Overview
The Allen-Bradley 1785-L20E Series E is a proven PLC-5/20 Ethernet processor designed for industrial automation applications requiring network connectivity and reliable logic control. This processor combines battery-backed SRAM memory with embedded EtherNet/IP communication, making it suitable for manufacturing, process control, and material handling systems where legacy PLC-5 architecture is specified.
Key Features
- 16K Word SRAM Memory — Battery-backed volatile memory with EEPROM backup option (1785-ME16, ME32, ME64)
- EtherNet/IP Communication Port — Native Ethernet connectivity for real-time data exchange and remote access
- Multi-Protocol Support — One DH+ port (fixed), one DH+/Remote I/O adapter or scanner port, and one configurable serial port (RS-232/423/422A)
- Up to 512 I/O — Supports 512 mixed I/O or 512 input + 512 output (complementary) configuration
- 13 Chassis Support — Accommodates 1 local chassis plus up to 12 Remote I/O chassis via Universal Remote I/O link
- Series E Enhancement — Enhanced reliability and feature set for demanding industrial environments
Technical Specifications
- User Memory: 16K words (battery-backed static RAM)
- Maximum I/O: 512 (any mix) or 512 input + 512 output (complementary)
- I/O Image Bits: 13 local I/O input, 0 output, 12 remote I/O input, 1 output
- Backplane Current: 3.6 A at 5 Volts
- Serial Communication: RS-232, RS-423, RS-422A configurable
- Chassis Capacity: 1 local + 12 Remote I/O chassis (13 maximum)
- Communication Ports: 1 Ethernet, 1 DH+ (fixed), 1 DH+/Remote I/O (adapter/scanner), 1 serial port
- Program Backup: EEPROM option via 1785-ME modules
- Chassis Mounting: 1771 I/O chassis controller slot
Typical Applications
The 1785-L20E processor is widely deployed in:
- Manufacturing and assembly automation systems requiring EtherNet/IP integration
- Process control applications with distributed I/O over Remote I/O networks
- Material handling and conveyor systems with legacy PLC-5 control logic
- Facility maintenance and retrofit projects where PLC-5 compatibility is required
- Mixed-protocol environments combining DH+, Ethernet, and serial I/O
Compatibility & Replacements
The 1785-L20E Series E is part of the Allen-Bradley PLC-5 Ethernet processor family. For upgrades or similar options, consider the 1785-L40E (PLC-5/40E with 48K memory) or 1785-L80E (PLC-5/80E with 100K memory) for expanded memory requirements. The Series E designation indicates enhanced firmware and reliability features. When sourcing used or refurbished units, verify firmware revision against your application requirements, as program and firmware installation responsibility lies with the end user. Compatible I/O chassis include 1771 series and 1791 I/O blocks via Universal Remote I/O adapters.
