Allen-Bradley 1785-L60B PLC-5/60 Processor Module for Large Industrial Control Systems

Product Overview

The Allen-Bradley 1785-L60B is a processor module belonging to the PLC-5 family of programmable logic controllers. This PLC-5/60 processor offers 64 kilobytes of user memory, providing capacity for large control programs in applications such as manufacturing lines, material handling systems, and process control. The module is designed for use in the PLC-5 rack-based chassis and supports both local I/O (within the same chassis) and remote I/O via Allen-Bradley's proprietary remote I/O network. The 1785-L60B is a 32-bit processor that executes the PLC-5 instruction set, including ladder logic, sequential function charts, and structured text. It is suitable for controlling medium to large scale automation systems requiring high I/O counts and complex sequencing.

Key Features of Allen-Bradley 1785-L60B

The 1785-L60B processor provides 64K words of user memory, which can be configured for ladder logic, data table storage, and user documentation. The module includes a built-in RS-232 port (DF1 protocol) for programming and connection to operator interfaces, as well as a dedicated remote I/O scanner port for controlling up to three remote I/O racks (expandable with additional scanners). The processor supports the full PLC-5 instruction set, including advanced math, PID loops, block transfers, and communication with intelligent modules. The module features a key switch for selecting Run, Program, and Remote modes, and includes status LEDs for power, run, fault, and battery.

The 1785-L60B is compatible with a wide range of PLC-5 I/O modules, including digital, analog, specialty, and motion control modules. The processor can be programmed using Rockwell Automation's RSLogix 5 software, which runs on Windows-based personal computers. The data table structure is highly flexible, allowing the user to define file types for different data types (e.g., binary, timer, counter, control). The processor includes an onboard real-time clock for time-stamping events and executing time-based tasks. A lithium battery retains the user program and data table in CMOS RAM for extended periods when the processor is powered down. The module also includes a write-protect switch for the user program to prevent unauthorized changes.

Technical Specifications

• Manufacturer: Allen-Bradley (Rockwell Automation)

• Part Number: 1785-L60B

• Series: PLC-5

• Product Type: Programmable Controller Processor (PLC-5/60)

• User Memory: 64 Kwords (approx. 64K bytes)

• Processor Type: 32-bit

• Programming Software: RSLogix 5

• Programming Languages: Ladder logic, SFC, structured text

• Communication Ports: RS-232 (DF1), Remote I/O scanner port

• Remote I/O Support: Yes, up to 3 racks (expandable)

• Local I/O: Chassis backplane

• Real-Time Clock: Yes, battery-backed

• Battery Backup: Lithium battery for memory retention

• Data Table Types: Binary, timer, counter, control, integer, floating point, etc.

• Key Switch Modes: Run, Program, Remote

• Status Indicators: Power, run, fault, battery low, force, etc.

• Power Supply: 5 V DC from chassis backplane

• Operating Temperature: 0 to 60 °C

• Degree of Protection: Open type (NEMA for indoor use)

• Weight: Approx. 1.2 kg (2.7 lb)

Functional Description

The 1785-L60B executes the user's control program by continuously scanning the ladder logic stored in memory. The scan cycle consists of input scan (reading input module data), program scan (executing ladder instructions), output scan (writing output module data), and housekeeping (communication, diagnostics). The processor supports both synchronous and asynchronous I/O updates, providing flexibility for time-critical applications. The remote I/O scanner port communicates with 1771 series I/O chassis located up to several thousand feet away using Allen-Bradley's blue hose cable. The DF1 port can be used for point-to-point communication with a programming terminal, or configured for multi-drop networks using modems or radio links. The processor includes advanced diagnostic capabilities such as event logging, user fault routines, and online editing, allowing program changes while the PLC is running. In the event of a power loss, the battery-backed RAM retains the program and data; when power is restored, the processor can be configured to automatically resume operation in the last mode (Run or Program).

Applications

The Allen-Bradley 1785-L60B is used in large scale industrial automation systems where the PLC-5 platform is already installed. Typical applications include automotive assembly plants, tire and rubber manufacturing, paper mills, water and wastewater treatment facilities, and mining operations. The processor is often found in critical infrastructure applications where long-term reliability and spare parts availability are important. For maintenance and refurbishment, the 1785-L60B provides a drop-in replacement for existing PLC-5/60 processors, extending the life of legacy control systems. System integrators may use this module in retrofit projects where the existing I/O must be preserved but the PLC-5 processor is being upgraded to a higher memory version.