Profile contract

fbd.basic@1

IEC 61131-3 FBD: function blocks (rect with name/type header and typed pins), typed wire connections (BOOL/INT/DINT/REAL/TIME/STRING/WORD), negation bubbles on BOOL pins, feedback loops allowed. Ladder (LD) hosting follows in a later item.

graph projectionIEC 61131-3 function block diagram

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Primary palette

fbd.blockfbd.variable

Relationship roles

fbd.wire

Legal endpoints

Relation	Source roles	Target roles	Self relation
`fbd.wire`	fbd.block, fbd.variable	fbd.block, fbd.variable	Not allowed

Profile verification

Pins declare BOOL/INT/DINT/REAL/TIME/STRING/WORD; wire endpoint types match.
Negation is allowed only on BOOL pins. Feedback cycles are legal and do not trigger a generic DAG rule.

Profile defaults

Explicit file settings override eligible CSS, then these profile defaults and the common standard apply. Unspecified semantic facts remain unspecified.

{
  "projection.kind": "graph",
  "projection.profile": "fbd.basic@1"
}

Projection properties

kind, profile, inputs, analysis_budget, traces, iso, depth

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Design operations

Create block/variable; add typed pins; connect wire; toggle BOOL negation; inspect mismatches.

Bounded analysis

Structural verification and display only; no execution or implied process engine.

Outside this profile

PLC execution/compilation
IEC interchange (XML) formats
formal IEC certification