Allen-Bradley 1756-L55 ControlLogix Processor Module

The Allen-Bradley 1756-L55, also cataloged as the 1756-L55 Processor Module, operates as a dedicated hardware component for central logic processing within ControlLogix chassis platforms. The base unit features no integrated user memory onboard, requiring the installation of an optional 1756-Mxx series nonvolatile memory board to store application routines and system tag databases. The processor executes multi-tasking control routines, managing real-time cyclic I/O polling and deterministic data transfer across the chassis backplane without relying on external coprocessor assemblies.

Suffix Breakdown & Model Matrix

Hardware Specifications

ControlLogix Deterministic Networks & Firmware Synchronization

The module communicates over the local ControlLogix backplane using EtherNet/IP deterministic networks and CIP interface logic. Backplane bus communication velocity guarantees deterministic, high-speed data exchanges between the CPU card and local or remote I/O chassis. Firmware flash compatibility via RSLogix 5000 / Studio 5000 enables non-destructive system updates, ensuring firmware synchronization across chassis expansion slots without physical alterations to module memory boards.

Frequently Asked Questions

Q: Can the 1756-L55 base processor execute application programs without a 1756-Mxx memory expansion board?

A: No, the 1756-L55 base unit contains no onboard user memory. It requires a compatible 1756-Mxx expansion card (such as 1756-M12, 1756-M13, 1756-M14, or 1756-M24) to store program logic and system tag configurations.

Q: Does the 1756-L55 processor support Removal and Insertion Under Power (RIUP)?

A: Yes, the 1756-L55 supports Removal and Insertion Under Power (RIUP) within a powered ControlLogix rack. However, removing an active processor immediately stops controller task execution and transitions connected field output modules into their configured fault states.

Field Installation Guidelines

• Ensure backplane chassis grounding strictly complies with IEEE 1100 standards by establishing a direct low-impedance connection between the rack ground lug and enclosure star ground point.
• Ensure any 1756-Mxx memory expansion board is fully seated and mechanically locked onto the 1756-L55 main board prior to inserting the processor into the chassis slot.
• Align the circuit board edges with top and bottom chassis guides, sliding the controller unit firmly into the chassis slot until both upper and lower latches click into place.
• Maintain a minimum vertical clearance distance of 50 mm (2 inches) above and below the ControlLogix chassis frame to facilitate thermal convection across module cooling vents.