Processes, interactions and lifecycle
IEC 61131-3 ladder diagram / relay logic
Three rungs between the power rails: normally-open and normally-closed contacts driving coils, one coil per rung, a parallel OR branch, and a hosted function block.
ladder.basic@1New DDN source
Why use it?
Ladder logic is the control-room reading of combinatorial logic: conditions left-to-right, one output per rung.
When it helps
Industrial control documentation where electricians and engineers share one reading of the wiring.
How to read it
- Power flows conceptually left rail to right rail.
- Contacts in series are AND; contacts stacked on parallel tracks are OR.
- One rung drives exactly one coil — the validator enforces it.
What you need
- The signals (contacts)
- The outputs (coils and their modes)
- Rung order
Things to check
- A rung with two coils is an error, not a design.
- Branches come from the wiring topology — you do not declare them.
Scope of this diagram
Common-practice ladder rendering and validation; no PLC compilation, execution or IEC XML interchange.
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.