Allen-Bradley ControlNet Modules – 1786-TPS

Technical Dossier

Product Details And Specifications

Allen-Bradley ControlNet Series Technical Notes

The Allen-Bradley ControlNet platform is a deterministic, repeatable industrial network protocol developed by Rockwell Automation. It operates at 5 Mbps over RG-6 coaxial cable and supports both time-critical I/O data and non-time-critical messaging on a single physical medium. ControlNet is deployed across the most demanding continuous-process environments globally — including petrochemical refineries, nuclear power generation facilities, offshore oil platforms, and large-scale chemical manufacturing plants. Its scheduled and unscheduled communication model makes it the preferred backbone for safety-critical and high-availability automation architectures where determinism is non-negotiable. The 1786-TPS, a 1-meter coaxial straight T-tap, is a fundamental physical-layer component in every ControlNet segment installation.

The Evolution of ControlNet Architecture

ControlNet was introduced by Allen-Bradley in the mid-1990s as a successor to the proprietary Data Highway Plus (DH+) network, designed to address the growing need for deterministic, high-speed communication between PLCs, I/O chassis, and HMI systems. The original ControlNet 1.0 specification established the core CTDMA (Concurrent Time Domain Multiple Access) media access method, which remains the protocol's defining characteristic.

Early deployments used the 1786-series physical media components — taps, cables, and terminators — to build trunk-and-drop topologies. The architecture evolved through several generations of scanner and adapter modules, from the original 1771-series PLC-5 ControlNet scanners to the 1756-CNB and 1756-CNBR bridge modules for the ControlLogix platform. Redundant media (Channel A and Channel B) support was introduced to meet the uptime requirements of continuous-process industries, with the 1756-CNBR providing dual-channel redundancy.

As EtherNet/IP matured through the 2010s, Rockwell Automation positioned it as the strategic successor to ControlNet for new installations. However, the installed base of ControlNet systems in heavy industry remains substantial. Many facilities operate on 20–30 year asset lifecycles, making long-term spare parts availability for the 1786-series physical media components and 1756-CNB scanner modules a critical operational requirement. ControlNet is now in a mature/end-of-life phase for new design, but active lifecycle support for existing installations remains commercially significant.

ControlNet Full Catalog & Functionalities (SKU List)

Physical Media — T-Taps & Coaxial Connectors

• 1786-TPS: 1 m coaxial straight T-tap for ControlNet trunk segment connection.
• 1786-TPYR: Right-angle T-tap, 1 m, for space-constrained panel installations.
• 1786-TPR: Right-angle T-tap without cable, field-wireable configuration.
• 1786-TP: Standard straight T-tap without pre-attached cable drop.
• 1786-BNC: BNC terminator plug for ControlNet coaxial trunk termination.
• 1786-BNCP: BNC terminator plug with protective cap for unused ports.

Cables & Trunk Media

• 1786-RG6: Bulk RG-6 coaxial cable, sold per meter, for ControlNet trunk construction.
• 1786-CP: Pre-assembled coaxial cable assembly for drop connections.
• 1786-CPNM: 1 m coaxial cable, N-type male connectors, for repeater connections.

Repeaters & Media Extenders

• 1786-RPT: ControlNet coaxial repeater module, extends segment length up to 1000 m.
• 1786-RPCD: ControlNet fiber optic repeater, single-mode, for long-distance or electrically noisy environments.

ControlNet Scanner / Bridge Modules — ControlLogix Platform

• 1756-CNB: ControlNet bridge module for 1756 ControlLogix chassis, single channel.
• 1756-CNBR: ControlNet bridge module, dual-channel redundant media, for high-availability applications.
• 1756-CN2: ControlNet bridge module, Series B, enhanced diagnostics and network update time performance.
• 1756-CN2R: ControlNet bridge module, Series B, dual-channel redundant media.

ControlNet Scanner Modules — CompactLogix / SoftLogix

• 1769-SDN: DeviceNet scanner for CompactLogix (note: ControlNet bridging via 1756-CNB in linked chassis).
• 1784-PCICS: PCI-bus ControlNet interface card for SoftLogix and PC-based control applications.
• 1784-U2CN: USB-to-ControlNet interface for programming, diagnostics, and network configuration.

ControlNet Adapter Modules — Remote I/O

• 1794-ACN15: FLEX I/O ControlNet adapter, 1.5 A backplane power, for distributed I/O nodes.
• 1794-ACNR15: FLEX I/O ControlNet adapter, redundant media, 1.5 A backplane power.

Sourcing Hard-to-Find & Obsolete ControlNet Parts

DriveKNMS maintains a dedicated inventory of Allen-Bradley ControlNet components, including physical media (1786-series taps, cables, terminators) and scanner/bridge modules (1756-CNB, 1756-CNBR, 1756-CN2, 1756-CN2R) that are no longer in active production or have been placed on RFQ availability review by Rockwell Automation.

Quality Control for the ControlNet Range

ControlNet modules present specific test challenges due to their integrated backplane communication logic and dual-channel coaxial media interfaces. DriveKNMS applies the following test protocol to all ControlNet modules prior to dispatch:

• Network Update Time (NUT) verification: Each scanner and bridge module is configured in a live ControlNet segment and verified to maintain scheduled connections at the rated NUT without packet loss.
• Dual-channel media integrity test: For redundant modules (1756-CNBR, 1756-CN2R, 1794-ACNR15), both Channel A and Channel B are independently tested for signal integrity and automatic failover response.
• Backplane communication test: Modules are seated in a 1756 ControlLogix chassis and verified for correct I/O tree enumeration and tag data exchange with a test controller.
• Physical media inspection: All 1786-series T-taps and coaxial connectors are inspected for center-pin integrity, dielectric condition, and BNC/N-type connector torque specification compliance.
• Firmware revision audit: Module firmware is documented and, where applicable, updated to the latest Rockwell-approved revision prior to shipment.