Allen-Bradley / Rockwell · PLC-5 · Platform migration guide
Migrating from PLC-5 to ControlLogix: what replaces it and what changes
The Allen-Bradley PLC-5 platform is discontinued — Rockwell retired the remaining processors in 2017 — and the documented direction is migration to the ControlLogix 1756 platform, with 5580-class controllers preferred in current migration material. This is a platform migration, not a drop-in swap: there is no catalog-number replacement for a PLC-5 processor. The pages below analyze individual obsolete PLC-5 parts, each with source-backed evidence for its migration path.
What changes in a PLC-5 to ControlLogix migration
| Controller and chassis | The PLC-5 chassis, power supply, and processor leave for a ControlLogix chassis with a 1756 controller. Size the new controller from the program and I/O count, not from the old catalog number. |
|---|---|
| I/O | 1771 I/O gives way to 1756 I/O. Where a full rewire cannot be scheduled, 1492 wiring-conversion hardware carries existing field wiring across; confirm the terminal layout when ordering. |
| Communications | DH+, remote I/O, and ControlNet networks move to EtherNet/IP. Map every scanner, adapter, and message path before the cutover. |
| Software | RSLogix 5 programs convert to Studio 5000 Logix Designer with the OEM conversion tools. Converted logic needs review rung by rung — conversion output is a starting point, not a finished program. |
| Wiring and integration | Keep existing field wiring where conversion hardware supports it and re-terminate the rest. Re-address devices and rework the network cabling as part of the move. |
PLC-5 parts analyzed on EquipVector
| Allen-Bradley 1785-L80B | PLC-5/80 processor → ControlLogix 1756 platform migration, with conversion tooling; remanufactured units can cover the changeover. |
|---|---|
| Allen-Bradley 1785-L60B | PLC-5/60 processor → ControlLogix 1756 platform migration, with conversion tooling; remanufactured units can cover the changeover. |
| Allen-Bradley 1785-L40B | PLC-5/40 processor (48K memory class) → ControlLogix 1756 platform migration planned around program size and I/O/network configuration. |
| Allen-Bradley 1771-IBD | PLC-5 input module → no exact module swap verified; stay running on refurbished stock while planning the ControlLogix conversion. |
Note: a reseller memory-match table maps specific PLC-5 processors to specific ControlLogix controllers, but it has no OEM basis — size the controller to the application, as the 1785-L40B analysis documents.
How to scope the migration
The exact path depends on your installation, not just the part number. Before requesting a review, gather:
- Program size and memory class (e.g. 48K on a PLC-5/40), plus I/O count by module.
- Network map: DH+ segments, remote I/O racks, scanners, adapters, and message paths.
- Chassis, power, and panel constraints that decide what the new 1756 chassis must fit.
- Whether failed or working units are involved — the OEM migration program takes working PLC-5 controllers back for remanufacture, which can bridge a staged cutover; failed units do not qualify.
Planning a PLC-5 migration?
Request a migration review and we'll help confirm the ControlLogix path, the conversion hardware, and what changes in your installation.
Request a migration reviewRelated migration analysis
- Allen-Bradley / Rockwell 1756-L61 — Migration destination: ControlLogix platform. Note the L61 itself is discontinued, with its own path to the 1756-L71 or 5580.