Allen-Bradley 1756 ControlLogix Modules – 1756-RMC1

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

The Allen-Bradley 1756 ControlLogix platform is one of the most widely deployed programmable automation controller (PAC) architectures in global heavy industry. Installed across petrochemical refineries, nuclear power generation facilities, offshore oil & gas platforms, pulp and paper mills, and large-scale water treatment infrastructure, the 1756 chassis-based system has served as the backbone of process and discrete control since its commercial introduction in the late 1990s. Its modular backplane architecture, deterministic communication via ControlNet and EtherNet/IP, and redundancy-capable CPU design have made it the reference standard for safety-critical and high-availability applications. The 1756 series supports chassis sizes from 4-slot to 17-slot configurations, accommodating mixed I/O, motion, communication, and controller modules within a single rack. Its producer/consumer network model enables efficient data exchange across distributed control nodes without polling overhead.

The Evolution of 1756 ControlLogix Architecture

The 1756 ControlLogix platform was introduced by Rockwell Automation in 1997 as a successor to the PLC-5 and SLC 500 families. The initial release established the chassis-and-module paradigm with the 1756-L1 processor, operating on a proprietary backplane at 200 Mbps. The architecture underwent its first major revision with the introduction of the Logix5550 and Logix5555 processors, which expanded memory capacity and added ControlNet scheduling capabilities.

The second architectural generation arrived with the L6x processor family (Logix5561, Logix5562, Logix5563), introducing expanded I/O tree capacity, enhanced motion coordination, and support for Integrated Motion on EtherNet/IP. The L7x generation (Logix5570, Logix5571, Logix5572, Logix5573, Logix5574, Logix5575) represented a significant leap: 64-bit processing, up to 40 MB user memory, embedded EtherNet/IP ports, and support for CIP Safety and CIP Motion simultaneously. The current L8x generation (Logix5580 series) introduced a multi-core architecture, Studio 5000 Logix Designer integration, and Nano Edge computing capabilities.

Compatibility across generations is a persistent engineering concern. Older 1756-A4, 1756-A7, and 1756-A10 chassis remain electrically compatible with modern modules, but firmware dependencies, EDS file versions, and RSLogix 5000 project compatibility must be validated before cross-generation substitution. Modules from the L1/L2 era are now fully discontinued and require lifecycle extension sourcing.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Controllers

• 1756-L71: Logix5571 controller, 2 MB memory, single Ethernet port, L7x generation standard CPU.
• 1756-L72: Logix5572 controller, 4 MB memory, dual Ethernet ports, supports CIP Motion.
• 1756-L73: Logix5573 controller, 8 MB memory, dual Ethernet, high-axis-count motion.
• 1756-L74: Logix5574 controller, 16 MB memory, dual Ethernet, large-scale process applications.
• 1756-L75: Logix5575 controller, 32 MB memory, maximum L7x capacity, refinery-grade deployments.
• 1756-L85E: Logix5585E controller, L8x generation, 40 MB memory, multi-core, embedded dual Ethernet.

Digital I/O Modules

• 1756-IB16: 16-point 24VDC digital input module, sink type, standard discrete input.
• 1756-IB32: 32-point 24VDC digital input module, high-density discrete input for space-constrained racks.
• 1756-OB16E: 16-point 24VDC digital output module, electronically fused, diagnostics-capable.
• 1756-OB32: 32-point 24VDC digital output module, high-density discrete output.
• 1756-IA16: 16-point 120VAC digital input module, standard AC discrete input.
• 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, 4–20 mA / 0–10V, 16-bit resolution, process instrumentation.
• 1756-OF8: 8-channel analog output module, 4–20 mA / 0–10V, 16-bit, valve and actuator control.
• 1756-IR6I: 6-channel RTD/resistance input module, isolated, temperature measurement.
• 1756-IT6I: 6-channel thermocouple input module, isolated, multi-type TC support.

Communication & Network Adapter Modules

• 1756-EN2T: EtherNet/IP communication module, single copper port, 100 Mbps, standard network bridge.
• 1756-EN2TR: EtherNet/IP module with dual copper ports, Device Level Ring (DLR) support, fault-tolerant topology.
• 1756-CN2: ControlNet communication module, dual coax ports, scheduled and unscheduled messaging.
• 1756-DNB: DeviceNet scanner module, master node for DeviceNet field device networks.
• 1756-RMC1: Fiber optic cable assembly for ControlLogix redundancy chassis interconnect, single-mode, 1-meter length. Used to link primary and secondary chassis in 1756 redundancy configurations.

Power Supply Modules

• 1756-PA72: 120/240VAC input power supply, 13A backplane output, standard chassis power.
• 1756-PB72: 18–32VDC input power supply, 13A backplane output, DC-powered installations.
• 1756-PSCA2: Power supply chassis adapter for extended chassis configurations.

Redundancy Modules

• 1756-RM2: Redundancy module, second generation, manages primary/secondary chassis synchronization.
• 1756-SYNCH: Synchronization cable for 1756-RM redundancy module pairs.

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates at 200 Mbps with a proprietary protocol governing slot addressing, module keying, and real-time data exchange. Quality verification for 1756 modules requires test equipment and procedures specific to this architecture. Generic PLC testers are insufficient for validating backplane communication integrity or I/O channel accuracy.

DriveKNMS applies the following verification procedures to all 1756 series units:

• Backplane communication test: Each module is seated in a live 1756 chassis and verified for correct slot recognition, module identity response, and error-free communication over a minimum 30-minute burn-in cycle.
• I/O channel calibration: Analog modules (IF, OF, IR, IT series) undergo per-channel signal injection and measurement against factory tolerance specifications using calibrated reference instruments.
• Firmware version audit: Controller and communication modules are checked for firmware revision and compatibility with current Studio 5000 / RSLogix 5000 project requirements.
• Redundancy module synchronization test: 1756-RM2 and associated fiber cable assemblies including 1756-RMC1 are tested in a paired chassis configuration to verify switchover timing and link integrity.
• Visual and mechanical inspection: Connector pins, locking tabs, module labels, and PCB condition are inspected under magnification. Units with evidence of field repair, re-marking, or counterfeit indicators are rejected.