Allen-Bradley 1785-L46B PLC-5 Controller – 48K Protected Memory

June 10, 2026 • 3 min read • wayne • Industry News

Product Summary

The Allen-Bradley 1785-L46B is a powerful PLC-5/46 programmable controller. It delivers 48,000 words of battery-backed user memory. This module supports up to 2048 I/O points in any mix. Its protected memory safeguards your critical control logic and configurations.

Why Choose the 1785-L46B for Your Control System?

Theme A: Expert Procurement Guide for Engineers

Selecting the correct processor is vital for system reliability. The 1785-L46B meets demanding mid-range automation needs. Its 48-kiloword user memory handles complex sequencing. The controller manages up to 2048 total I/O points. This capacity works for any mix of inputs and outputs. You can even set it for 2048 inputs plus 2048 outputs. This flexibility suits many large-scale installations.

Engineers value the module's robust communication suite. Four ports operate as Data Highway Plus or Remote I/O. Each port can function as an adapter or scanner. This versatility simplifies network design. You also get one serial port for RS-232-C, RS-422-A, and RS-423-A standards. It supports DF1 protocol in full or half duplex. This processor integrates with Bulletin 1771 I/O chassis. It uses 2-slot, 1-slot, or 1/2-slot hardware addressing. This controller supports up to 61 I/O chassis total. Up to 32 of those serve as universal remote racks.

Procurement managers need to know power requirements. This module draws 3.0A from the 5V DC backplane. Its maximum power dissipation is 17.3 Watts. The unit fits in left-most slots of 1771-A series chassis. You can back up the program using EEPROM modules. Compatible modules include the 1785-ME32 and 1785-ME64. The memory protection feature prevents unauthorized access. This secures program blocks and critical operational data.

Theme B: Step-by-Step Installation & User Guide

Proper installation ensures maximum uptime for your production line. Begin by placing the 1785-L46B in the left-most slot. Use a 1771-A1B through 1771-A4B chassis. The module keys to the chassis via specific backplane pins. These are pins 40, 42 and pins 54, 56. This keying prevents incorrect module insertion.

Wiring requires attention to port voltage isolation. The controller provides isolation between communication ports. It also isolates ports from any attached relay cartridge. Testing verifies 500V and 1000V isolation for 60 seconds. This design protects your network from electrical faults. Connect your DH+ or RIO networks to the four front ports. Set each port to operate in adapter or scanner mode. Use the serial port for programming or ASCII communications. This port supports DF1 protocol connection.

After mounting, configure your hardware addressing scheme. You have three options for slot addressing. Use 2-slot, 1-slot, or 1/2-slot modes. The unit scans bit logic at 0.5 ms per K word. A typical program scan runs at 2 ms per K word. I/O scan time varies by network speed. A remote rack scans in 10 ms at 57.6 kbits/s. Faster speeds yield scan times of 7 ms or 3 ms. The controller supports 1771 intelligent modules. It works with 8-point, 16-point, and 32-point I/O modules.