Allen-Bradley ControlLogix 1756-L55M12 750KB Memory Controller Module

Overview

The 1756-L55M12 (1756-L55M12) is a high-performance Logix5555 processor designed for the Allen-Bradley ControlLogix platform. This module is engineered to handle complex control engine requirements, providing a multitasking operating environment that supports multiple programming languages including Ladder Logic, Structured Text, and Function Block Diagrams. With 750 Kilobytes of available user memory, it offers a reliable solution for medium-scale industrial applications requiring precise I/O management and fast logic execution.

Technical Specifications and Performance Data

The 1756-L55M12 (1756-L55M12) integrates directly into any slot of a ControlLogix chassis, leveraging the high-speed backplane for data distribution and peer-to-peer communication.

• Memory Configuration: 750 Kilobytes of User RAM (Non-volatile storage available via optional CompactFlash on newer Logix series, but this legacy unit utilizes battery-backed RAM).

• I/O Capacity: Supports a maximum of 128,000 total I/O points.

• Analog Scaling: Capable of managing 4,000 Analog Inputs and 2,000 Analog Outputs.

• Logic Execution Time: Typical program scan time of 0.08 milliseconds (specific to simple logic rungs).

• Current Draw: 1.23 Amps at 5.1V DC; 14 milliamps at 24V DC.

• Thermal Dissipation: Approximately 19.1 BTU per hour.

• Communication Options: Compatible with EtherNet/IP, ControlNet, DeviceNet, and Data Highway Plus through respective communication modules.

• Battery Backup: Compatible with 1756-BA1 or the 1756-BATM externally mounted battery assembly for extended program retention.

Environmental and Physical Standards

The hardware is designed for continuous operation in industrial environments, adhering to strict vibration and temperature tolerances.

• Operational Temperature: 0 to 60 degrees Celsius (32 to 140 degrees Fahrenheit).

• Storage Temperature: -40 to 85 degrees Celsius (-40 to 185 degrees Fahrenheit).

• Humidity: 5% to 95% non-condensing.

• Vibration Resistance: 2.0g @ 10 to 500 Hertz.

• Weight: 0.37 kg (0.81 lbs).

Common Technical Inquiries

How is the user memory partitioned in the 1756-L55M12?The 750KB of memory is shared between data storage and the application code. Unlike legacy PLC-5 systems, the ControlLogix platform allocates memory dynamically based on the tag-based database structure.

Which programming software is required for this module?The 1756-L55M12 (1756-L55M12) is typically programmed using RSLogix 5000 software. The firmware revision of the processor must match the major version of the software project.

What is the purpose of the 1756-BATM?While the 1756-BA1 is a standard internal battery, the 1756-BATM is an optional battery module used for applications where the controller is powered down for long periods, providing significantly higher mAh capacity to preserve memory.