Product Overview

The Allen-Bradley 1785-L80B is a high-performance central processing unit (CPU) belonging to the PLC-5® Enhanced controller family. Engineered to manage large-scale and complex automation architectures, the 1785-L80B provides extensive memory capacity and advanced communication versatility. It acts as the primary intelligence hub for 1771 Universal I/O systems, capable of governing local chassis operations while simultaneously coordinating distributed I/O over remote networks.

With a memory capacity of 100K words, this controller is designed for high-density applications that require extensive data logging, complex mathematical instructions, and large program storage. The 1785-L80B is particularly valued in legacy system maintenance and modern plant expansions due to its ability to bridge classic Data Highway Plus (DH+) networks with sophisticated remote I/O configurations.

Advanced Communication and Network Architecture

The 1785-L80B stands out for its multi-channel connectivity, offering four built-in ports (Channels 1A, 1B, 2A, and 2B) that can be individually configured based on system requirements.

• Configurable Port Flexibility: Each of the four channels can be assigned as a Remote I/O Scanner, a Remote I/O Adapter, or a DH+ node. This allows the processor to either control a network of remote racks or act as a slave device within a larger hierarchy.

• Peer-to-Peer Networking: Utilizing Data Highway Plus (DH+), the module facilitates seamless messaging between multiple PLC-5 controllers, SLC 500 systems, and HMI interfaces without complex routing hardware.

• Legacy Serial Support: Channel 0 is a dedicated 25-pin RS-232C port supporting DF1 full-duplex, half-duplex, and ASCII protocols, ideal for modem connections, barcode readers, or direct PC programming.

• System Capacity: Supports up to 3072 total I/O (any mix of inputs and outputs) and can manage up to 125 remote I/O racks, ensuring scalability for massive industrial deployments.

Technical Specifications

• Manufacturer: Allen-Bradley (Rockwell Automation)

• Model Number: 1785-L80B

• Controller Series: PLC-5/80 Enhanced

• User Memory: 100,000 Words

• Total I/O Max: 3072 (Any mix)

• Backplane Current Draw: 3.3A @ 5V DC

• Communication Channels: 4 Configurable (DH+ or RIO) plus 1 RS-232C Serial Port

• Programming Software: RSLogix 5

• Operating Temperature: 0 to 60°C (32 to 140°F)

• Weight: 1.32 kg (2.91 lbs)

• Dimensions: 4.8 x 15.2 x 27.3 cm

Diagnostics and System Reliability

The 1785-L80B includes a comprehensive front-panel diagnostic suite to assist maintenance personnel in real-time troubleshooting:

• Status LEDs: Dedicated indicators for PROC (Processor status), FORCE (I/O forcing active), and COMM (Communication activity) provide instant visual feedback on system health.

• Non-Volatile Storage: Supports EEPROM modules for secure program backup, ensuring that the control logic is preserved during long-term power outages.

• Battery Backup: Integrated lithium battery maintains the CMOS RAM to prevent data loss during routine power cycles.

• Hardware Keying: Mechanical keying on the 1771 chassis prevents the accidental insertion of the wrong processor type, protecting the backplane circuitry.