Product Overview of the Allen-Bradley 1785-L40B

The Allen-Bradley 1785-L40B belongs to the trusted PLC-5 family. This processor module handles medium to large control applications. You must mount it in a 1771 series chassis. Compatible chassis include the 1771-A1B, A2B, A3B, and A4B models. The controller offers robust memory for complex logic programs. Its design focuses on high reliability in industrial environments.

Technical Specifications

• Brand: Allen-Bradley
• Part Number: 1785-L40B
• Product Type: Programmable Logic Controller (PLC)
• Product Family: PLC-5
• Processor Type: PLC-5/40 Standard
• User Memory: 48 Kilowords (48K)
• Memory Type: Battery-Backed Static RAM
• Maximum Total I/O: 2048 (any mix) or 2048 In + 2048 Out
• Maximum Analog I/O: 2048 channels
• Maximum I/O Chassis Total: 61 units
• Maximum I/O Chassis per Link: 32 units
• Embedded Communication Ports: 4 DH+/Remote I/O, 1 Serial Port
• Serial Port Standards: RS-232, RS-423, RS-422A
• Backplane Current Load: 3.3A
• Power Dissipation: 17.3W
• Recommended Power Supply: 1771-P4S, -P6S, -P4S1, -P6S1
• Operating Temperature: 0 to 60 °C (32 to 140 °F)
• Non-Operating Temperature: -40 to 85 °C (-40 to 185 °F)
• I/O Scan Time per Rack: 10 ms at 57.6 kbit/s, 7 ms at 115.2 kbit/s, 3 ms at 230.4 kbit/s
• Control Coprocessor Port: Yes
• Battery: 1770-XYC (for memory backup)

Memory and I/O Capacity

The Allen-Bradley 1785-L40B provides 48K words of user memory. This memory supports complex ladder logic and data tables. You can configure the I/O in two different ways. The first option supports 2048 mixed I/O points total. The second option supports 2048 inputs and 2048 outputs separately. This flexibility suits large scale automation projects perfectly. The controller manages up to 61 total I/O chassis. One local rack holds the processor itself. The remaining 28 racks operate as remote I/O racks.

Communication and Networking Features

This 1785-L40B controller includes four combined DH+/Remote I/O ports. Each port acts as an adapter or a scanner. You can use these ports on four independent networks. This setup provides excellent network segmentation capabilities. A single serial port supports RS-232, RS-423, and RS-422A. This serial channel works best for point-to-point communication. Short distance connections benefit from this versatile serial interface.

Program Backup and Non-Volatile Storage

The 1785-L40B supports optional EEPROM backup memory. These cards serve as non-volatile memory for your programs. Use the 1785-ME16 for 16K words of storage. Use the 1785-ME32 for 32K words of storage. The 1785-ME64 provides 64K words of storage. The 1785-ME100 offers 100K words of storage. This feature allows fast program recovery without a computer. The battery-backed RAM keeps data safe during short power losses. Replace the 1770-XYC battery periodically to maintain memory retention.

Installation and Environment Requirements

Mount the Allen-Bradley 1785-L40B into a 1771 chassis only. Ensure the backplane can supply 3.3A of current. Use a compatible power supply like the 1771-P4S or P6S series. Keep the operating temperature between 0 and 60 °C. The module survives storage temperatures from -40 to 85 °C. This tolerance makes it suitable for many factory floors. Avoid condensing humidity and conductive dust around the unit.

Package Contents

• One (1) Allen-Bradley 1785-L40B PLC-5/40 Processor Module
• One (1) Product Manual and Installation Guide

Common FAQs for the 1785-L40B

1. What is the maximum I/O count for the 1785-L40B?

The 1785-L40B supports 2048 total I/O in mixed configuration. It also supports 2048 inputs plus 2048 outputs separately. This capacity fits most medium to large industrial systems easily.

2. Does the 1785-L40B require a specific battery for memory backup?

Yes, the 1785-L40B uses the 1770-XYC battery for RAM backup. This battery retains your program during power loss. Replace it annually for best performance and data safety.

3. Can I use EEPROM with the 1785-L40B controller?

Yes, the 1785-L40B accepts several EEPROM options. Use the 1785-ME16, ME32, ME64, or ME100 cards. These cards store your program without a continuous power source.

4. What communication protocols are built into the 1785-L40B?

The 1785-L40B includes four DH+/Remote I/O ports. It also has one serial port for RS-232, RS-423, or RS-422A. This variety supports many legacy and modern network needs.

5. How many remote I/O chassis can the 1785-L40B handle?

The 1785-L40B manages up to 61 total I/O chassis. This total includes one local chassis and 60 remote chassis. Each I/O link supports up to 32 chassis directly.