Allen-Bradley 1756-L1 Logix 5550 Processor Unit

The Allen-Bradley 1756-L1 Logix 5550 Processor Unit is the original ControlLogix 5550 CPU in Rockwell Automation’s Logix 5500 family, engineered for scalable, modular automation with the 1756 I/O backplane. It ships with 160 KB of user memory and supports memory expansion through the 1756‑M1, M2, or M3 modules; installing the 1756‑M2 adds 1 MB of user memory, enabling larger programs and data tables within a single chassis. In operation, the base L1 consumes backplane current of about 0.65 A at 5 VDC and 0.02 A at 24 VDC, while the L1M2 expansion increases backplane draw to roughly 1.05 A at 5 VDC (0.02 A at 24 VDC). The 1756‑L1 family supports ControlNet I/O and Universal Remote I/O configurations, reflecting its role in mid‑to‑large ControlLogix deployments. The system can accommodate up to 128,000 total I/O points across the chassis, providing substantial capacity for mixed discrete and analog I/O in manufacturing and process environments. Paired with the 1756‑M2 and compatible I/O modules, it enables scalable architectures for automation projects that require a robust, field‑proven PLC platform with ample memory and flexible I/O topology.