Allen-Bradley 1772-LS Mini PLC-2/05 Processor Module — 3K CMOS RAM, 488 Timers, Up to 16 I/O Modules

Product Overview

The Allen-Bradley 1772-LS​ is a Mini PLC-2/05 processor module manufactured by Rockwell Automation under the Allen-Bradley brand, originally designed as the central processing unit for the classic Allen-Bradley Mini PLC-2 programmable controller system. The Allen-Bradley 1772-LS​ houses 3K words of CMOS RAM backed by an internal lithium battery for program retention during power loss, and it supports a data table capacity of up to 2,944 words, 488 timers/counters, and control of up to 16 local I/O modules (maximum 128 I/O points) mounted in a compatible 1771-series I/O chassis. This processor executes the Mini-PLC-2/05 instruction set, which includes Boolean logic, timers, counters, drum sequencers, and expanded mathematical functions such as add, subtract, multiply, divide, square root, and BCD/binary conversions.Physically, the Allen-Bradley 1772-LS​ occupies a single slot in a 1771 I/O chassis (typically Slot 0) and draws its operating power from the chassis-mounted 1771-Px power supply. The front panel provides a three-position RUN/PROGRAM/REMOTE selector switch, a MEMORY STORE switch for copying the user program to an optional 1772-MJ EEPROM memory cartridge, and two status LEDs—PROC RUN/FAULT and P/S ACTIVE—for at-a-glance diagnostics. A 15-pin D-sub INTFC (interface) socket on the faceplate allows connection to an Allen-Bradley industrial programming terminal (such as the 1770-T3 or 1770-T4), a 1770-RG report generation module, or a 1771-KA Data Highway communication interface module for remote monitoring and uploading/downloading of the control program.The Allen-Bradley 1772-LS​ is a non-redundant, single-processor variant of the Mini PLC-2/05 family (distinct from the 1772-LSP which incorporates an integral power supply section). It is widely retained in legacy process and discrete manufacturing installations where continued operation of proven control logic is preferred over full system migration. With its Data Highway compatibility, online programming capability, and block transfer functions, the Allen-Bradley 1772-LS​ remains a critical spare part for maintaining vintage Allen-Bradley automation systems in industries that still operate Mini PLC-2 based machinery and process lines.

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Description

 

Technical Specifications

Product Model | 1772-LSManufacturer | Rockwell Automation / Allen-BradleyProduct Type | Mini PLC-2/05 Processor Module (CPU, no integral power supply)Program Memory | 3K words CMOS RAM (battery-backed)Data Table Capacity | Up to 2,944 words (configurable 48–2,944 words)Timer/Counter Capacity | 488 timers or counters (combined)Maximum I/O Modules Supported | 16 (local I/O in one 1771 chassis)Maximum I/O Points | 128 discrete I/O pointsInstruction Set | Mini-PLC-2/05 (includes expanded math: +, −, ×, ÷, √, BCD↔Binary)Scan Time (Typical) | Approx. 29 µs (AC I/O update), 30 µs (DC I/O update) per instruction stepBackplane Power Drawn From | 1771 chassis power supply (5 V DC backplane bus)Battery Backup | Internal 3 V lithium cell (user-replaceable) for CMOS RAM retentionInterface Port | 15-pin D-sub (INTFC) for programming terminal / DH module / report generatorEEPROM Option | Accepts 1772-MJ 3K-word EEPROM memory module for non-volatile program storageOperating Temperature | 0 °C to +60 °C (32 °F to 140 °F)Storage Temperature | -40 °C to +85 °CRelative Humidity | 5 %–95 % non-condensingDimensions (H×W×D) | Approx. 114 × 279 × 152 mm (4.5 × 11.0 × 6.0 in. module portion)Mounting | Plugs into 1771 I/O chassis backplane (Slot 0 recommended)Certifications | UL listed, CSA certified, CE marked (per original declaration)

Main Features and Advantages

Data Highway and Terminal Connectivity:The Allen-Bradley 1772-LS​ features a 15-pin INTFC connector that interfaces directly with Allen-Bradley programming terminals (1770-T3/T4), the 1770-RG report generation module for printed process reports, or the 1771-KA Data Highway (DH) interface adapter for networking into a DH/DH+ supervisory system. This allows remote mode selection, online program edits, and real-time monitoring without removing the processor from the rack—a significant advantage for legacy systems still integrated into broader plant networks.Battery-Backed CMOS RAM with EEPROM Archive:User programs and data tables reside in 3K words of CMOS RAM continuously refreshed by an on-board lithium battery. The front-panel MEMORY STORE switch enables one-touch duplication of the running program into an optional 1772-MJ​ EEPROM cartridge plugged into the module, providing a non-volatile archive that can be used to reload the processor after battery failure or RAM corruption. This simple archival method was a hallmark feature of the Mini PLC-2/05 architecture and remains essential for plants maintaining these systems.Expanded Mathematical and Block Transfer Capability:Unlike earlier Mini PLC-2 processors, the Allen-Bradley 1772-LS​ supports extended arithmetic (including square root and BCD conversion) and block transfer instructions, permitting more sophisticated data manipulation and the ability to move blocks of words between the processor and intelligent I/O or communication modules. This makes the Allen-Bradley 1772-LS​ suitable for applications requiring accumulated totals, scaling, or structured data exchange beyond basic relay-replacement logic.Online Programming and Forced I/O:The Allen-Bradley 1772-LS​ permits online program editing and full I/O forcing (both inputs and outputs) when placed in REMOTE PROGRAM mode via the front switch or a connected terminal. Technicians can force individual bits on or off to bypass field devices during commissioning or troubleshooting, then remove forces individually or globally—functionality that dramatically reduces mean time to diagnose wiring or sensor faults on legacy machinery.Diagnostic LEDs and Front-Panel Controls:Two high-visibility LEDs—PROC RUN/FAULT (green/red) and P/S ACTIVE (green)—provide immediate feedback on processor state and chassis power supply status. A red FAULT indication typically signals a watchdog timeout, memory parity error, or fatal run-time condition requiring power cycle or program correction. The three-position RUN / PROGRAM / REMOTE key switch prevents unauthorized mode changes on the plant floor while allowing authorized remote control from a programming terminal.Compact Single-Slot Format with Chassis Compatibility:The Allen-Bradley 1772-LS​ inserts into any standard 1771 I/O chassis and draws its 5 V DC operating current from the chassis backplane, keeping panel wiring to a minimum. It is fully compatible with 1771 series digital, analog, and specialty I/O modules, allowing existing Mini PLC-2 users to leverage a broad ecosystem of readily available legacy spares.

Application Field

The Allen-Bradley 1772-LS​ processor finds its primary application in legacy industrial automation systems that were originally commissioned with Allen-Bradley Mini PLC-2/05 hardware and have remained in continuous service due to proven reliability and the high cost or risk of full control system migration. In discrete manufacturing—such as stamping presses, coil winding machines, bottling lines, and small-batch assembly stations—the Allen-Bradley 1772-LS​ executes ladder-logic sequences that coordinate part presence detection, actuator timing, safety interlocks, and cycle counting. Its 128-point I/O ceiling is well matched to standalone machines where a full-scale PLC-5 or ControlLogix retrofit is not justified.In process auxiliary systems such as water treatment pump stations, boiler burner-management interlocks, and bulk-material blending skids, the Allen-Bradley 1772-LS​ continues to provide dependable sequencing and alarm monitoring. Facilities such as older power plants, paper mills, and food-processing plants often retain the Allen-Bradley 1772-LS​ in secondary or support-control roles (e.g., ash-handling controls, lubrication-oil skid logic, bag-house pulse-jet timing) where the original program has been well-documented and the physical I/O remains serviceable.Because the Allen-Bradley 1772-LS​ supports connection to a Data Highway interface module, it can still exchange data with higher-level SCADA or with a PLC-5 acting as a DH+ bridge, enabling limited integration into modern supervision architectures. For maintenance and reliability engineers tasked with sustaining obsolescent assets, keeping a spare Allen-Bradley 1772-LS​ processor—along with a pre-loaded 1772-MJ EEPROM—is a standard practice to minimize unplanned downtime. The processor is not intended for new designs; it is supplied and stocked exclusively as a replacement/spare part for existing Mini PLC-2 installations.

Related Products

  • 1772-LSP​ — Mini PLC-2/05 processor with integral power supply section; functionally similar CPU to the 1772-LS​ but includes AC/DC power input terminals and paralleling port for chassis power supply.
  • 1772-MJ​ — 3K-word EEPROM memory module that plugs into the 1772-LS​ for non-volatile program backup; essential for disaster recovery of stored logic.
  • 1771-P4R​ / 1771-P6S​ — System power supply modules for the 1771 I/O chassis that provide the 5 V DC backplane power required by the 1772-LS​ processor.
  • 1771-A1B​ / 1771-A2B​ — 8-slot and 16-slot 1771-series I/O chassis into which the 1772-LS​ is installed as the rack CPU.
  • 1770-T3​ / 1770-T4​ — Industrial programming terminals used to create, edit, monitor, and document programs in the 1772-LS​ via the INTFC port.
  • 1770-RG​ — Report generation module that connects to the INTFC port of the 1772-LS​ to print process data, alarm logs, and I/O status reports on demand.
  • 1771-KA​ — Data Highway communication interface module allowing the 1772-LS​ Mini PLC-2/05 system to communicate on an Allen-Bradley DH (Data Highway) network.
  • 1771-IAD​ / 1771-OAD​ — Example 1771-series 24 V DC input and 120 V AC output modules commonly paired in a rack with the 1772-LS​ processor.
  • 1785-L40E​ — PLC-5/40E processor (newer generation); often cited as the migration target when eventually replacing a Mini PLC-2/05 system built around the 1772-LS.
Contact Us WhatsApp / Wechat：+86 18150087953
Phone：+86 18150087953
Email：sales@cxplcmro.com

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