Introduction to the Allen-Bradley 1756-L55M12
Is your ControlLogix system down because a legacy processor failed? The Allen-Bradley 1756-L55M12 processor module keeps your line running. This Logix5555 controller carries 750 kilobytes of user memory for data and logic. It also provides 208 kilobytes of I/O memory. As a result, it handles demanding control tasks in older installations. This module belongs to the trusted ControlLogix series from Rockwell Automation. It fits directly into your existing chassis. Therefore, you avoid a full system overhaul. SpareTechPLC supplies this processor to plants that need a reliable drop-in replacement.
Key Technical Specifications
The 1756-L55M12 delivers solid performance for mid-range control applications. Its 750 KB RAM manages complex logic and data handling. The processor supports up to 128,000 maximum I/O points. For analog signals, it handles 4,000 inputs and 2,000 outputs. The program scan time is 0.08 milliseconds, which ensures fast execution of control routines. Backplane current draw is 1.23 Amps at 5 Volts DC and 14 milliamps at 24 Volts DC. The module weighs just 0.78 pounds (0.35 kilograms). It operates in temperatures from 32 to 140 degrees Fahrenheit (0 to 60 degrees Celsius). Relative humidity tolerance ranges from 5 to 95 percent. The unit withstands vibration from 10 to 500 Hertz. A lithium battery (1756-BA1 or 1756-BATM) protects memory during power loss.
Comparison with Similar ControlLogix Processors
| Feature | 1756-L55M12 | Typical 1756-L55 Series |
|---|---|---|
| User Memory | 750 KB | Varies by model |
| Max I/O | 128,000 | Varies by model |
| Analog I/O | 4,000 In / 2,000 Out | Varies by model |
| Backplane Current (5V DC) | 1.23 A | Varies by model |
| Battery | 1756-BA1 or 1756-BATM | Same battery family |
This comparison helps you confirm the 1756-L55M12 meets your memory and I/O needs before ordering.
Replacement and Upgrade Guide
Many plants still run ControlLogix systems with Logix5555 processors. When a processor fails, downtime costs escalate quickly. The 1756-L55M12 serves as a direct replacement for existing 1756-L55 installations. You do not need to rewrite your program or rewire the chassis. Simply match the catalog number and verify your memory requirements. This module supports communication through ControlNet, EtherNet/IP, DH+, DeviceNet, and universal remote I/O networks. It also works in redundant controller systems when paired with other 1756-L55 controllers on a ControlNet network. Before ordering, confirm your current processor model and memory usage. SpareTechPLC offers this module for buyers who need a fast, reliable replacement.
Installation and Setup Guidance
Installing the 1756-L55M12 follows standard ControlLogix procedures. First, verify that your chassis has an open slot and adequate power. Check the backplane current requirements: 1.23 Amps at 5 Volts DC and 14 milliamps at 24 Volts DC. Next, insert the module firmly into the slot. Connect your communication cables using the 1756-CP3 or 1747-CP3 serial cables. For redundant systems, ensure all controllers reside on a ControlNet network. After installation, download your program and verify scan time performance. The 0.08 millisecond scan time supports responsive control. Always follow Rockwell Automation’s installation manual for detailed procedures.
Maintenance and Reliability
The 1756-L55M12 uses a lithium battery (1756-BA1 or 1756-BATM) to maintain memory during power outages. Replace the battery only when needed. Inspect the module periodically for signs of overheating or loose connections. Operating temperature must stay between 0 and 60 degrees Celsius. Keep relative humidity between 5 and 95 percent (noncondensing). The module tolerates vibration from 10 to 500 Hertz. For maximum reliability, follow your plant’s preventive maintenance schedule. Regular inspection helps prevent unexpected downtime and extends module life.
Compatibility and Integration
The 1756-L55M12 integrates with multiple communication networks. It supports ControlNet, EtherNet/IP, DH+, DeviceNet, and universal remote I/O. This flexibility allows you to connect to existing plant networks without major changes. The module also works with other 1756-L55 controllers in redundant configurations. Use the 1756-CP3 or 1747-CP3 serial cables for programming and communication. The processor has a wiring category of 2 on its communication ports. It also provides 30 Volts of continuous isolation. These features ensure safe, reliable integration with your control system.
Frequently Asked Questions
What is the memory capacity of the 1756-L55M12?
The 1756-L55M12 provides 750 kilobytes of user memory for data and logic. It also includes 208 kilobytes of I/O memory.
Which battery does the 1756-L55M12 use?
This processor uses a lithium battery with catalog number 1756-BA1 or 1756-BATM. Replace it only when needed.
Can I use the 1756-L55M12 in a redundant system?
Yes, you can use this controller with other 1756-L55 controllers in a redundant system. All controllers must be on a ControlNet network.
What communication protocols does the 1756-L55M12 support?
The module supports ControlNet, EtherNet/IP, DH+, DeviceNet, and universal remote I/O networks.
What is the operating temperature range for the 1756-L55M12?
The operating temperature range is 0 to 60 degrees Celsius (32 to 140 degrees Fahrenheit).
