Overview
The Allen-Bradley 1785-L80B is a PLC-5/80 enhanced processor from Rockwell Automation, designed for complex distributed control and large I/O applications. This legacy controller remains widely deployed in manufacturing, process control, and motion systems where DH+ and Remote I/O integration is critical. The 1785-L80B provides 100K words of battery-backed SRAM user memory and multi-channel communication capability for centralized or distributed architectures.
Key Features
- 100K word (100,000 word) embedded battery-backed SRAM user memory
- Four (4) configurable DH+/Remote I/O channels (1A, 1B, 2A, 2B)
- Supports up to 3,072 I/O points (mixed or complementary mode: 3,072 inputs + 3,072 outputs)
- Serial port (Channel 0) with DF1 full/half-duplex and ASCII protocol support; RS-232, RS-422A, RS-423 compatible
- Two (2) programming terminals for offline development
- Remote I/O scanner and adapter modes for flexible network topology
- Ladder logic and structured text programming support
- 3.3 Amperes backplane current draw at 5V; 17.3 Watts heat dissipation
Technical Specifications
| Processor Type | PLC-5/80 Enhanced Processor |
| User Memory | 100 Kilowords (100,000 words) embedded SRAM |
| Memory Type | Battery-backed static RAM (SRAM) |
| Maximum I/O | 3,072 total mixed or 3,072 inputs + 3,072 outputs (complementary) |
| Analog I/O Support | Up to 3,072 analog points |
| DH+ Channels | 4 channels (1A, 1B, 2A, 2B) – configurable as Remote I/O scanner or adapter |
| Serial Port (Ch 0) | 25-pin D-sub; DF1, ASCII protocols; RS-232/RS-422A/RS-423 |
| I/O Scan Time | 10 ms @ 57.6 kbits/s; 7 ms @ 115.2 kbits/s; 3 ms @ 230.4 kbits/s |
| Backplane Current | 3.3 Amperes @ 5VDC |
| Power Dissipation | 17.3 Watts |
| Memory Expansion | Optional modules: 1785-ME16, 1785-ME32, 1785-ME64 |
| Series | Enhanced PLC-5 (Series E) |
| Condition | Used |
Typical Applications
- Large discrete and process manufacturing lines requiring distributed I/O control
- Multi-node DH+ networks connecting remote I/O stations and operator interfaces
- Legacy system upgrades and maintenance when additional memory or channel capacity is needed
- Centralized control of 93+ I/O chassis and up to 32 Remote I/O racks
- Retrofit projects in automotive, food & beverage, chemical, and packaging industries
Compatibility & Replacements
The 1785-L80B is part of the PLC-5 legacy line and programmed via Rockwell’s RSLogixâ„¢ 5 software. Older PLC-5 models like the 1785-L80 (standard, non-enhanced) lack the Series E improvements and reduced I/O capacity. The 1785-L50 and 1785-L60 offer lower memory but remain software-compatible. There is no direct CompactLogix or ControlLogix drop-in replacement; migrations typically require reprogramming. The 1785-ME16, 1785-ME32, and 1785-ME64 memory modules expand embedded storage. For modern Ethernet networks, the EtherNet/IP-enabled PLC-5/80E (1785-L80E) provides gateway capability but is a separate SKU. Used 1785-L80B units remain in stock from multiple distributors for maintenance and emergency repair scenarios.
