Allen-Bradley 1785-L11B PLC-5/11 Processor 8K Memory

1785-L11B Allen-Bradley PLC-5/11 Standard Controller

Product Introduction

The 1785-L11B from Allen-Bradley is a member of the trusted PLC-5 family, offering a balanced solution for mid-range automation requirements. This standard processor provides sufficient memory and I/O capacity for many common industrial applications, including packaging lines, conveyor systems, and machine control. Its compact design fits neatly into a single 1771 chassis slot. Meanwhile, the built-in Data Highway Plus (DH+) port enables easy integration with other controllers and programming terminals. For users seeking a reliable, no-frills PLC, the 1785-L11B represents an excellent choice.

Memory and Processing Capabilities

The 1785-L11B comes equipped with 8 kilowords of battery-backed static RAM for user program and data storage. This memory capacity handles moderate-sized ladder logic programs effectively. Additionally, the processor supports EEPROM program backup using optional modules such as the 1785-ME16, 1785-ME32, 1785-ME64, or 1785-M100. This feature ensures program recovery even if the battery is depleted.

Unlike its larger siblings, this processor does not include protected memory. Therefore, programs remain accessible for editing unless explicitly safeguarded through other means. For routine maintenance, this openness simplifies program modifications and debugging tasks.

I/O Capacity and System Expansion

The 1785-L11B supports a maximum total I/O count of 512 points in any mix. Alternatively, it accommodates complementary configurations of 384 inputs plus 384 outputs, which uses duplicate addressing for paired modules. Analog I/O capacity also reaches 512 channels, supporting various analog signal types.

Furthermore, this controller manages up to 5 I/O chassis in total. Among these, a maximum of 4 can be universal remote chassis connected via the Remote I/O link. This limitation makes the 1785-L11B ideal for smaller to medium-sized systems where extensive remote expansion is unnecessary. The remaining chassis can be local or extended local configurations.

Communication Ports and Protocols

The front panel hosts a 25-pin D-sub connector labeled as channel 0, which serves as an optically isolated EIA RS-232-C port. This channel supports ASCII and DF1 protocols in full-duplex, half-duplex master, and half-duplex slave modes. Therefore, it connects easily to programming terminals, operator interfaces, or serial printers.

Additionally, an 8-pin mini DIN connector marked channel 1A provides the primary communication interface. This port can be configured in three distinct modes:

• Remote I/O Scanner Mode: Reads and writes I/O data between the controller and remote devices, acting as a supervisory controller.

• Remote I/O Adapter Mode: Allows the controller to monitor its local I/O while communicating with a supervisory controller over the remote link.

• Data Highway Plus (DH+) Mode: Enables peer-to-peer data exchange with other PLC-5 controllers and higher-level system components.

For DH+ networks, maximum cable length depends on the baud rate: 3048 meters at 57.6 kbit/s, 1524 meters at 115.2 kbit/s, and 762 meters at 230.4 kbit/s. Consequently, all devices on the same DH+ link must operate at an identical transmission rate.

Front Panel Indicators and Mode Selection

The 1785-L11B provides several LED indicators for quick status checks:

• BATT (Red): Illuminates when the battery voltage is low, signaling the need for replacement.

• PROC (Green/Red): Green indicates RUN mode, red signals a processor fault.

• FORCE (Amber): Lights up when I/O forces are enabled.

• COMM (Green): Shows communication activity on channel 0.

• Channel 1A Status: Indicates the operational status of the DH+ or Remote I/O link.

A three-position keyswitch on the front panel lets users select the operating mode:

• RUN Mode: The program executes normally, outputs are enabled, and I/O forces work. Data table edits and program saves are allowed.

• PROG Mode: Outputs are disabled. Users can create, modify, or delete ladder, SFC, or data files. Program uploads and downloads with memory modules are possible.

• REM Mode: Enables remote selection of three sub-modes—Remote Program (same as PROG), Remote Test (executes with outputs disabled, no file creation/deletion), and Remote Run (outputs enabled, online editing permitted).

Electrical and Environmental Specifications

The 1785-L11B draws a backplane current of 2.3 amperes at 5V DC, which is relatively low compared to higher-end processors. It dissipates approximately 12 watts of heat during normal operation. The controller operates within a temperature range of 0°C to 60°C (32°F to 140°F) and a non-condensing humidity range of 5% to 95%. Its rugged design withstands industrial vibration and shock, ensuring long-term reliability.

Installation and Compatibility

Installing the 1785-L11B is simple: plug it into any slot of a 1771 I/O chassis. It supports 2-slot, 1-slot, and ½-slot addressing modes, providing flexibility for various I/O module configurations. Moreover, it works seamlessly with all standard 1771-series I/O modules, including 8-point, 16-point, 32-point, and intelligent analog modules. For systems requiring a relay interface, the optional 1785-RC relay cartridge can be added.

Packaging List

Your shipment of the 1785-L11B includes:

• One Allen-Bradley 1785-L11B PLC-5/11 Standard Processor module

• One factory-installed battery for SRAM retention

• Product installation and setup guide (printed)

• Anti-static protective packaging

Note: Programming software, communication cables, and memory modules are sold separately.

Shipping Information

We ship all orders worldwide via FedEx, UPS, or DHL. Standard delivery takes 3 to 7 business days, depending on destination. Express shipping options are also available upon request.

Frequently Asked Questions (FAQ)

1. What is the memory capacity of the 1785-L11B processor?
The 1785-L11B provides 8 kilowords of battery-backed static RAM for user programs and data tables. This capacity suits mid-sized automation projects.

2. How many I/O points can the 1785-L11B handle?
This controller supports up to 512 total I/O points in any mix. In complementary mode, it handles 384 inputs and 384 outputs simultaneously.

3. Does the 1785-L11B support EEPROM program backup?
Yes, it supports EEPROM backup using optional modules like the 1785-ME16, 1785-ME32, 1785-ME64, or 1785-M100 for permanent program storage.

4. What communication protocols are available on the 1785-L11B?
The 1785-L11B includes an RS-232-C port (DF1/ASCII) and a configurable port for Remote I/O or Data Highway Plus (DH+) communication.

5. Can I use the 1785-L11B with existing 1771 I/O modules?
Absolutely. It is fully compatible with all standard 1771-series I/O modules, including digital, analog, and specialty types.