Product Overview

The 1785-LT3 is a high-performance central processing unit belonging to the Allen-Bradley PLC-5® Classic family. Engineered for reliable discrete and process control, this processor provides a total capacity of 512 I/O points and features 6K words of internal memory. It is specifically designed to function as a robust controller in legacy automation architectures, supporting advanced instruction sets for complex logic, mathematical operations, and data management.

The module is equipped with a dedicated Data Highway Plus (DH+) channel, which serves as the primary interface for peer-to-peer communication, remote programming, and plant-floor data acquisition. Additionally, the 1785-LT3 includes a Remote I/O (RIO) adapter port, allowing it to function efficiently within a larger distributed control network. Its architecture is optimized for high-speed logic execution and is compatible with Sequential Function Chart (SFC) programming to simplify the management of multi-step industrial processes.

Technical Specifications

• Manufacturer: Allen-Bradley / Rockwell Automation

• Model Number: 1785-LT3

• Product Series: PLC-5

• Memory Capacity: 6,000 (6K) Words

• Total I/O Capacity: 512 Max

• Backplane Current Load: 2.5A @ 5V DC

• Communication Interfaces: DH+ (Data Highway Plus) and RIO (Remote I/O Adapter)

• RIO Transmission Rate: 57.6 kbps

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

• Storage Temperature: -40 to 85°C (-40 to 185°F)

• Weight: 1.44 kg

• Dimensions: 4.6 cm x 16.0 cm x 27.4 cm

Core Functionality and Communication

The 1785-LT3 facilitates seamless integration across the factory floor by connecting up to 64 stations on a single DH+ link. This capability allows engineers to perform remote diagnostics, program uploads/downloads, and real-time monitoring from a centralized workstation. The inclusion of a Control Coprocessor Expansion Port further enhances its versatility, enabling the addition of specialized modules for expanded computational power or specific communication protocols.

Built to withstand the rigors of industrial environments, the processor maintains high-speed performance even in high-vibration and temperature-variant settings. It supports specialized programming features that allow users to test logic in a "Force" or "Remote" mode before full system implementation, reducing the risk of downtime during commissioning.

Application and Legacy Support

As a cornerstone of the PLC-5 platform, the 1785-LT3 is ideal for maintaining and upgrading existing control systems in automotive, food and beverage, and material handling industries. Its mechanical design allows for direct insertion into 1771 I/O chassis, providing a reliable path for sustaining legacy infrastructure with proven, high-reliability hardware.