Funktionsbausteinen

Funktionsbausteine, or function blocks, are modular software components used in programmable logic controller (PLC) programming under the IEC 61131-3 standard. Each function block type defines a behavior with a defined set of input variables, output variables, and internal state. An instance of a function block type maintains its own data, enabling multiple independent blocks of the same type to operate concurrently within a program.

Function blocks differ from simple functions in that they can retain state across execution cycles. This memory allows them to model time-dependent or stateful behavior, such as timers or counters. A function (often represented as FC in IEC 61131-3) is typically stateless, while a function block (FB) can hold internal variables and perform ongoing processing.

Function blocks are assembled in PLC programs using languages supported by IEC 61131-3, including ladder diagram, function block diagram, and structured text. They are executed in program cycles and communicate through explicitly defined inputs and outputs. Many standard and vendor-provided blocks exist, such as timers (TON, TOF, TP), counters, latches, and arithmetic or logical blocks, which can be combined to build complex automation logic.

Applications and benefits include modularity, reusability, and easier maintenance. Function blocks support library creation, enabling domain-specific blocks to be shared across projects. They also facilitate abstraction and documentation of control logic. Challenges can include ensuring deterministic behavior, managing versioning and compatibility across platforms, and addressing differences in vendor implementations. Overall, function blocks are a fundamental concept in modern PLC programming, promoting scalable and maintainable automation solutions.