What Is the 1756-L55M12 ControlLogix Processor?
The Allen-Bradley 1756-L55M12 is a ControlLogix 5555 processor module from Rockwell Automation. It provides 750 kilobytes of user memory for data and logic, plus 208 kilobytes of I/O memory. This module manages the control program and communicates with I/O and other controllers across the ControlLogix backplane. Engineers who maintain legacy ControlLogix installations often need this exact catalog number to replace a failed processor or expand an existing chassis. The 1756-L55M12 keeps older machines productive without forcing a full platform migration.
Key Technical Parameters
Memory and I/O Capacity
The 750 kilobytes of RAM supports the application program and tag database. The module handles up to 128,000 maximum I/O points, with analog capacity of 4,000 inputs and 2,000 outputs. This capacity suits medium to large process and discrete control tasks.
Scan Time and Backplane Power
A program scan time of 0.08 milliseconds delivers fast, deterministic execution for time-sensitive logic. The module draws 1.23 Amps at 5 Volts DC and 14 milliamps at 24 Volts DC from the backplane. Confirm your chassis power budget supports these loads before installation.
Physical and Environmental Ratings
The module weighs 0.78 pounds (0.35 kilograms). It operates between 32-140 Fahrenheit (0-60 Celsius) and withstands vibration from 10-500 Hertz. Relative humidity tolerance spans 5-95 percent. These ratings fit standard industrial control cabinets.
Battery Backup
A lithium battery, catalog number 1756-BA1 or 1756-BATM, maintains memory during power loss. Order a replacement only when needed.
Replacement and Upgrade Path
This processor fits organizations running legacy ControlLogix 5555 systems. When a unit fails, downtime costs mount quickly. Sourcing the exact 1756-L55M12 restores operation without rewriting the program or re-engineering the chassis. The module supports ControlNet, EtherNet/IP, DH+, DeviceNet, and universal remote I/O networks, so it integrates with existing communication infrastructure. It also works in redundant controller systems when paired with other 1756-L55 controllers on a ControlNet network. That flexibility protects your prior automation investment.
Where This Processor Fits
Discrete Manufacturing
Assembly lines and packaging equipment rely on fast scan times and high I/O counts. The 0.08 millisecond scan time keeps high-speed logic responsive.
Process Control
Analog I/O capacity of 4,000 inputs and 2,000 outputs supports continuous processes with many measurement points.
Redundant Systems
Paired with other 1756-L55 controllers over ControlNet, this module supports fault-tolerant architectures for critical operations.
Installation and Setup Guidance
Mount the module in a compatible ControlLogix chassis and verify backplane power capacity. Connect programming terminals using 1756-CP3 or 1747-CP3 serial cables. Install a 1756-BA1 or 1756-BATM battery to protect memory. Follow the manufacturer’s installation manual for all wiring and configuration steps.
Maintenance and Reliability
Inspect the module periodically for loose connections and environmental exposure. Replace the lithium battery according to the manufacturer’s schedule. Keep cabinet temperature within the 0-60 Celsius operating range and humidity within 5-95 percent. These practices extend service life and reduce unplanned downtime.
Compatibility and Integration
The 1756-L55M12 communicates over ControlNet, EtherNet/IP, DH+, DeviceNet, and universal remote I/O networks. It works with 1756-CP3 or 1747-CP3 serial cables for programming. For redundant configurations, use ControlNet with other 1756-L55 controllers.
What to Verify Before Buying
Confirm your chassis supports the backplane current draw of 1.23 Amps at 5 Volts DC and 14 milliamps at 24 Volts DC. Check that your application fits within 750 kilobytes of user memory and 128,000 maximum I/O. Verify battery type and communication requirements. SpareTechPLC supplies industrial automation parts and can help confirm availability. Please verify current lifecycle status and availability with SpareTechPLC before ordering.
Frequently Asked Questions
What memory does the 1756-L55M12 provide?
It offers 750 kilobytes of user memory for data and logic, plus 208 kilobytes of I/O memory.
Which battery does this processor use?
Use a 1756-BA1 or 1756-BATM lithium battery.
What communication networks does it support?
It supports ControlNet, EtherNet/IP, DH+, DeviceNet, and universal remote I/O networks.
Can it run in a redundant system?
Yes, when paired with other 1756-L55 controllers on a ControlNet network.
What is the program scan time?
The program scan time is 0.08 milliseconds.
