Product Overview

The Allen-Bradley 1785-LT2 functions as a central processing unit within the classic PLC-5 architecture, specifically driving the PLC-5/25 control assembly. This modular processor coordinates mid-range manufacturing lines, complex sequence operations, and analog chemical dosing processes. It provides 13 Kwords of internal battery-backed Static RAM (SRAM) for stable program execution, with expansion capacity up to 21 Kwords using optional cartridge add-ons. Integrated Data Highway Plus (DH+) and universal Remote I/O (RIO) scanners enable the module to manage up to 3072 discrete I/O points and 1024 analog channels across multiple remote chassis clusters. We deliver this computing hardware as a 100% brand new, original factory-sealed unit to ensure mechanical precision and exact firmware timing for legacy system drop-ins.

Technical Specifications

The following data table maps the electrical inputs, processing speeds, and maximum configuration limits of the 1785-LT2 processor:

Engineering Advantages

• Deterministic Distributed Networking: Dedicated onboard DH+ and Universal Remote I/O (RIO) channels maintain highly stable update times for critical devices. At a baud rate of 230.4 kbps, the switch scans an entire 1771 rack subsystem in just 3 milliseconds, minimizing input propagation delays across extensive field wire runs.

• Non-Interrupted Memory Preservation: The internal battery-backed SRAM structure retains essential machine operating profiles and bit registers through major electrical failures. To provide permanent defense against code wipeouts during extended storage, the board accepts plug-in 1785-ME series EEPROM memory cartridges.

• Direct Mechanical Keying Protection: The module features a physical key-switch on the front faceplate. This switch locks the memory execution registers into "Run Mode," preventing unauthorized remote software modifications, accidental network overrides, or unauthorized operator code changes.

• Dual Controller Redundancy Capabilities: The hardware architecture fully supports processor redundancy loops. Linking a secondary tracking unit ensures that control shifts smoothly to the standby processor if a primary CPU hardware fault triggers an interlock, eliminating unplanned facility line halts.

• High-Amp Backplane Drive: The module bus handles 2.5 Amps at 5V DC power directly from the 1771 chassis power supply module. This powerful energy distribution allows the processor to drive local, low-latency intelligent communication modules inside adjacent rack slots.

FAQs

• What critical precaution must maintenance teams observe when replacing the backup battery on the 1785-LT2?

  You must perform the 1770-XYC lithium battery replacement while the control cabinet power remains turned ON. If you extract the old battery while the 1771 chassis is unpowered, the internal volatile SRAM registers lose their electrical bias instantly, deleting your entire automation program and configuration tag database.

• Can the 1785-LT2 operate within any standard 1771 expansion chassis?

  No. The 1785-LT2 processor module must always slide into the designated, left-most master slot of a primary 1771 I/O chassis (such as a 1771-A1B or 1771-A4B). The specialized pins in this specific slot link the processor directly to the backplane communication pathways to enable scanner traffic management.

• How does the hardware handle memory expansion beyond the stock 13 Kwords?

  The faceplate contains a dedicated expansion port that accepts plug-in memory cartridge sub-boards, including the 1785-ME16, 1785-ME32, or 1785-ME64. These accessories expand the total active workspace up to 17 or 21 Kwords to accommodate large math routines or extended recipes.