CompactLogix Controller Evolution: Which One Fits Your Automation Needs?

The CompactLogix series from Allen-Bradley has steadily evolved from modest, serial-based controllers to powerful, Ethernet-ready platforms capable of high speed motion control and distributed automation. Whether you're managing a standalone machine or scaling across an entire plant floor, selecting the right generation of CompactLogix controller is key to ensuring long-term reliability, flexibility, and performance.

This guide walks you through the evolution of the CompactLogix family so you can confidently choose the right model for your automation needs.

First Generation: 1769-L20 and L30 (5320 & 5330 Series)

Launched in the early 2000s, these were the entry-level CompactLogix controllers built for small applications. These models lacked Ethernet but served as a transitional bridge from MicroLogix to ControlLogix.

• 1769-L20: 64KB memory, 1x RS-232, max 8 I/O modules

• 1769-L30: 256KB memory, 2x RS-232, max 16 I/O modules

• Protocols: DF1, ASCII, DH-485 (serial only)

• Notes: Required proximity to a power supply (within 4 modules), shared 1769 I/O with MicroLogix 1500

These are ideal for legacy replacements, small test rigs, or basic serial-based applications.

Best for: Legacy or educational systems with minimal I/O and serial communication.

Second Generation: 1769-L31, L32E, L35E (L3x Family)

Introduced in 2003, this generation brought Ethernet capability, CompactFlash storage, and greater I/O scalability.

• 1769-L31: 512KB memory, 16 I/O modules, 1x RS-232

• 1769-L32E: 768KB memory, 30 I/O modules, built-in Ethernet

• 1769-L35E: 1.5MB memory, 30 I/O modules, multitasking support

• Features: Key switch, CompactFlash for non-volatile memory, 4–8 task support

These became a workhorse across industries for reliable distributed control with minimal cost.

Best for: Mid-sized machine automation, Ethernet-based I/O, and general-purpose control.

Special Case: 1769-L23 Series (All-in-One CompactLogix)

Launched around 2008, the L23 series integrated the controller and I/O in one compact housing. It was cost-effective, space-saving, and easy to program but with tradeoffs.

• 1769-L23E-QB1B / L23E-QBFC1B: 512KB battery-backed volatile memory

• Built-in I/O: 16 digital in/out, analog I/O (select models), HSC inputs

• Ethernet support on select models

• Limited expansion (2–3 additional modules)

Great for OEMs, packaging equipment, or HVAC where simplicity and low cost are key.

Best for: Compact machines with fixed I/O needs and low complexity.

Third Generation: 1768-L43 and L45 (L4x Series)

The L4x series brought ControlLogix-style performance to CompactLogix, including motion control via 1768-SERCOS modules and modular network support.

• 1768-L43: 2MB memory, 2x 1768 expansion slots, 16 I/O

• 1768-L45: 3MB memory, 4x 1768 expansion slots, 30 I/O

• Supports motion, redundancy, and advanced diagnostics

• Modules: 1768-ENBT (Ethernet), 1768-EWEB (web), 1768-CNB (ControlNet)

This is the go-to generation for coordinated motion, drives, and multi-network plant systems ideal for high-performance packaging, robotics, and process automation.

Best for: High-speed, motion-centric applications or multi-zone automation systems.

CompactLogix Controller Comparison Table

Final Takeaway: Matching Controller to Application

Choosing the right CompactLogix controller depends on application size, network requirements, I/O scale, and performance needs.

• Go with Gen 1 for basic serial I/O systems or legacy replacements

• Choose Gen 2 for standard Ethernet applications and multitasking

• Pick Gen 2.5 for compact machines needing built-in I/O and minimal expansion

• Select Gen 3 for motion, high-speed performance, and system-wide integration

For more information, contact PLG Automation:
Email: sales@plgautomation.com
Phone: 800-906-9271