Overview
The Allen-Bradley 1785-L40B /B is a standard PLC-5/40 processor module engineered for medium to large-scale industrial automation and control systems. It features 48K words of memory and provides deterministic ladder-logic control for manufacturing, motion, and process applications. As a legacy PLC-5 series processor, it maintains compatibility with the extensive 1771-series I/O chassis and mixed discrete/analog I/O configurations.
Key Features
- 48K words of user memory supporting 2048 total I/O (any mix) or 2048 input + 2048 output configurations
- Four DH+ ports supporting mode selection between network adapter and scanner modes, plus universal remote I/O
- One serial port configurable for RS-232, RS-423, and RS-422A communication standards
- Support for optional EEPROM backup memory modules (1785-ME16, 1785-ME32, 1785-ME64, 1785-ME100) for non-volatile program storage
- Capability to support up to 29 PLC-5 racks (1 local + 28 remote I/O racks)
- Battery-backed static RAM for program retention during power loss
Technical Specifications
The processor includes four combination DH+ or Remote I/O (Adapter or Scanner) ports and one serial port, each capable of supporting independent networks. The serial communication channel provides point-to-point interface for short-distance communication.
Typical Applications
The 1785-L40B /B suits applications requiring:
- Medium to large distributed control systems with multiple I/O racks
- Mixed analog and discrete control with up to 2048 I/O addressing
- Legacy PLC-5 system upgrades and replacements
- Manufacturing automation requiring four independent communication networks
- Systems needing deterministic real-time control and ladder-logic programming
Compatibility & Replacements
The 1785-L40B /B is part of the legacy PLC-5 series and interfaces with 1771-series I/O modules for discrete, analog, and specialty functions. It is designed for installation in 1771 I/O chassis and offers plug-and-play compatibility with existing PLC-5 automation systems. For systems requiring additional memory, optional companion modules such as the 1785-ME64 (64K words) can be installed alongside the processor. This used unit provides cost-effective control solutions for maintenance and system integration projects where legacy platform continuity is required.
