Product Overview

The Allen‑Bradley 1772‑LS is a processor module belonging to the Mini‑PLC‑2/05 series, part of Rockwell Automation’s legacy PLC‑2 family of programmable logic controllers. As the central processing unit of this control platform, the 1772‑LS (also designated as 1772‑LS/A for Series A) integrates the CPU, system memory, and communication interfaces into a single-slot module that installs directly into a 1771 I/O chassis. Designed as a compact and cost-effective controller for small to mid-sized industrial automation tasks, the Allen‑Bradley 1772‑LS was widely deployed throughout the 1980s and 1990s in applications ranging from machine tool control to conveyor systems and simple process automation.

The 1772‑LS processor features 3K words of CMOS RAM memory, providing robust storage for ladder logic programs and data tables. This memory capacity supports up to 488 timers and counters, with data tables extending to 2944 words, enabling moderate complexity control strategies. The module offers an RS‑232‑C interface via a 15‑pin INTFC socket for programming and communication, supporting connection to the 1770‑T3 programming terminal and other PLC‑2 family peripherals. With its modular design, the Allen‑Bradley 1772‑LS can support up to 16 I/O modules, providing the scalability needed for diverse control system configurations. Although considered obsolete and superseded by modern platforms such as CompactLogix and ControlLogix, the 1772‑LS remains a valuable component for maintaining legacy production lines where full system replacement is not economically viable.

Technical Specifications

Main Features and Advantages

Modular Chassis‑Based Architecture with Scalable I/O
The Allen‑Bradley 1772‑LS is designed as a modular processor that installs directly into a 1771 I/O chassis, offering a scalable architecture where up to 16 I/O modules can be configured to match the specific requirements of each application. This flexibility allows the 1772‑LS to adapt to a wide variety of control tasks, from simple relay replacement to complex sequencing applications. The processor stores all I/O device status data in central read/write memory, enabling efficient data access and deterministic control execution. The 1772‑LS supports block transfer capability, facilitating communication with intelligent I/O modules for applications requiring analog measurement, positioning control, or report generation.

Expanded Math Capabilities and Versatile Programming
Compared to earlier Mini‑PLC‑2 processors, the Allen‑Bradley 1772‑LS features enhanced math functions including addition, subtraction, multiplication, and division, allowing it to handle more sophisticated process calculations beyond simple relay logic. The processor supports online programming, enabling maintenance personnel to make logic modifications while the system remains operational—a critical advantage for facilities requiring continuous production. The 1772‑LS also offers remote mode selection facilities and selectable timer interrupts, providing greater control flexibility for applications requiring precise timing and remote operation.

Data Highway Compatibility and Peripheral Connectivity
The Allen‑Bradley 1772‑LS integrates seamlessly with the broader PLC‑2 family ecosystem through its support for Data Highway communication and compatibility with the 1771‑KA communication interface module. This compatibility enables the 1772‑LS to participate in multi‑processor networks, facilitating coordination between multiple controllers in larger automation systems. The module’s 15‑pin INTFC socket provides a direct connection to the 1770‑RG report generation module, enabling the creation of printed reports from process data, as well as to programming terminals for program development and troubleshooting. The 1772‑LS provides 198‑message storage capacity when used with the report generation module, supporting comprehensive data logging and documentation capabilities.