The Allen-Bradley 1785-L40B, also cataloged as the 1785-L40B PLC Processor Module, operates as a dedicated hardware component for executing ladder logic processing and I/O control tasks within PLC-5 control system platforms.

Model Identification

The 1785-L40B is a PLC-5/40 processor module designed for PLC-5 chassis installation. It provides processor execution, SRAM memory storage, DH+ communication, Remote I/O communication, and EEPROM program backup capability.

Hardware Specifications

PLC-5 Processor Architecture

The Allen-Bradley 1785-L40B integrates processor execution functions with PLC-5 backplane communication. The module exchanges data with installed I/O modules through the chassis backplane and manages control instructions stored in processor memory.

The PLC-5 platform uses dedicated communication channels for Data Highway Plus (DH+) and Remote I/O networks. The processor supports distributed I/O control through configured communication links and maintains application logic through SRAM-based memory with EEPROM backup capability.

Ordering Information

• 1 x Allen-Bradley 1785-L40B PLC-5/40 Processor Module
• Compatible PLC-5 chassis installation hardware is not included unless specified separately
• EEPROM backup module is not included unless supplied as an additional component
• Programming accessories and communication cables are ordered separately

Installation Guidelines

Chassis Installation

• Install the module into a compatible PLC-5 chassis slot.
• Verify chassis power is removed before module insertion or removal.
• Ensure the module edge connector is fully seated with the backplane connector.

Communication Wiring

• Use approved DH+ network cabling and termination methods.
• Separate communication cables from high-voltage power wiring to reduce electrical interference.
• Verify network node addressing before system commissioning.

Memory Handling

• Confirm processor memory status before replacing or transferring application programs.
• Use EEPROM backup procedures according to PLC-5 programming requirements.
• Avoid removing memory components during powered operation.

Frequently Asked Questions

• What is the main function of the 1785-L40B?

The 1785-L40B is a PLC-5/40 processor module that executes control programs and manages communication between the processor, chassis backplane, and connected I/O systems.

• What memory type does the 1785-L40B use?

The module uses 48K word SRAM for processor application storage and supports EEPROM for program backup operations.

• Does the 1785-L40B support DH+ communication?

Yes. The module provides DH+ communication capability through dedicated communication channels for PLC-5 network applications.

• Can the 1785-L40B control Remote I/O devices?

Yes. The processor supports Remote I/O communication channels for distributed Allen-Bradley I/O configurations.

• Is the 1785-L40B compatible with ControlLogix chassis?

No. The 1785-L40B belongs to the PLC-5 platform and requires compatible PLC-5 chassis hardware.

• What type of installation does the processor require?

The module requires installation in a compatible PLC-5 chassis with an available processor slot and proper backplane connection.

• Does the processor include non-volatile program storage?

The processor uses SRAM for operating memory and supports EEPROM backup functions for retaining application programs.

• Can the 1785-L40B be removed while powered?

Module removal should follow PLC-5 maintenance procedures. Power isolation is recommended before physical removal or replacement.