Allen-Bradley / Rockwell · PLC CPU · PLC-5/40 processor (48K memory)
Allen-Bradley / Rockwell 1785-L40B
Analysis reviewed: September 12, 2026
What should replace this part?
The documented replacement is ControlLogix 1756 platform. This is a platform migration, not a drop-in swap.
Plan the ControlLogix migration around the 48K program size and the existing I/O/network configuration — no catalog swap exists
- The PLC-5 platform is discontinued, and the OEM migration program points it at the ControlLogix 1756 platform.
- The program funds the move with conversion tooling, wiring-conversion hardware discounts, and a remanufacturing bridge for working units.
- The 48K program size informs application sizing, but controller selection depends on the actual application and configuration. A reseller memory-match table exists but has no OEM basis, so it informs nothing.
Your options
What will need to change?
| Hardware | The PLC-5 chassis, power supply, and 1771 I/O leave for a ControlLogix chassis with 1756 I/O, using the 1492 wiring-conversion system where a rewire cannot be scheduled. |
|---|---|
| Software | RSLogix 5 programs convert to Studio 5000 with the OEM conversion tools. Converted logic needs review rung by rung — conversion output is a starting point, not a finished program. |
| Communications | DH+ and remote I/O networks give way to EtherNet/IP. Map every scanner, adapter, and message path before the cutover weekend. |
| I/O | The 1771 I/O gives way to ControlLogix I/O through the program's wiring-conversion hardware. Keep the existing field wiring where the conversion hardware supports it and re-terminate the rest. |
For anything not listed here, check the replacement manual against your existing configuration.
Need help confirming this replacement?
Send us the part number and current setup for 1785-L40B. We'll help determine whether you need a replacement, repair, original-stock sourcing, or a migration.
Request a replacement reviewCan I still buy the original?
Lifecycle
Status: Discontinued
Reported date: 2017-06 (Reported by secondary sources; exact manufacturer confirmation was not available.)
Technical evidence
The recommendation above is based on the sources listed here. OEM source means the manufacturer published it; third-party source means a distributor, repair company or reseller states it. Confidence reflects how directly those sources support the recommendation: High — directly supported by manufacturer documentation. Medium — supported by family-level, secondary, or otherwise less-direct evidence. Low — limited or indirect evidence; verify independently before ordering.
OEM / manufacturer sources
Source excerpt“End of Life for remaining PLC-5 processors; migrate to ControlLogix platform”
Source excerpt“the Allen-Bradley PLC-5 control platform ... was discontinued in 2017 ... Migrating PLC-5 controllers to ControlLogix controllers ... Wiring Conversion System hardware (Bulletin 1492) ... candidates for remanufacture and recertification”
Source excerpt“PLC-5/40E (1785-L40E) 48 K ... 2 DH+/Remote I/O ... 1 channel Ethernet only”
Third-party sources
Source excerpt“L40B->L71; L60B->L83E mapping table in reseller migration guide”
Limitation: All lifecycle dates are platform-level; no exact-model page or date is published for the L40B. The reseller L40B-to-1756-L71 memory fork is recorded but not endorsed — size the controller to the application.
Related replacement analyses
- Allen-Bradley / Rockwell 1747-L553 — Related SLC 500 controller.
- Allen-Bradley / Rockwell 1785-L80B — Related PLC-5 controller.
- Allen-Bradley / Rockwell 1771-IBD — Related PLC-5 I/O module.
- Allen-Bradley / Rockwell 1747-L552 — Related SLC 500 controller.
- Allen-Bradley / Rockwell 1785-L60B — Related PLC-5 controller.
- Allen-Bradley / Rockwell 1756-L61 — Migration destination: ControlLogix platform.