Allen-Bradley 1785-L40B PLC-5 Processor Module

Allen-Bradley 1785-L40B is the PLC-5/40 standard processor module designed for Rockwell Automation’s PLC-5 control systems. It provides 48K words of SRAM for user program and data storage, with battery-backed RAM and EEPROM-based program backup options using 1785-ME16, ME32, ME64, or M100 to retain the control logic during power interruptions. The module supports up to 2048 total I/O (and up to 2048 analog I/O) across its I/O architecture, with four DH+/Remote I/O channels and a configurable serial port that can be set for RS-232-C, RS-422-A, or RS-423-A communications. Backplane current draw is 3.3 A at 5 V, and typical I/O scan times are 10 ms at 57.6 kb/s, 7 ms at 115.2 kb/s, or 3 ms at 230.4 kb/s per rack, with up to 61 I/O chassis in a system. This processor is typically used to execute PLC-5 logic in legacy industrial automation setups that rely on DH+ networks and Remote I/O for field connectivity.