Allen-Bradley 1785-LT2 PLC-5 Processor Module

Overview

The 1785-LT2 from Allen-Bradley is a high-performance processor module within the PLC-5 Classic series, designed for versatile industrial control applications. It supports extensive local and remote I/O configurations and provides embedded communication channels including Data Highway Plus (DH+) and RS-232. This module is mounted in the left-most slot of a 1771 I/O chassis and delivers reliable control for medium-to-large automation systems.

Technical Specifications

• Manufacturer: Allen-Bradley

• Product Line: PLC-5 Classic

• Part Number: 1785-LT2

• Module Type: Processor

• Supported Local I/O: Up to 4 racks (1 resident rack)

• Supported Remote I/O: Up to 3 remote racks

• Total I/O Capacity: 512 inputs / 512 outputs (expandable with modules)

• Maximum Total I/O: 3072 points (any mix)

• Analog I/O: Up to 3072 points

• Embedded RAM: 6K Words (expandable to 14K Words)

• Memory Modules Supported: 1785-MR (4K RAM), 1785-MS (8K RAM), 1785-MJ (8K EEPROM)

• Battery: 1770-XY

• Program Scan Time: 2 ms per K words (bit logic), 8 ms per K words (typical)

• Built-in Communication: One DH+ channel, one local/remote I/O scanner adapter

• Hardware Addressing: 2-slot, 1-slot, ½ slot

• Control Coprocessor Expansion: Supported

• RS-232-C/422-A/423-A Ports: 1

Performance & Communication

• I/O Scan Time per Rack:

• 10 ms @ 57.6 kbits/s

• 7 ms @ 115.2 kbits/s

• 3 ms @ 230.4 kbits/s

• Maximum I/O Chassis Total: 93

• Max Extended Local Chassis: 0

• Max Universal Remote Chassis: 32 per I/O Link

Installation & Mounting

• Location: Left-most slot in 1771 I/O chassis

• Module Keying: Between 40–42 and 54–56

• Weight: 3.06 lbs (1.39 kg)

Applications

• Industrial automation requiring scalable I/O control

• Medium to large PLC-5 system integration

• Remote I/O management with high-speed DH+ communication

• Analog and digital I/O intensive processes

FAQ

Q: Can 1785-LT2 support remote I/O racks?
A: Yes, up to 3 remote racks are supported.

Q: What memory expansion options are available?
A: Supports 4K, 8K RAM modules (1785-MR, 1785-MS) and 8K EEPROM (1785-MJ).

Q: What communication channels are built-in?
A: Includes one DH+ port and one local/remote I/O scanner adapter.