Allen-Bradley 1785-PFB – PROFIBUS-DP Master/Slave Communication Module | PLC-5 Series Platform
Engineering Background
The Allen-Bradley 1785-PFB is a dedicated PROFIBUS-DP communication interface module designed for integration into the PLC-5 programmable controller platform. Developed by Rockwell Automation to address the growing demand for open fieldbus connectivity in process and discrete manufacturing environments, this module enables PLC-5 processors to act as PROFIBUS-DP Class 1 Masters or Slaves on a multi-drop RS-485 network — bridging legacy Allen-Bradley control infrastructure with modern distributed I/O architectures.
Product Positioning
The 1785-PFB occupies a critical role in brownfield automation projects where PLC-5 controllers remain the backbone of production lines but must communicate with PROFIBUS-enabled field devices such as variable frequency drives, remote I/O stations, smart sensors, and third-party PLCs. It is the preferred solution for engineers who need to extend the service life of existing PLC-5 installations without a full controller migration.
Complete Technical Specifications
- Part Number: 1785-PFB
- Manufacturer: Allen-Bradley / Rockwell Automation
- Platform Compatibility: PLC-5 Family (PLC-5/11, 5/20, 5/30, 5/40, 5/60, 5/80)
- Fieldbus Protocol: PROFIBUS-DP (EN 50170 / IEC 61158)
- Node Role: Class 1 DP Master or DP Slave (configurable)
- Max Baud Rate: 12 Mbps
- Max Slave Nodes: 125 per segment (with repeaters)
- Physical Interface: DB-9 female connector (RS-485)
- Backplane Interface: PLC-5 I/O chassis slot
- Power Consumption: Supplied via PLC-5 backplane
- Operating Temperature: 0 °C to +60 °C
- Storage Temperature: -40 °C to +85 °C
- Relative Humidity: 5% to 95% non-condensing
- Weight: Approx. 80 g
- Certifications: UL, CE (refer to Rockwell publication 1785-UM052)
- Configuration Tool: RSNetWorx for PROFIBUS
Proven Application Environments
- Automotive Assembly: Coordinating robot controllers and conveyor drives via PROFIBUS-DP from a PLC-5 master
- Oil & Gas: Integrating remote valve actuators and flow transmitters on PROFIBUS segments supervised by PLC-5 systems
- Water & Wastewater: Connecting distributed pump drives and level sensors across large plant footprints
- Food & Beverage: Synchronizing filling lines with PROFIBUS-enabled weighing and dosing equipment
- Pharmaceutical: Interfacing with PROFIBUS-DP compliant batch reactors and CIP skids under PLC-5 supervisory control
- Power Generation: Monitoring and controlling auxiliary systems via PROFIBUS from legacy PLC-5 controllers
Engineering Advantages
- Open Fieldbus Standard: Full compliance with EN 50170 / IEC 61158 ensures interoperability with any certified PROFIBUS-DP device regardless of manufacturer
- High-Speed Communication: Supports baud rates up to 12 Mbps, enabling deterministic, low-latency I/O updates across the fieldbus segment
- Dual Role Flexibility: Configurable as Master or Slave, allowing integration into both standalone PLC-5 control architectures and larger PROFIBUS networks supervised by a DCS or SCADA system
- Brownfield Investment Protection: Extends the operational life of PLC-5 platforms by adding modern fieldbus capability without requiring controller replacement
- Diagnostic Transparency: Provides per-slave diagnostic data accessible via the PLC-5 data table, enabling proactive fault detection and reduced unplanned downtime
- Proven Reliability: Field-proven in harsh industrial environments with a robust hardware design consistent with Allen-Bradley’s PLC-5 series quality standards
System Architecture & Signal Flow
The 1785-PFB module is installed in any available slot of a PLC-5 I/O chassis. The PLC-5 processor communicates with the module via the backplane using block-transfer read/write (BTR/BTW) instructions. The module’s onboard PROFIBUS-DP controller manages the cyclic exchange of process data (I/O images) and acyclic parameter/diagnostic data with up to 125 slave nodes on the RS-485 segment. Configuration is performed offline using RSNetWorx for PROFIBUS, which generates a GSD-based network configuration downloaded to the module. During runtime, the PLC-5 ladder logic program maps PROFIBUS slave I/O data directly into the PLC data table for use in control logic.
Signal Flow Summary: PLC-5 Processor ↔ Backplane BTR/BTW ↔ 1785-PFB Module ↔ RS-485 PROFIBUS-DP Segment ↔ Field Devices (Drives, Remote I/O, Sensors, Actuators)
Sourcing & Quality Verification
- Stock Origin: Genuine Allen-Bradley / Rockwell Automation surplus and refurbished units sourced from verified industrial decommissioning projects and authorized distribution channels
- Inspection Protocol: Each unit undergoes visual inspection, firmware version verification, and functional power-on testing prior to listing
- Authenticity Guarantee: Konmask.com does not deal in counterfeit or unauthorized reproduction parts — all units are traceable to legitimate industrial sources
- Packaging: Anti-static ESD packaging with protective foam insert; shipped in reinforced carton
- Warranty: 90-day functional warranty against defects in materials and workmanship
Procurement Process
- Confirm Compatibility: Verify your PLC-5 chassis model and available slot count; confirm PROFIBUS-DP network topology and baud rate requirements
- Request Quote: Contact support@konmask.com with your required quantity and delivery timeline for volume pricing
- Place Order: Add to cart and complete checkout, or submit a purchase order via email for B2B net-term arrangements
- Shipping: Orders dispatched within 1–3 business days; DHL / FedEx international express available; lead time confirmed at order
- Technical Onboarding: Our engineering team provides post-purchase configuration guidance including RSNetWorx setup assistance upon request
Technical FAQ
Q: Is the 1785-PFB compatible with all PLC-5 processor variants?
A: The module is compatible with PLC-5/11, 5/20, 5/30, 5/40, 5/60, and 5/80 processors. It is not compatible with SLC 500 or ControlLogix platforms — for those, refer to the 1747-PIC or 1784-PKTX respectively.
Q: Can the 1785-PFB operate as both Master and Slave simultaneously?
A: No. The module operates in one role at a time — either as a DP Master or DP Slave — as configured via RSNetWorx for PROFIBUS.
Q: What GSD file is required for third-party PROFIBUS masters to recognize the 1785-PFB as a slave?
A: The GSD file is available from Rockwell Automation’s product compatibility and download center (PCDC). Contact Konmask support for assistance locating the correct file version.
Q: What is the maximum cable length per PROFIBUS-DP segment?
A: At 12 Mbps, maximum segment length is 100 m. At 1.5 Mbps, up to 200 m. At 93.75 kbps, up to 1200 m. Repeaters can extend total network reach.
Q: Does Konmask provide a test report or inspection certificate?
A: Yes. A functional test report is available upon request for orders of 2 or more units. Contact support@konmask.com.
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