SKU: 1785-PFB

Allen-Bradley 1785-PFB Profibus Communication Module

The Allen-Bradley 1785-PFB is a Profibus DP communication module designed for the PLC-5 system. It enables 1771-based controllers to interface with Profibus networks at speeds up to 12 Mbps, supporting both Master and Slave configurations for comprehensive multi-vendor device integration.

Technical Overview

The Allen-Bradley 1785-PFB acts as a high-performance communication interface that enables PLC-5 controllers to connect directly to a Profibus DP (Decentralized Periphery) network. This module bridges the gap between Rockwell Automation’s legacy architecture and open-standard industrial fieldbus systems. By installing the 1785-PFB into a PLC-5 1771 I/O chassis, users allow the controller to function as a Profibus DP Master or Slave, facilitating seamless data exchange with a diverse range of third-party devices such as drives, sensors, and remote I/O stations.

Functional Integration and Network Management

This module manages complex network protocols by offloading communication tasks from the main PLC processor. Because the 1785-PFB handles the specific timing and cyclic data exchange requirements of the Profibus standard, it preserves the controller’s scan time for critical logic execution. Furthermore, the unit supports data rates up to 12 Mbps, which ensures high-speed synchronization across the factory floor.

To streamline system setup, the 1785-PFB utilizes a standard 9-pin D-shell sub-miniature connector for network attachment. Consequently, maintenance teams can integrate the module into existing Profibus infrastructures using standard cabling and termination techniques. Since the module fits into any single slot of a 1771 I/O rack, it offers a space-efficient solution for upgrading communication capabilities without requiring significant hardware re-engineering.

Key Technical Characteristics

Manufacturer: Allen-Bradley / Rockwell Automation
Model Identification: 1785-PFB
Module Function: Profibus DP Master/Slave Scanner
Platform Compatibility: PLC-5 Systems (1771 Chassis)
Maximum Baud Rate: 12 Mbps
Connection Port: 9-pin D-sub (RS-485)
Network Capacity: Supports up to 125 Slave devices (in Master mode)
Backplane Current Load: 1.2 A at 5V DC
Configuration Tool: Typically configured via Profibus Configuration Software (Windows-based)

Primary Applications

Connecting PLC-5 controllers to Siemens, ABB, or other third-party Profibus-compatible drives.
Integrating non-Rockwell remote I/O into a centralized Allen-Bradley control system.
Enabling data exchange between heterogeneous PLC platforms in multi-vendor plants.
Modernizing legacy machinery by adding standardized fieldbus communication.