Overview
The Allen-Bradley 1785-L80B Series E Enhanced PLC-5/80 is a central processing unit designed for large-scale industrial automation and motion control systems. This processor module connects local, extended, and remote I/O modules across multiple communication interfaces into a unified control system. With discontinued-by-manufacturer status as of July 2017, the 1785-L80B remains a workhorse in legacy PLC-5 environments and is widely available through industrial surplus and refurbished channels.
Key Features
- 100,000 words of embedded SRAM user memory for large program capacity
- Four built-in DH+ and Remote I/O communication ports (Channels 1A, 1B, 2A, 2B)
- One configurable serial port supporting RS-232, RS-423, and RS-422A protocols
- Supports up to 3,072 I/O points (any mix of analog and digital)
- Two programming terminal ports for local troubleshooting and configuration
- Proven performance in production environments since first release
Technical Specifications
- Model: PLC-5/80 Processor Module
- User Memory: 100,000 words SRAM
- Maximum I/O: 3,072 points (total analog or mixed digital/analog)
- Backplane Current (at 5V): 3.3 Amperes
- Power Dissipation: 17.3 Watts
- Communication Ports: 4 DH+/Remote I/O channels; 1 serial port (25-pin D-shell)
- Serial Port Protocols: DF1, ASCII (point-to-point, master, and slave modes)
- I/O Scan Time (per rack): 10 ms @ 57.6 kbits/s, 7 ms @ 115.2 kbits/s, 3 ms @ 230.4 Mbits/s
- Default DH+ Speed: 57.6 kbps on Channel 1A
- Default Remote I/O Scanner: Channel 1B
- Weight: 3.0 lbs
- Manufacturer Status: Discontinued 07/31/2017
- Series: Enhanced (Series E variant)
Typical Applications
The 1785-L80B is deployed in:
- Large-scale production line automation with multiple remote racks
- Motion control systems requiring high I/O density and multi-network communication
- Facility control and batch processing environments
- Legacy system retrofits and plant modernization projects
- High-speed sequential and discrete process control
Compatibility & Replacements
Compatible With
- PLC-5 platform backplane and chassis
- PLC-5 I/O modules (1771-series analog/digital adapters)
- DH+ networks (up to maximum cable length per transmission rate)
- Remote I/O Scanner configurations
- Programmable controllers and programming terminals
- Factory-standard serial communication (DF1, ASCII protocols)
Replaces / Drop-In Replacement For
- Earlier PLC-5/80 processor modules in legacy PLC-5 systems
- Other Series E 1785-L80B variants (identical functionality across revisions)
Works With
- Allen-Bradley PLC-5 platform software and ladder logic programming
- DF1 protocol (point-to-point, master/slave communication)
- DH+ protocol for networked I/O scanning and remote communication
- RS-232/RS-423/RS-422A serial interfaces
- Legacy HMI and SCADA systems compatible with PLC-5 DH+ networks
