Glossary · Distributed automation and IEC 61499
Data input (IEC 61499)
Also known as: Data input variable
German: Dateneingang
In IEC 61499, a data input is an input of a function block interface that receives a typed data value; the value is sampled into the function block when an event input associated with it through a WITH qualifier occurs.
- IEC 61499
- Standards
In one sentence
An IEC 61499 data input receives a typed value, sampled into the function block when its associated event input occurs.
Example
The data input SETPOINT of a temperature block is read only when the event input REQ arrives, not every time the connected value changes.
How it applies
- Engineering: Data inputs carry values such as setpoints, measurements or parameters. They use IEC 61131-3 data types. Their values are sampled only with an associated event, which gives consistent snapshots and avoids reading half-updated values.
- Design: Every data input that the block needs should be associated with the events that use it. A data input without an association may never be sampled; tools typically warn about this.
- Testing: Tests should verify that changes of a data input take effect only after the associated event.
- Documentation: In the block's interface table, list each data input with type, unit, meaning and the events it is associated with.
IEC 61499 data input vs. IEC 61131-3 input variable
An Input variable in IEC 61131-3 is read whenever the block is called in the cycle. An IEC 61499 data input is read only when an associated Event input occurs. The event, not the cycle, drives the sampling.