Allen-Bradley 1785-BEM Industrial Network Interface for PLC-5 Systems
The Allen-Bradley 1785-BEM Backup Communications Expansion Module is a purpose-built industrial network interface designed to extend and reinforce the data communication backbone of PLC-5 Series control systems. In modern smart factory environments where uninterrupted data flow between field devices, controllers, remote I/O racks, HMI panels, and SCADA platforms is mission-critical, the 1785-BEM delivers the protocol reliability and network redundancy that production lines demand. Whether deployed in automotive assembly, chemical processing, water treatment, or discrete manufacturing, this module ensures that your PLC-5 system remains fully connected across the entire automation data chain.
At its core, the 1785-BEM supports Data Highway Plus (DH+) and Remote I/O (RIO) protocols — two foundational communication standards in Rockwell Automation’s legacy and hybrid control architectures. By functioning as a backup communications expansion module, it provides a secondary communication path that activates seamlessly when the primary link encounters a fault, eliminating single points of failure in your network topology. This redundancy is especially critical in continuous-process industries where even a brief communication dropout can trigger costly production stoppages or safety incidents.
Network Communication Table
| Parameter |
Specification |
| Supported Protocols |
Data Highway Plus (DH+), Remote I/O (RIO) |
| Interface Type |
Backplane expansion module (PLC-5 rack-mount) |
| Transmission Capability |
Backup communication path with automatic failover |
| Network Compatibility |
Allen-Bradley PLC-5 Series, ControlLogix (via bridge), SLC 500 (via gateway) |
| System Application |
DCS integration, SCADA connectivity, Remote I/O expansion, HMI data link |
| Operating Environment |
Industrial panel, control cabinet, harsh environment rated |
| Warranty |
12-Month Warranty — tested and verified before shipment |
Connected Automation Data Flow
In a fully integrated smart factory, the 1785-BEM sits at the heart of the communication architecture, bridging field-level signals with supervisory control systems. Consider a typical production line where a 1785-L40B PLC-5/40 processor manages multiple remote I/O drops via a 1771-ASB Remote I/O Adapter. The 1785-BEM provides the backup DH+ link that keeps the processor in continuous communication with operator workstations running RSView32 SCADA software, ensuring that production data — cycle counts, alarm states, energy readings — flows without interruption to the control room.
Further upstream, a 1784-PKTXD PCI Communication Card installed in the engineering workstation enables programming and diagnostics over the DH+ network, allowing maintenance engineers to monitor ladder logic execution and I/O status in real time without interrupting production. When the primary communication path is occupied or degraded, the 1785-BEM’s backup channel takes over transparently, maintaining the data link between the PLC-5 processor and connected 1771-OBD DC Output Modules and 1771-IBD DC Input Modules across the I/O chassis.
For facilities that are migrating toward EtherNet/IP-based architectures, the 1785-BEM can be paired with a 1761-NET-ENI Serial-to-Ethernet Interface or a 1788-EN2DN EtherNet/IP-to-DeviceNet Linking Device to bridge legacy DH+ segments with modern Ethernet infrastructure. This allows SCADA systems built on FactoryTalk View SE to pull real-time data from PLC-5 controllers without requiring a full system replacement, protecting capital investment while enabling incremental modernization.
On the drive side, PowerFlex 700 AC drives connected via Remote I/O to the PLC-5 system rely on stable, low-latency communication to receive speed references and return feedback data. The 1785-BEM ensures that this drive-to-controller data path remains active even during primary network maintenance windows, preventing unplanned motor stops on conveyor systems, pump stations, or compressor banks. Similarly, PanelView 600 HMI terminals connected over DH+ continue to display live process data and accept operator inputs without interruption.
For remote diagnostic capability, the 1785-BEM’s network redundancy supports integration with FactoryTalk AssetCentre for audit trail logging and remote access, enabling plant engineers to diagnose communication faults, review historical alarm data, and push configuration updates from a central location — a key requirement for multi-site industrial operations seeking to reduce on-site maintenance visits and associated downtime costs.
Solving Data Isolation in Industrial Sites
One of the most persistent challenges in legacy industrial environments is data isolation — the condition where field devices, controllers, and supervisory systems operate in disconnected silos, making it impossible to achieve real-time production visibility or implement predictive maintenance strategies. The 1785-BEM directly addresses this challenge by providing a reliable, redundant communication backbone that keeps PLC-5 systems continuously connected to the broader automation network.
In facilities where protocol fragmentation is common — with DH+ segments serving older PLC-5 and SLC 500 controllers alongside newer EtherNet/IP devices — the 1785-BEM acts as a stabilizing anchor for the legacy network layer. By maintaining a backup DH+ path, it prevents the communication failures that typically cause data gaps in historian databases, missed alarm notifications in SCADA systems, and delayed responses from HMI operators. This directly improves production line transparency, giving plant managers accurate, real-time data on equipment status, cycle times, and fault histories.
For remote monitoring applications, the 1785-BEM’s network redundancy enables continuous data streaming to edge gateways and cloud-based analytics platforms, supporting predictive maintenance models that rely on uninterrupted data feeds. Plants that have deployed the 1785-BEM as part of their communication redundancy strategy report measurable reductions in unplanned downtime, with backup communication failover occurring in milliseconds — fast enough to be invisible to connected HMI and SCADA systems.
System expansion is equally straightforward. As production lines grow and additional Remote I/O drops, drive nodes, or sensor networks are added to the DH+ segment, the 1785-BEM scales with the architecture without requiring changes to the primary communication configuration. This makes it an ideal long-term investment for facilities that need to expand capacity incrementally while maintaining network stability across the entire control system.
Every 1785-BEM unit shipped by ZYPLC undergoes full functional testing prior to dispatch, verifying DH+ communication integrity, backplane interface operation, and failover response. Units are available from stock for immediate shipment via DHL or FedEx, with a 12-month warranty covering all hardware defects and communication failures.
Industrial Connectivity FAQ
Q: What communication protocols does the 1785-BEM support, and is it compatible with EtherNet/IP networks?
A: The 1785-BEM natively supports Data Highway Plus (DH+) and Remote I/O (RIO) protocols. It does not natively support EtherNet/IP, but can be integrated into EtherNet/IP architectures using bridging devices such as the 1761-NET-ENI or ControlLogix gateway processors, allowing legacy PLC-5 systems to exchange data with modern EtherNet/IP-based SCADA and MES platforms.
Q: How quickly does the 1785-BEM switch to the backup communication path during a primary link failure?
A: Failover to the backup DH+ communication path managed by the 1785-BEM occurs in milliseconds, ensuring that connected HMI terminals, SCADA systems, and Remote I/O devices experience no perceptible data interruption. The switchover is transparent to the PLC-5 processor and does not require a controller restart or program modification.
Q: Can the 1785-BEM be used to expand an existing PLC-5 network with additional Remote I/O drops or communication nodes?
A: Yes. The 1785-BEM supports network expansion by providing an additional DH+ communication path that can accommodate new Remote I/O adapters, drive nodes, and HMI connections without disrupting the existing primary network configuration. This makes it suitable for phased production line expansions where new equipment must be integrated without taking the existing system offline.
Q: What testing and warranty coverage does ZYPLC provide for the 1785-BEM?
A: Every 1785-BEM unit is fully tested before shipment, including DH+ protocol communication verification, backplane interface integrity checks, and failover response validation. All units are covered by a 12-month warranty against hardware defects and communication failures. ZYPLC maintains stock inventory for immediate dispatch, with global shipping via DHL and FedEx to minimize lead times for urgent replacement requirements.
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