Allen-Bradley 1785-ENET PLC-5 Ethernet Sidecar Adapter Module

Description

Product Introduction

The Allen-Bradley 1785-ENET is a specialized Ethernet “sidecar” module designed to add TCP/IP network capabilities to standard classic and enhanced PLC-5 processors (such as the PLC-5/11, PLC-5/20, PLC-5/30, PLC-5/40, PLC-5/60, and /80). By bolting directly onto the left side of the controller, it provides a high-speed communication path without consuming a standard 1771 I/O chassis slot.

Equipped with both a standard RJ45 10Base-T port and a 15-pin AUI connector, the 1785-ENET allows older systems to perform peer-to-peer MSG messaging, SCADA data collection, and program upload/download over standard office/plant Ethernet cabling—eliminating the need to replace existing non-Ethernet CPUs with costly “E” variants (e.g., /40E).

Key Technical Specifications

Application Scenarios & The “Trench” Experience

The Trench Story

A chemical processing plant running a non-Ethernet /40 needs to bridge its batch logging data to an Enterprise MES system. Previously, data was polled slowly over a 57.6k DH+ twinax loop via a 1784-PKTX card, causing severe bottlenecking and dropped transactions during peak production. Instead of replacing the /40 processor (which would require re-keying memory structures and buying expensive “E-suffixed” CPU hardware), technicians bolt a 1785-ENET sidecar onto the existing CPU. Connecting the RJ45 port to the local industrial switch immediately boosts program monitoring and SCADA throughput to 10 Mbps, clearing data backlogs instantly.

Specific Applications

• Modernizing Legacy Systems: Adds Ethernet connectivity to standard CPUs without replacing working processor hardware.
• SCADA & HMI Integration: Enables OPC servers, FactoryTalk View, or Wonderware nodes to poll register data directly over plant LANs.
• Peer-to-Peer Controller Messaging: Executes Ethernet MSG instructions between processors and ControlLogix (1756-EN2T) or CompactLogix systems.
• Remote Programming Access: Allows engineers to upload, download, and debug ladder logic remotely using RSLinx Classic over TCP/IP.

1785-ENET

1785-ENET

Transparency SOP: Quality Assurance & Testing

Every 1785-ENET sidecar module undergoes full physical integration and network communication testing prior to stock placement:

1. Connector & Pins Audit: We clean and inspect the high-density sidecar bus connector pins that mate with the host CPU to ensure zero bent or corroded contacts.
2. Physical Mating Test: The module is physically mounted to a reference /40 CPU in a 1771-A2B rack to verify chassis latching and ground integrity.
3. BOOTP & IP Assignment Test: We verify that the sidecar responds to BOOTP/DHCP requests and accepts static IP address assignment in RSLinx.
4. Active Ethernet Ping & MSG Loopback: Continuous 10 Mbps TCP/IP ping tests and ladder logic Block Transfer/MSG data exchanges are run for two hours to ensure zero packet loss or transceiver overheating.
5. Port Inspection: Both the RJ45 port pins and 15-pin AUI transceiver connectors are tested for mechanical fit and signal continuity.

The Veteran’s Tech Trap Guide

• ⚠️ Half-Duplex 10 Mbps Speed Limit: The 1785-ENET is a legacy 10Base-T (10 Mbps, Half-Duplex) module. Modern managed Gigabit network switches must have their port speed and duplex forced to 10 Mbps / Half-Duplex or set to Auto-Negotiate with speed restriction. Leaving the switch port set to fixed 100/1000 Mbps Full-Duplex will cause complete communication failure.
• ❗ Requires Series & Firmware Compatibility: The 1785-ENET sidecar requires enhanced processors running compatible firmware revisions (typically Series C or later). Always check your firmware revision before installing a sidecar module.
• ⚠️ Power Down the Rack Before Mating: Never attach or detach the 1785-ENET sidecar while 120VAC power is applied to the 1771 rack power supply (e.g., 1771-P7). Hot-plugging the sidecar bus connector can permanently damage the processor’s main logic board.
• ❗ BOOTP Server Tool Required for Initial Setup: Out of the box or after a full reset, the 1785-ENET defaults to BOOTP/DHCP mode. You must use Rockwell’s BOOTP/DHCP Server Utility to set the initial static IP address, Subnet Mask, and Gateway.

Frequently Asked Questions

Q: What is the difference between a /40 with a 1785-ENET and a /40E?

The has an integrated 10Base-T Ethernet port built directly into the front face of the processor. The /40 + 1785-ENET uses a standard non-Ethernet processor combined with an external bolt-on sidecar module to achieve the exact same Ethernet network functionality.

Q: How does the 1785-ENET mount to the processor?

It latches directly to the left side of the processor, connecting via an internal multi-pin sidecar bus interface. It does not occupy a slot on the 1771 I/O chassis backplane.

Q: Which cable connects to the 1785-ENET module?

You can connect a standard RJ45 Ethernet patch cable (Cat5/Cat5e/Cat6) directly to the 10Base-T port, or use an AUI transceiver on the 15-pin port.

Q: Can I communicate with ControlLogix processors using the 1785-ENET?

Yes. The 1785-ENET supports Ethernet MSG instructions and CSPv4/PCCC protocol encapsulation, allowing seamless messaging to ControlLogix controllers equipped with 1756-ENBT or 1756-EN2T cards.

Q: What warranty covers your surplus and refurbished 1785-ENET modules?

Every 1785-ENET sidecar module we ship includes our full 12-month replacement warranty. If a hardware fault or network communication failure occurs under normal operating conditions within 365 days of purchase, we replace the unit immediately from stock or issue a full refund.