Standards families
IEC 61131-3 function block diagram
Function blocks wired input-to-output: typed pins, feedback paths, the dataflow reading of control logic.
fbd.basic@1New DDN source
Why use it?
Control engineers read dataflow, not ladder rails; the FBD is the same logic drawn as a circuit of blocks.
When it helps
Process-control documentation, interlock logic, any block-and-wire control review.
How to read it
- Blocks compute; pins are typed inputs and outputs; wires carry values left to right except feedback.
- Read feedback loops deliberately — they are state, and reviewers must find them.
What you need
- The blocks and their types
- The pin connections
- The feedback paths
Things to check
- Do not wire an output to an output.
- A feedback loop without a memory block is an algebraic loop — say where the state lives.
Scope of this diagram
Declared FBD with pin-type validation; no PLC compilation or scan-cycle simulation is performed.
Work with the converted example
- Open the viewer and select
d. Inspect the rendered view and its source. - Open the designer. Keep the selected profile and inspect its legal palette and property controls.
- Change one displayed title or an appropriate data value. Apply the edit and check the resulting diagram.
- Run the verifier and review its diagnostics before moving complete content into review.
- Download your edited DDN source to retain the change.
The example uses the indentation-based ddn-next-1 dialect. The language guide explains reusable definitions, dotted data rows and explicit property blocks.