Overview
The Allen-Bradley 1785-L40L is a standard processor from the PLC-5 series designed for medium-scale industrial automation and control systems. Built for installation in a 1771 I/O chassis, this processor provides 48,000 words of user memory with extended local I/O capability, coordinating and controlling field devices across distributed architectures. The 1785-L40L supports communication via Data Highway Plus (DH+), Remote I/O networks, and extended local I/O, making it ideal for legacy systems requiring robust, proven performance.
Key Features
- 48,000 words of SRAM user memory with battery-backed backup capability
- Extended Local I/O port for high-speed communication with local I/O chassis
- Dual DH+/Remote I/O communication channels configurable for adapter or scanner mode
- 1 RS-232/RS-422/RS-423 serial port for legacy device connectivity
- Supports up to 2,048 total I/O points across mixed 8, 16, and 32-point modules
- Manages up to 61 I/O chassis (16 extended local, 32 per universal remote I/O link)
- Fast scan performance: 0.5 ms per rack for extended local I/O
Technical Specifications
- Memory Capacity: 48,000 words (48K) SRAM user memory
- Maximum I/O Points: 2,048 (any mix; 2,048 input + 2,048 output complementary)
- Communication Ports: 2 channels DH+/Remote I/O (Adapter/Scanner), 1 Extended Local I/O port, 1 serial port (RS-232/422/423)
- Maximum I/O Chassis: 61 total (16 extended local, 32 per universal remote link)
- Backplane Current Draw: 3.3 A @ 5V DC
- Heat Dissipation: 17W operational; 65 BTU/hour average
- Operating Temperature: 0–60°C
- Mounting: Slot 1 (leftmost) of 1771 I/O chassis
- Dimensions: 2 × 6 × 11 inches (shipping)
- Weight: 3 lbs 1 oz (1.42 kg)
- Certifications: UL, CE, C-TICK, CSA
Typical Applications
The 1785-L40L excels in food and beverage processing, packaging lines, automotive assembly, water treatment, and general discrete/analog manufacturing. Its 48K memory and extended I/O capability suit systems requiring moderate program complexity with distributed local I/O. Common in legacy upgrade scenarios where direct plug-in replacement is needed.
Compatibility & Replacements
Compatible With
- 1771 I/O chassis (leftmost slot installation required)
- 1771 digital I/O modules (8, 16, 32-point)
- 1771 analog I/O modules
- 1785-RC relay cartridge for external relay interface
- 1770-XYC battery module for memory backup (CSA-certified applications)
- ControlLogix, SLC 500, and MicroLogix controllers via gateway/bridge
- Data Highway Plus (DH+) networks
- Remote I/O adapters and scanners
Replaces / Drop-In Replacement For
Verify compatibility with your system integrator before ordering. The 1785-L40L /A Rev C specification should match the processor currently installed in your 1771 chassis. Processor replacements require memory module transfer or reprogramming.
Works With
- PLC-5 Programming Software (release 4.1 or later)
- Data Highway Plus (DH+) for peer-to-peer communication
- Remote I/O networks (scanner/adapter modes)
- Extended Local I/O adapters for fast local I/O communication
- EtherNet/IP, ControlNet, and DeviceNet networks via gateway modules
- Legacy serial devices via RS-232/422/423 port
