Product Overview

The 1785-PFB is a high-performance communication interface designed to bridge Allen-Bradley PLC-5 controller systems with Profibus DP networks. This module serves as a critical gateway, allowing Rockwell Automation hardware to interact seamlessly with a wide array of field devices, remote I/O, and third-party equipment that utilize the Profibus protocol.

A primary advantage of the 1785-PFB is its flexible architecture. It can be software-configured to operate in either a DP Master or a DP Slave capacity. As a Master, it coordinates data exchange across the network, managing addresses and bus parameters for connected slaves. In Slave mode, it allows the PLC-5 to function as a peripheral device to another primary controller. This dual-role capability is essential for facilities integrating multi-vendor hardware into a unified control strategy.

Installation and System Maintenance

The 1785-PFB installs directly into a 1771 I/O chassis, drawing power through the backplane. To protect the sensitive surface-mount electronics, it is imperative that the module is only inserted or removed when the chassis power is completely disconnected. Failure to follow "cold-swap" procedures can result in terminal damage to the communication ports or the backplane interface.

Despite its legacy status, the 1785-PFB remains a cornerstone for maintaining and expanding existing PLC-5 installations. It provides a cost-effective alternative to full system migrations by allowing older processors to communicate with modern Profibus-enabled drives, sensors, and actuators.

Technical Specifications

• Module Type: Profibus DP Communication Gateway

• Protocol Support: Profibus DP (Decentralized Peripherals)

• Processor Compatibility: Allen-Bradley PLC-5 Series

• Data Rates: Supports standard Profibus baud rates (9.6 Kbps to 12 Mbps)

• Network Interface: 9-pin D-shell (RS-485)

• Configuration Port: RS-232 Serial

• Backplane Current Load: 1.0 Amp @ 5V DC

• Maximum Slaves Supported: Up to 125 (as a Master)

• Status Indicators: LED diagnostics for module health and network activity

• Operating Temperature: 0°C to 60°C (32°F to 140°F)

• Weight: 720g

• Dimensions: 4.1 x 18.8 x 26.2 cm
  

Core Functions and Use Cases

• Multi-Vendor Interoperability: Enabling PLC-5 controllers to command Siemens, ABB, or Danfoss variable frequency drives (VFDs).

• Distributed Network Control: Managing remote I/O blocks across large distances via the robust RS-485 physical layer.

• Process Modernization: Integrating new analytical instrumentation into legacy PLC architectures without replacing the main CPU.

• Data Concentration: Serving as a slave device to higher-level SCADA systems or master controllers for centralized monitoring.