Allen-Bradley 1756 ControlLogix Modules – 1756-TBSH

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 complexes, nuclear power stations, offshore oil & gas platforms, and continuous-process refineries, the 1756 backplane-based system has served as the backbone of safety-critical and high-availability control loops since its commercial introduction in the late 1990s. Its modular chassis architecture — supporting 4, 7, 10, 13, and 17-slot configurations — allows engineers to construct redundant, scalable control nodes without proprietary bus lock-in. The platform's native integration with Rockwell Automation's Studio 5000 Logix Designer environment and its compatibility with EtherNet/IP, ControlNet, DeviceNet, and FOUNDATION Fieldbus makes it the reference standard against which competing DCS and hybrid PLC architectures are measured in process industries.

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform launched commercially circa 1997 as a successor to Rockwell's PLC-5 and SLC 500 families, introducing a producer/consumer network model over ControlNet that eliminated the polling overhead of earlier master/slave topologies. The original 1756-L1 and 1756-L20 processors established the tag-based programming paradigm that persists through current-generation firmware.

The second architectural generation (circa 2003–2008) introduced the 1756-L55 and 1756-L63 controllers with expanded memory and the first native EtherNet/IP bridge modules (1756-ENBT), enabling direct integration with plant-floor Ethernet infrastructure without a dedicated communication coprocessor. This era also saw the introduction of the 1756-CN2 ControlNet bridge and the 1756-DNB DeviceNet scanner, consolidating multi-network topologies onto a single chassis.

The third generation (2010–2018) delivered the L7x controller family (1756-L71 through 1756-L85), featuring non-volatile energy storage (NVS) replacing battery-backed SRAM, dual-port EtherNet/IP on the 1756-EN2T and 1756-EN2TR modules, and the introduction of the 1756-L8xE series with embedded dual-port EtherNet/IP on the CPU itself. Chassis and power supply form factors remained backward-compatible, protecting installed-base investments.

Current-generation hardware (2018–present) centers on the 1756-L8x and forthcoming Logix 5000 v35+ firmware ecosystem. Many L1x through L6x controllers are now in the end-of-life or discontinued phase, creating sustained demand for certified spare and refurbished units to support long-lifecycle plant assets with 20–40 year operational horizons.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Controllers (CPU Modules)

• 1756-L71: 2 MB user memory Logix 5571 controller, standard chassis mount, USB/SD programming port.
• 1756-L72: 4 MB user memory Logix 5572 controller, dual-port EtherNet/IP embedded, SD card slot.
• 1756-L73: 8 MB user memory Logix 5573 controller, high-capacity tag database, SD card slot.
• 1756-L74: 16 MB user memory Logix 5574 controller, large-scale process applications, SD card slot.
• 1756-L75: 32 MB user memory Logix 5575 controller, maximum capacity L7x series, SD card slot.
• 1756-L85E: 40 MB user memory Logix 5585E controller, embedded dual-port EtherNet/IP, current flagship.

Digital Input (DI) Modules

• 1756-IB16: 16-point 24V DC sourcing digital input, 1 ms input filter, group isolated.
• 1756-IB32: 32-point 24V DC sourcing digital input, high-density, 2-slot equivalent footprint.
• 1756-IA16: 16-point 120V AC digital input, individually isolated, 10 ms filter.

Digital Output (DO) Modules

• 1756-OB16E: 16-point 24V DC electronically fused sourcing output, diagnostic feedback per point.
• 1756-OA16: 16-point 120/240V AC triac output, zero-crossing switching, group isolated.

Analog Input/Output (AI/AO) Modules

• 1756-IF16: 16-channel single-ended analog input, ±10V / 0–20 mA, 16-bit resolution.
• 1756-OF8: 8-channel analog output, ±10V / 4–20 mA, 16-bit resolution, individually isolated.

Communication & Network Adapter Modules

• 1756-EN2T: Single-port EtherNet/IP bridge/scanner, 100 Mbps, supports CIP motion and I/O.
• 1756-EN2TR: Dual-port EtherNet/IP bridge with Device Level Ring (DLR) support, 100 Mbps.
• 1756-CN2: ControlNet bridge/scanner module, coax media, redundant media capable.
• 1756-DNB: DeviceNet scanner module, supports up to 64 nodes, explicit and I/O messaging.

Power Supply Modules

• 1756-PA72: 120/240V AC input power supply, 10A @ 1.2V backplane output, standard chassis.
• 1756-PB72: 18–32V DC input power supply, 10A @ 1.2V backplane output, standard chassis.

Wiring & Termination Accessories

• 1756-TBSH: 20-pin spring-clamp terminal block for 1756 I/O modules; tool-free wire termination, accepts 0.2–2.5 mm² conductors, rated 250V / 10A per circuit. Compatible with 1756-IB16, 1756-OB16E, and equivalent 20-pin I/O modules. Eliminates screw-torque variability in high-vibration environments.

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates at 1.2V with a high-speed serial bus that is sensitive to connector oxidation, ESD damage, and firmware version mismatches. DriveKNMS applies the following test protocol to all 1756 modules prior to dispatch:

• Visual inspection: PCB surface, connector pins, and housing for physical damage, corrosion, or counterfeit indicators.
• Backplane communication test: Module seated in a live 1756 chassis; RSLinx Classic used to verify module identity, firmware revision, and fault-free status register.
• I/O functional test: For digital and analog modules, all channels exercised against calibrated signal sources; output modules verified under resistive load.
• Firmware audit: Controller modules verified against Rockwell's published firmware compatibility matrix for the target application revision.
• Terminal block test (1756-TBSH specific): Spring-clamp retention force verified per IEC 60947-7-1; conductor insertion/extraction cycle test performed on all 20 positions.
• Burn-in: Modules operated at rated load for minimum 4 hours at ambient temperature prior to final inspection.