Product Description
Product Overview
The Allen-Bradley 1785-L20B is a PLC-5/20 Programmable Logic Controller (PLC) designed for industrial automation applications requiring robust control and communication capabilities. Manufactured by Allen-Bradley, a brand under Rockwell Automation renowned for its industrial control solutions, this module belongs to the legacy PLC-5 series. It features a 16K-word SRAM user memory and supports up to 512 I/O points (any mix) or 512 inputs and 512 outputs in complementary mode, making it suitable for medium-scale control tasks in industries such as manufacturing, process control, and material handling. The 1785-L20B includes multiple embedded communication ports—Data Highway Plus (DH+), a configurable DH+/Remote I/O port, and a serial port—enabling peer-to-peer networking, remote I/O management, and programming workstation interaction. As a discontinued product, it remains critical for maintaining existing PLC-5 systems, with optional EEPROM memory backup available.
Technical Information
| Item | Specifications |
|---|---|
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Series | PLC-5 |
| Model/Part Number | 1785-L20B |
| Description | PLC-5/20 Programmable Logic Controller |
| User Memory | 16K words SRAM |
| Total I/O Capacity | 512 (any mix) or 512 in + 512 out (complementary) |
| Communication Ports | 1 DH+ (fixed), 1 DH+/Remote I/O (configurable), 1 serial (RS-232/423/422A) |
| Backplane Current | 2.3 A at 5 VDC |
| Memory Backup | Lithium battery (1770-XYC); Optional EEPROM (e.g., 1785-ME16) |
| I/O Chassis | 13 total (12 remote max, rack addresses 0-3) |
| Operating Temperature | 0 °C to +60 °C (32 °F to +140 °F) |
| Dimensions | 279 mm H x 51 mm W x 178 mm D (11.0 in x 2.0 in x 7.0 in) |
| Weight | 1 kg (2.2 lb) |