Allen-Bradley 1756 ControlLogix Modules

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series: Comprehensive Module Range and Technical Overview

The Allen-Bradley 1756 ControlLogix platform, developed by Rockwell Automation, is one of the most widely deployed programmable automation controller (PAC) architectures in global heavy industry. Installed across petrochemical complexes, nuclear power stations, offshore oil platforms, pulp and paper mills, and continuous-process refineries, the 1756 chassis-based system provides deterministic control, high-availability redundancy, and a modular I/O architecture that has made it the reference standard for safety-critical and process-critical applications since its commercial introduction in 1997.

The platform's installed base spans hundreds of thousands of chassis worldwide. Its longevity in service — with many installations exceeding 20 years of continuous operation — creates sustained demand for spare modules, replacement CPUs, and lifecycle extension support. DriveKNMS maintains a dedicated inventory of both current-production and discontinued 1756 modules to support this installed base.

The Evolution of 1756 ControlLogix Architecture

The 1756 platform has undergone four distinct architectural generations since 1997, each maintaining backward chassis compatibility while expanding processing capacity, network capability, and safety certification scope.

Generation 1 (1997–2003): The original 1756-L1 and 1756-L20 processors established the chassis-and-backplane model. Communication was primarily via 1756-DHRIO (Data Highway Plus / Remote I/O) and 1756-CNB (ControlNet Bridge) modules. I/O density was limited to 16-point discrete modules.

Generation 2 (2003–2010): Introduction of the Logix5563 and Logix5573 processors (1756-L63, 1756-L73) with expanded memory and EtherNet/IP as a primary network. The 1756-ENBT and 1756-EN2T modules became the standard Ethernet bridge. High-density 32-point I/O modules were introduced.

Generation 3 (2010–2018): The L7x processor family (1756-L71 through 1756-L85E) introduced integrated EtherNet/IP ports, eliminating the need for a separate Ethernet bridge in many topologies. The 1756-EN2TR added Device Level Ring (DLR) support for fault-tolerant ring networks. SIL 2 safety certification via GuardLogix (1756-L71S, 1756-L73S) became standard.

Generation 4 / Current (2018–present): The V32 and V33 firmware controllers (1756-L81E through 1756-L85E) support Logix Designer Application v32+, Ethernet-based redundancy without a dedicated 1756-SYNCH module, and CIP Security for encrypted controller communications. Legacy modules from Generations 1 and 2 are now classified as End of Life (EOL) or End of Sale (EOS) by Rockwell Automation, creating critical demand for aftermarket sourcing.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Controllers (CPU Modules)

• 1756-L71: Logix5571 controller, 2MB memory, single Ethernet port, standard ControlLogix.
• 1756-L73: Logix5573 controller, 8MB memory, dual Ethernet ports, high-capacity applications.
• 1756-L75: Logix5575 controller, 32MB memory, large-scale process control applications.
• 1756-L81E: Logix5581 controller, 3MB memory, integrated dual-port EtherNet/IP, Gen 4.
• 1756-L85E: Logix5585 controller, 40MB memory, maximum capacity Gen 4 CPU.
• 1756-L71S: GuardLogix 5571S safety controller, SIL 2 / PLe certified, 2MB standard + 1MB safety.
• 1756-L73S: GuardLogix 5573S safety controller, 8MB standard + 4MB safety memory.

Communication & Adapter Modules

• 1756-EN2T: EtherNet/IP bridge module, single copper port, 100 Mbps, standard rack communication.
• 1756-EN2TR: EtherNet/IP bridge, dual copper ports, Device Level Ring (DLR) topology support.
• 1756-EN3TR: EtherNet/IP bridge, dual copper ports, CIP Sync time synchronization support.
• 1756-CNB: ControlNet bridge module, coax media, legacy process network integration.
• 1756-DHRIO: Data Highway Plus / Remote I/O bridge, legacy DH+ network connectivity.
• 1756-PSCA2: Power supply chassis adapter, connects remote chassis to local chassis backplane via fiber.
• 1756-RIO: Remote I/O scanner module, legacy RIO network master for distributed I/O racks.

Discrete I/O Modules

• 1756-IB16: 16-point 24VDC digital input module, sink type, standard discrete sensing.
• 1756-OB16E: 16-point 24VDC digital output module, electronically fused, source type.
• 1756-IA16: 16-point 120VAC digital input module, isolated, AC field device interface.
• 1756-OA16: 16-point 120/240VAC digital output module, triac output, AC load switching.

Analog I/O Modules

• 1756-IF16: 16-channel analog input module, 4–20mA / 0–10V, high-density process measurement.
• 1756-OF8: 8-channel analog output module, 4–20mA / 0–10V, process control valve interface.
• 1756-IR6I: 6-channel RTD/resistance input module, isolated, temperature measurement.
• 1756-IT6I: 6-channel thermocouple input module, isolated, J/K/T/E/R/S/B type support.

Power Supply Modules

• 1756-PA72: 120/240VAC power supply, 13A @ 5VDC backplane output, standard chassis power.
• 1756-PB72: 18–32VDC power supply, 13A @ 5VDC, DC-powered installation environments.
• 1756-PA75R: Redundant-rated 120/240VAC power supply, used in 1756-SB redundancy chassis.

Sourcing Hard-to-Find & Obsolete 1756 ControlLogix Parts

Rockwell Automation has issued End of Sale (EOS) notices for a significant portion of the Generation 1 and Generation 2 1756 module catalog, including the 1756-L60M03SE, 1756-L63, 1756-ENBT, 1756-CNB/E, and 1756-DHRIO. For facilities operating these legacy systems — particularly those under long-term maintenance contracts or operating in jurisdictions where control system replacement requires regulatory re-approval — sourcing replacement modules from the aftermarket is the only viable path to continued operation.

DriveKNMS maintains a dedicated inventory of discontinued 1756 modules sourced from decommissioned plant equipment, authorized surplus channels, and factory-sealed legacy stock. All modules are verified against Rockwell Automation firmware compatibility matrices prior to dispatch. We provide documentation packages including firmware version records, test reports, and traceability certificates on request.

For facilities requiring long-term lifecycle support agreements covering the 1756 platform, DriveKNMS offers scheduled inventory reservation, priority dispatch SLAs, and technical consultation on migration pathways to current-generation Logix controllers.

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates at 5VDC with a proprietary high-speed serial bus. Modules with degraded backplane connectors, corrupted firmware, or failed ASIC components will not enumerate correctly on the chassis and may cause rack-wide faults. DriveKNMS applies a structured test protocol to all 1756 modules prior to shipment:

• Backplane connector inspection: Pin alignment, contact plating integrity, and insertion force measurement against Rockwell Automation mechanical tolerances.
• Power rail verification: 5VDC and 24VDC rail loading tests under simulated backplane current draw.
• Firmware enumeration test: Each module is installed in a live 1756 chassis running current Logix Designer firmware. Successful enumeration, correct module identity string, and absence of fault codes are required for pass status.
• I/O channel functional test: For analog modules, all channels are tested at 0%, 50%, and 100% of rated input/output range. For discrete modules, all points are exercised through a full on/off cycle.
• Communication module loopback test: EtherNet/IP, ControlNet, and DH+ modules are tested for packet transmission integrity and correct CIP object response.
• Thermal cycling: Modules flagged as previously installed in high-ambient environments undergo 4-hour thermal cycling between 0°C and 60°C prior to final test.