- 1756-l55m12_a_logix5555_processor_750kb_memory
Technical Specifications
| Parameter Name | Parameter Value |
|---|---|
| Product Model | 1756-L55M12 |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Product Type | ControlLogix Logix5555 Processor Module |
| Series | ControlLogix 1756 |
| User Memory (RAM) | 750 KB |
| I/O Memory | 208 KB |
| Maximum Discrete I/O | 128,000 points |
| Maximum Analog I/O | 4,000 inputs / 2,000 outputs |
| Program Scan Time | 0.08 ms |
| Backplane Current (5V DC) | 1.23 A |
| Backplane Current (24V DC) | 14 mA |
| Power Dissipation | 5.6 W |
| Isolation Voltage | 30V continuous (basic insulation) |
| Operating Temperature | 0°C to 60°C |
| Battery | 1756-BA1 or 1756-BATM |
| Memory Board Required | 1756-M12 (no non-volatile) or 1756-M22 (with non-volatile) |
| Lifecycle Status | Discontinued |
Main Features and Advantages
The 1756-L55M12 delivers a balanced combination of processing capability and memory capacity that suited it well to mid-complexity control tasks during its active production life. The 0.08-millisecond program scan time provides deterministic execution for ladder logic, function block, and structured text programs, ensuring responsive control of fast-changing processes . The 750 KB user memory accommodates substantial tag databases and program routines, while the separate 208 KB I/O memory prevents tag and logic storage from competing with I/O data for the same memory pool—a design choice that contributes to predictable controller performance under varying I/O loads.
The 1756-L55M12 supports redundant controller configurations when paired with a second 1756-L55 controller over a ControlNet network, providing bumpless switchover for critical processes where controller failure cannot be tolerated . The controller also includes a built-in RS-232 serial port for DF1 protocol communication, enabling direct connection to programming terminals, SCADA systems, and DF1-compatible devices without requiring an additional communication module . For network integration, the backplane supports a wide range of 1756 communication modules, allowing the 1756-L55M12 to participate in ControlNet, EtherNet/IP, DeviceNet, and DH+ architectures as plant infrastructure evolved.
The memory board architecture of the 1756-L55M12 introduces a maintenance consideration that also serves as a practical advantage in some scenarios. Because the 1756-M12 memory board is a separate component, replacing a failed controller does not necessarily require reprogramming from scratch—the existing memory board can be transferred to the replacement 1756-L55M12, preserving the user program and configuration . However, firmware revision compatibility between the controller and memory board must be verified before transfer, as the requires firmware revision 10.28 or later to accept certain memory board types .
