Allen-Bradley 1785-L20E PLC-5/20E Ethernet Processor Controller Module

Technical Overview

The Allen-Bradley 1785-L20E belongs to the renowned PLC-5 family, functioning as a high-performance central processing unit for medium-scale industrial control. This single-slot module installs directly into 1771-A1B through 1771-A4B chassis systems, where it manages complex automation tasks with precision. Because it integrates an onboard Ethernet port, this controller enables high-speed data exchange and seamless connectivity across plant-wide networks. Consequently, engineers utilize the 1785-L20E to bridge the gap between legacy Data Highway Plus (DH+) architectures and modern industrial Ethernet environments.

Performance and Memory Capacity

The 1785-L20E features 16,000 words of volatile SRAM memory, which maintains critical logic data via a 1785-XYC lithium battery during power interruptions. To further safeguard operational uptime, the system supports various non-volatile EEPROM modules ranging from 16K to 100K words. Furthermore, the processor manages an expansive I/O image of up to 512 points. This capacity allows the module to orchestrate a local chassis along with up to twelve remote I/O racks. By utilizing fast scan times—reaching 3 milliseconds at 230.4 kbps—the controller ensures rapid response for high-speed manufacturing applications.

Communication and Connectivity

Connectivity remains a core strength of the 1785-L20E. The module provides a comprehensive suite of ports to facilitate multi-layered communication:

• 10/100 Mbps Ethernet port for high-speed messaging and programming
• Dedicated Data Highway Plus (DH+) port for peer-to-peer networking
• Universal Remote I/O (Scanner or Adapter mode) combination port
• Configurable Serial port supporting RS-232, RS-422A, and RS-423 standards

Environmental and Physical Specifications

• Manufacturer: Allen-Bradley / Rockwell Automation
• Series: PLC-5 (Classic and Enhanced)
• Memory: 16K Words (Volatile)
• Max I/O Capacity: 512 Mixed I/O Points
• Operating Temperature: 0 to 60°C (32 to 140°F)
• Vibration Resistance: 1G at 10-500 Hz
• Physical Dimensions: 4.8cm x 15cm x 27.3cm
• Weight: 1.18 kg