Allen-Bradley PLC-5/20 processor module - 1785-L20BC

A sourced PLC-5 processor record with an inferred chassis and I/O position and explicit installation unknowns.

Documented identity

Rebuilt from individual evidence

System position

Unknown: evidence limits

The source identifies this exact reference as an Allen-Bradley PLC-5/20 processor module.

Inferred system position: it executes control logic between the PLC-5 chassis and connected I/O.

Unknown: chassis, program, firmware, I/O wiring, condition, and compatibility.

Exact reference: 1785-L20BC
Category: PLC / CPU
Evidence checked: 2026-09-11

System role

This section explains what the product does and where it acts in the surrounding system.

Function: The PLC-5 processor executes control logic and exchanges data with connected I/O.
System position: Inferred system position: the processor sits in the PLC-5 chassis between the control program and local or remote I/O.
Upstream / inputs: Field I/O data and controller messages enter the processor.
Downstream / outputs: The processor updates I/O commands and controller messages for the controlled system.
Limitations: Unknown: chassis, program, firmware, I/O wiring, condition, and compatibility.

Evidence ledger

Facts, inferences, and unknowns are kept separate.

Facts

The exact-reference listing identifies 1785-L20BC as an Allen-Bradley PLC-5/20 processor module.
Confidence: high
- www.plcproducts.com — retrieved 2026-09-11; high confidence

Inferences

Inferred system position: the processor sits in a PLC-5 chassis between the control program and local or remote I/O.
Confidence: high
Rationale: The exact listing identifies a PLC-5 processor, while Rockwell PLC-5 documentation describes processor interaction with I/O and controller software.
- www.plcproducts.com — retrieved 2026-09-11; high confidence

Unknowns

Unknown: chassis, program, firmware, I/O wiring, condition, and compatibility.
Confidence: low
Missing evidence: No installation-specific record was found.

System position diagram

Field data enters the PLC-5 processor and leaves as local or remote I/O commands. — Inferred PLC-5 control path through the processor and I/O.

View Mermaid source

flowchart LR; input[Input data] --> processor[PLC processor]; processor --> io[I/O commands]

View diagram labels

Nodes: Field and network input; PLC-5 processor; Local or remote I/O
Edges: Processor executes control logic

Next action

Evidence supports a conservative PLC processor record; verify project and chassis details before use.

Unknown: verify chassis, program, firmware, I/O wiring, condition, and compatibility before installation.

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