Allen-Bradley ControlLogix 1756-L1M2 1MB Logix5550 Controller Processor Module

Module Overview

The 1756-L1M2 is a foundational processor module within the Allen-Bradley ControlLogix 5550 series. Engineered for high-speed discrete and process control, this module features 1MB of expandable non-volatile memory, allowing for robust program storage and complex data handling. As a member of the 1756 chassis-based system, the 1756-L1M2 leverages a producer-consumer communication model, which optimizes network bandwidth by allowing multiple nodes to consume the same data simultaneously. This processor is an ideal choice for legacy system maintenance and specialized industrial applications requiring a reliable, modular control engine.

Detailed Engineering Specifications

The 1756-L1M2 draws minimal power from the backplane, ensuring thermal efficiency even in high-density chassis configurations.

• Processor Type: Logix5550 Modular Controller

• User Memory: 1 Megabyte (Expandable)

• Backplane Current (5.1V DC): 120 milliamps

• Backplane Current (24V DC): 2 milliamps

• Power Dissipation: 4.1 Watts maximum (@ 60°C)

• Isolation Voltage: 30V Continuous (Basic Insulation Type)

• Operating Current (Min): 2 milliamps @ 10V DC

• Operating Current (Max): 3.5 milliamps @ 30V DC

• Off-State Input Current (Max): 1.5 milliamps

• Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Storage Temperature: -40°C to 85°C (-40°F to 185°F)

• Vibration Resistance: 2G @ 10 to 500 Hz

• Physical Weight: 0.81 lbs (0.37 kg)

• Slot Width: Single-slot occupancy

Memory Management and Expansion

A key feature of the 1756-L1M2 is its modular memory architecture. The 1MB of onboard memory can be supplemented with 1756-M1, -M2, or -M3 expansion memory modules to accommodate larger rungs of ladder logic or extensive tag databases. To ensure data integrity during power cycles, the processor utilizes a lithium battery (typically the 1756-BA1) to maintain the volatile RAM. For permanent backup, the user program can be saved to non-volatile storage, protecting the system against long-term power loss in remote environments.

System Compatibility

The 1756-L1M2 is compatible with all standard 1756 ControlLogix chassis (e.g., 1756-A4, -A7, -A10) and can be placed in any available slot. It integrates seamlessly with a wide range of communication modules, including EtherNet/IP (1756-ENBT), ControlNet (1756-CNB), and DeviceNet (1756-DNB). Programming and configuration are handled through RSLogix 5000 software, supporting Ladder Diagram (LD), Structured Text (ST), and Function Block Diagram (FBD) languages.

Technical FAQ

Can the 1756-L1M2 be used in a redundant controller setup?

The 5550 series processors like the 1756-L1M2 generally do not support the high-speed redundancy sync required for modern bumpless transfer. For redundancy applications, the 1756-L6x or L7x series is recommended.

What happens if the battery fails on this module?

If the battery (1756-BA1) is depleted and the chassis loses power, the volatile user program and tag data will be lost. It is critical to monitor the "BATT" LED on the front of the processor and replace the battery while the rack is powered to preserve memory.

Is this processor compatible with Studio 5000?

The 1756-L1M2 is a legacy controller primarily supported by RSLogix 5000 (Versions 10 through 13). Newer versions of Studio 5000 generally target the L7 and L8 hardware generations.