systems. In general, buttons and sensors generate the inputs, while the outputs control motors. A PLC is however specifically prepared for use in industry. The PLC is programmed according to the required application.
IEC 61499 101