Allen-Bradley 1756 ControlLogix Modules – 1756-IM16I

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform was introduced by Rockwell Automation in 1997 as a successor to the PLC-5 and SLC 500 families, addressing the industry's demand for a scalable, multi-controller chassis architecture. The original 1756 series established the ControlBus backplane standard, enabling up to 17 slots per chassis with peer-to-peer communication between controllers and I/O modules without a dedicated scanner.

The architecture evolved through several distinct generations. Early-generation modules (circa 1997–2004) used Series A hardware with 5V DC backplane logic and supported ControlNet as the primary network backbone. The introduction of EtherNet/IP as a primary I/O network (circa 2003–2007) drove a Series B hardware revision across most catalog numbers, adding diagnostic capabilities and electronic keying enforcement. From 2008 onward, Rockwell introduced the ControlLogix 5570 and later 5580 controllers, which maintained full backward compatibility with existing 1756 I/O modules while adding 64-bit processing, larger memory, and integrated motion over EtherNet/IP (MoE).

Compatibility considerations are critical for maintenance engineers: Series A and Series B modules are physically interchangeable within the same chassis, but firmware-level keying may restrict substitution in systems with strict electronic keying policies. Modules from the original 1756-L1 through 1756-L63 controller era remain operational in 1756 chassis but are no longer manufactured. The 1756-L8x series (ControlLogix 5580) represents the current production standard as of 2026.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Digital Input Modules

• 1756-IM16I: 16-point isolated 120V AC digital input module, channel-to-channel isolation, 10ms input filter
• 1756-IB16: 16-point 10–31.2V DC sourcing digital input, standard density, diagnostic capable
• 1756-IB32: 32-point 10–31.2V DC sourcing digital input, high-density, shared commons
• 1756-IC16: 16-point 48V DC sourcing digital input module, TTL-compatible logic levels
• 1756-IN16: 16-point 10–30V DC sinking digital input, NPN-compatible field devices
• 1756-IA16: 16-point 74–132V AC digital input module, standard industrial AC field wiring
• 1756-IA16I: 16-point isolated 74–132V AC digital input, individual channel isolation

Digital Output Modules

• 1756-OB16E: 16-point electronically fused 10–31.2V DC sourcing digital output, per-point diagnostics
• 1756-OB32: 32-point 10–31.2V DC sourcing digital output, high-density, shared commons
• 1756-OA16: 16-point 74–132V AC digital output, triac-based solid-state switching
• 1756-OA8E: 8-point electronically fused 74–132V AC digital output, diagnostic feedback per point
• 1756-OW16I: 16-point isolated relay output module, Form A contacts, 240V AC / 30V DC rated

Analog I/O Modules

• 1756-IF8: 8-channel analog input, 4–20mA / 0–10V configurable, 16-bit resolution
• 1756-OF8: 8-channel analog output, 4–20mA / 0–10V configurable, 16-bit resolution
• 1756-IF16: 16-channel analog input, high-density process measurement, differential inputs

Controller Modules

• 1756-L71: ControlLogix 5570 controller, 2MB memory, standard processing, EtherNet/IP native
• 1756-L83E: ControlLogix 5580 controller, 40MB memory, dual EtherNet/IP ports, CIP Security capable

Communication & Adapter Modules

• 1756-EN2T: EtherNet/IP communication module, 100Mbps, single port, DLR capable
• 1756-CN2: ControlNet communication module, dual-port coax, redundant media support
• 1756-DNB: DeviceNet scanner module, supports up to 64 nodes per scanner

Power Supply Modules

• 1756-PA72: 120/240V AC input power supply, 10A backplane current, standard chassis
• 1756-PB72: 18–32V DC input power supply, 10A backplane current, DC-powered applications

Sourcing Hard-to-Find & Obsolete 1756 ControlLogix Parts

A significant portion of the 1756 ControlLogix installed base operates on hardware that Rockwell Automation has transitioned to End-of-Life (EOL) or End-of-Support (EOS) status. Modules such as the 1756-L1, 1756-L40, 1756-L60, and early Series A I/O modules are no longer manufactured, yet remain in active service at facilities with 20–30 year operational lifecycles — particularly in nuclear, refining, and municipal water infrastructure where control system replacement projects require multi-year capital planning cycles.

Quality Control for the 1756 ControlLogix Range

The 1756 platform's modular backplane architecture introduces specific failure modes that require targeted test procedures beyond standard power-on verification. DriveKNMS applies the following test protocol to all 1756 series modules prior to shipment:

Backplane Communication Verification: Each module is seated in a live 1756 chassis and interrogated via RSLogix 5000 / Studio 5000 to confirm correct module identity, series, revision, and electronic keying data. Modules that fail to enumerate on the backplane are rejected regardless of visual condition.

I/O Point Functional Test: For digital input modules including the 1756-IM16I, each of the 16 input points is individually stimulated at rated voltage (120V AC for IM16I) and the corresponding status bit is verified in the controller tag database. Channel-to-channel isolation is verified using a 500V DC hipot test between adjacent input commons.

Analog Calibration Check: Analog modules (1756-IF8, 1756-OF8, 1756-IF16) are tested across the full input/output range at 0%, 25%, 50%, 75%, and 100% of span. Linearity error must be within ±0.1% of full scale to pass.