Allen-Bradley 1756-L55 ControlLogix Processor

The Allen‑Bradley 1756‑L55 ControlLogix Processor is the high‑performance CPU in Rockwell Automation’s ControlLogix Series A, designed to reside in a 1756 backplane chassis and execute control logic across I/O, communications, and sequencing modules. This Logix 5555 processor uses memory modules (for example 1756‑L55M22 or 1756‑L55M24) to store control programs and data, with configurations offering up to 750 KB of RAM (L55M22) or up to 3.5 MB (L55M24) with non‑volatile memory options. Typical backplane current is around 1.23 A and the unit dissipates about 5.6 W, roughly 19.1 BTU/hr, reflecting its compact yet capable thermal footprint. The L55 belongs to the ControlLogix family’s Series A lineage and is documented in Rockwell lifecycle notices as discontinued, guiding users to consider newer controllers in the Logic 5555/Logix 555x family for ongoing support. Applications include centralized process and machine control on manufacturing lines, packaging, material handling, and other automation tasks where fast logic execution and integrated I/O coordination are required; it pairs with standard ControlLogix I/O, power supply, and network modules (for example Ethernet/IP or ControlNet via appropriate interface modules) inside a single chassis. For operation, a compatible memory module is required to load and run programs, while the processor communicates with other system components through the 1756 backplane and supported communication modules.