Glossary · Distributed automation and IEC 61499
Basic function block
Also known as: Basic FB, BFB
German: Basisfunktionsbaustein
In IEC 61499, a basic function block is a function block type whose behavior is defined by an execution control chart (ECC) that reacts to input events by executing algorithms and issuing output events, with internal variables that persist between invocations.
- IEC 61499
- Standards
In one sentence
An IEC 61499 basic function block defines its behavior with an execution control chart that runs algorithms in response to events.
Example
A basic function block for a valve has the input events OPEN and CLOSE; its ECC runs the matching algorithm and fires the output event CNF when done.
How it applies
- Engineering: Basic function blocks are the atomic building blocks of IEC 61499 applications. Their interface has event inputs and outputs, data inputs and outputs; inside are an Execution control chart (ECC), algorithms (often in structured text) and internal variables.
- Behavior: Nothing happens without an event. An incoming event makes the ECC evaluate its transitions; active states run algorithms and emit output events. This event-driven model differs from the cyclic execution of IEC 61131-3.
- Testing: Each basic function block can be tested in isolation by feeding event sequences and checking outputs and output events.
- Documentation: Document each block type with its interface table (events, data, WITH associations), ECC diagram and algorithm descriptions. That reference information is reused wherever the type is instantiated.
Basic vs. composite function block
A basic function block contains an ECC and algorithms. A Composite function block contains a network of other function blocks and no ECC of its own.