Overview
The Allen-Bradley 1785-L86B is a PLC-5/86 processor module from Rockwell Automation, engineered for integration into 1771 I/O chassis-based automation systems. As a member of the enhanced PLC-5 family with protected memory capability, this single-slot processor delivers high-speed control with advanced memory security features. It is widely deployed in legacy manufacturing, process control, and critical infrastructure applications where system uptime and restricted program access are essential.
Key Features
- Protected Memory Architecture: Limits access to critical program and data words, supporting custom security policies for proprietary applications and multi-user environments.
- 100K Words User Memory: Expandable via 1785-ME16, ME32, or ME64 memory modules for larger programs and data logging requirements.
- High I/O Capacity: Supports up to 3072 analog I/O points or 3072 inputs + 3072 outputs in complementary digital mode with single 1771 chassis slot.
- Dual Communication Modes: Four configurable ports for Data Highway Plus (DH+) messaging or Remote I/O (RIO) real-time I/O scanning, enabling peer-to-peer device communication and distributed I/O architectures.
- Integrated Battery-Backed SRAM: Retains user program and data during power loss, eliminating need for external memory backup modules.
- Multiple Programming Languages: Supports Ladder Logic (LAD), Sequential Function Charts (SFC), and Structured Text (ST) via RSLogix 5 and Rockwell Software suite.
Technical Specifications
Memory & Processing:
- User Program Memory: 100,000 words maximum (embedded SRAM)
- Memory Type: Battery-backed static RAM (SRAM) with protected segments
- I/O Capacity: 3072 maximum analog I/O or 3072 digital inputs + 3072 outputs in complementary mode
Communication Ports:
- DH+ Ports: Up to 4 channels (Data Highway Plus/Remote I/O capable)
- Remote I/O: Supports 93 chassis links with 32 remote chassis per link, up to 24 I/O racks
- Relay Cartridge Interface: Compatible with 1785-RC for external device integration
Power & Environmental:
- Backplane Current: 3.3 A at 5 V DC
- Heat Dissipation: 17.3 W during normal operation
- Operating Temperature: 0 to 60 °C (32 to 140 °F) at 5–95% relative humidity (non-condensing)
- Storage Temperature: –40 to 85 °C (–40 to 185 °F)
- Vibration Tolerance: 2 G at 10–500 Hz
- Shock Tolerance: 30 G operational
Certifications & Safety:
- Voltage Isolation: 500 V for 60 seconds (communication ports to chassis); 300 V for 60 seconds (relay cartridge)
- Standards: UL, CSA, C-TICK, CE compliant
- Weight: Approximately 1.42 kg (3.13 lbs)
Typical Applications
- Discrete manufacturing control (automotive, packaged goods, assembly lines)
- Batch and process control in food, beverage, and chemical plants
- Legacy system modernization and replacement when original processors fail
- Distributed remote I/O scanning over Data Highway Plus networks
- Security-critical applications requiring program memory protection and multi-level user privileges
- Systems with mixed 1771 I/O modules (analog, digital, specialty) in local and remote configurations
Compatibility & Replacements
The 1785-L86B is the protected-memory equivalent of the standard 1785-L80B (PLC-5/80) processor. Both models offer identical I/O capacity and memory size but differ in access control capabilities. This module integrates into any 1771-based chassis and is compatible with all 1771 I/O modules (8-point, 16-point, 32-point, and intelligent modules). Memory can be expanded using the 1785-ME16, 1785-ME32, or 1785-ME64 modules. For systems requiring Ethernet connectivity, consider the 1785-L80E or 1785-L20E (which support EtherNet/IP with DH+ ports). ControlNet-capable variants include the 1785-L46C15 (48K memory) and 1785-L80C15 (100K memory). Original programming is created and maintained using RSLogix 5 software and Rockwell Automation development tools.
