Description

The Allen-Bradley 1756-L73 is a high-performance programmable automation controller (PAC) from the ControlLogix 5570 family, manufactured by Rockwell Automation. Engineered for demanding industrial automation applications, it provides a scalable, multi-discipline control architecture capable of managing discrete, motion, process, and safety operations. The 1756-L73 utilizes a high-speed backplane and internal processing core to deliver deterministic loop execution and high-capacity data handling.

Commercial Availability & Procurement

Technical Specifications

Core Hardware Features & Energy Management

The 1756-L73 represents a major architectural shift over legacy ControlLogix 5560 (L6x) controllers by eliminating the reliance on lithium batteries for volatile memory retention.

Energy Storage Module (ESM) Tech

The front face of the controller houses a removable, capacitor-based Energy Storage Module (typically the 1756-ESMCAP).

 [ System Power Loss ] ──► [ ESM Supercapacitors Disengage ] ──► [ RAM Data Flashed to Onboard NAND ]
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                                                                  [ 100% Battery-Less Retention ]

When a sudden power blackout occurs, the ESM immediately delivers a burst of localized power to the CPU. This allows the controller to write the entire contents of its volatile project RAM into internal non-volatile NAND flash memory before completely shutting down.

Critical Field Note: Because the module uses supercapacitors rather than a chemical cell, it does not degrade over time or require routine preventative maintenance replacements. However, if the ESM is removed or reaches its end-of-life cycle, the controller will flag a minor fault on the front scrolling display (“ESM Charging” or “ESM Error”). The logic will still execute, but the program will not survive a hard power cycle if the module is completely dead.

Front Panel Scrolling Display

The integrated 4-character alphanumeric display provides real-time status and error codes, bypassing the need to connect a laptop for baseline troubleshooting. It cycles through standard system information (such as the controller name, active IP address of bridged modules, and current firmware revision) or displays hard fault codes (e.g., “OK,” “TEST,” or specific “MNR” fault strings).

Field Integration & Firmware Guardrails

When upgrading, commissioning, or hot-swapping a 1756-L73 controller inside a ControlLogix chassis, observe the following field protocols:

Firmware Major Revision Matching

The 1756-L73 is shipped from the factory with a baseline “boot firmware” (typically revision 1.xx). Before it can accept a user application, you must use Rockwell’s ControlFlash utility to flash a specific major and minor firmware revision that matches the version of your programming software.

• The 1756-L73 supports firmware environments from Revision 20 up to Revision 34 and beyond within Studio 5000 Logix Designer / RSLogix 5000.

• Ensure that the major firmware version chosen aligns with all networked communication bridges (e.g., 1756-EN2TR) and remote I/O chassis adapters across the factory automation architecture to avoid communication connection drops.

USB Programming Constraints

The front-mounted USB 2.0 port is designed exclusively for temporary engineering activities such as local programming modifications, firmware flashing, and online diagnostics. It is configuration-free and acts as a standard virtual serial connection. Note: The USB port is not intended for permanent connection to HMIs, SCADA networks, or plant-wide data loggers; all permanent industrial communications must route through separate, dedicated slot-mounted network modules like the 1756-EN2T or 1756-CN2.

Frequently Asked Questions

Q: Can a 1756-L73 be installed in a standard legacy ControlLogix chassis alongside L6x processors?

Yes. The 1756-L73 is fully compatible with standard ControlLogix Series A and Series B backplanes (such as the 1756-A4, 1756-A7, 1756-A10, and 1756-A17 racks) and standard 1756 power supplies. It can reside in the same physical chassis as older processors, provided that they do not attempt to control the exact same physical I/O slots simultaneously without proper producer/consumer synchronization configuration.

Q: What is the mechanical procedure for performing a firmware flash lock?

The front face plate contains a three-position key switch: RUN, REM (Remote), and PROG (Program). To prevent unauthorized personnel or automated network utilities from modifying or flashing the controller’s internal firmware while online, switch the mechanical key to the RUN position. In this state, all software configuration downloads, firmware rewrites, and runtime logic edits are strictly blocked.

Q: Why does the controller fail to boot and display a “NAND Flash Error” after an unscheduled power outage?

This indicates that the project preservation cycle failed during the power down. This symptom typically occurs if the power supply was cycled on and off rapidly (“chattering”), preventing the ESM capacitors from fully recharging between cycles. It can also point to a physically unseated or corrupted Secure Digital (SD) card inside the front compartment slot. Reseat the SD card, check the ESM charging state, and redownload the project file via the Studio 5000 environment.