ControlLogix Upgrade Paths: Legacy to Current L7/L8 Series

Overview

The Rockwell Automation Allen-Bradley ControlLogix platform has served as a cornerstone of industrial control systems for over two decades. However, the first-generation ControlLogix 5555 (1756-L55) and second-generation ControlLogix 5560 (1756-L6x) processors have long passed their active lifecycles, moving into End-of-Life (EOL) and discontinued phases. Maintaining these legacy controllers exposes facilities to risks including extended downtime, lack of official manufacturer support, and component scarcity.

Upgrading to the ControlLogix 5570 (1756-L7x) or ControlLogix 5580 (1756-L8x) series ensures system reliability, expands communication processing power, and enables enhanced cybersecurity protocols. This technical guide outlines the precise hardware, software, and network pathways required to migrate from legacy platforms to current L7 and L8 control architectures.

Legacy Product Information

Legacy ControlLogix systems primarily consist of the 1756-L55 series and the 1756-L61, 1756-L62, 1756-L63, 1756-L64, and 1756-L65 controllers. These devices relied on older architectures designed around PCMCIA or CompactFlash non-volatile memory and physical lithium backup batteries to maintain controller state during power outages.

• 1756-L55 (Logix5555): Supported up to RSLogix 5000 v16. These units used external non-volatile memory modules (1756-M12, M13, etc.) and connected via serial RS-232 ports. They utilized 1756-BA1 batteries.
• 1756-L6x (Logix5560): Supported up to RSLogix 5000 v20. They featured a built-in RS-232 serial interface and utilized CompactFlash cards (1784-CF128) for non-volatile storage. They relied on 1756-BA2 energy cells (lithium batteries) which required periodic testing and proactive replacement schedules.

Both platforms are characterized by backplane communication limits, processing cores that handle command execution and system overhead sequentially, and limited native network connectivity, requiring separate communication bridge modules like the 1756-ENBT or 1756-CN2 for network access.

Recommended Replacements

When migrating from legacy ControlLogix processors, engineers have two primary upgrade paths: the 1756-L7 series (Logix5570) or the newer 1756-L8 series (Logix5580).

Migration Matrix

Selecting the 1756-L8x series is generally standard practice for new deployments and comprehensive retrofits. The L8 series features an integrated 1 Gbps EtherNet/IP port, vastly superior backplane performance, and a modern dual-core execution engine that segregates safety/logic processing from communication tasks.

Compatibility Considerations

Upgrading legacy controllers requires reviewing hardware dependencies, network topologies, and programming environment changes.

Physical and Chassis Compatibility

Legacy systems run on 1756-A4, 1756-A7, 1756-A10, 1756-A13, and 1756-A17 chassis. While L7 and L8 controllers fit into existing 1756 slots, the backplane revision matters. L8 controllers require Series B or Series C chassis (and power supplies like the 1756-PA72/PB72 or 1756-PA75/PB75) to utilize their high-speed backplane capabilities. If mounted in older Series A chassis, L8 performance defaults to legacy bus speeds.

Energy Storage Systems

L7 and L8 series controllers do not use lithium batteries. Instead, they use capacitor-based energy storage modules.

• 1756-L7x uses the 1756-ESMCAP (or 1756-ESMNSE for non-volatile storage without energy reserve) to write execution memory to the Secure Digital (SD) card (1784-SD1 or 1784-SD2) upon power failure.
• 1756-L8x integrates an internal capacitor directly on the board, eliminating the need to source external energy maintenance modules.

Communication Protocols

Legacy serial communication (RS-232) is absent from both L7 and L8 controllers. Direct replacement of a serial-dependent program requires adding a module like the ProSoft Technology MVI56E-MCM (for Modbus RTU) or utilizing an EtherNet/IP-to-Serial gateway. If upgrading to the L8 with built-in Ethernet (e.g., 1756-L83E), check your IP structuring. The embedded port operates under its own network interface card, and heavy producer/consumer tags or remote I/O layouts must be correctly mapped to this port or delegated to supplementary communication adapters like the 1756-EN2TR or 1756-EN4TR.

Software and Firmware Migration

Legacy code written in RSLogix 5000 (v10 through v20) must be converted to Studio 5000 Logix Designer.

• To go to L7: Requires Studio 5000 Logix Designer v21 or higher.
• To go to L8: Requires Studio 5000 Logix Designer v28 or higher (v32+ recommended for security features). During code migration, legacy Add-On Instructions (AOIs) and custom firmware profiles must be evaluated for compatibility, especially when migrating obsolete I/O profiles.

Upgrade Benefits

Transitioning to current-generation ControlLogix hardware provides critical functional advances:

• Processing Velocity: The 1756-L8x execution engine offers processing speeds up to 10-times faster than L7 and up to 20-times faster than legacy L6 series, removing scan-time bottlenecks in highly complex process control.
• Elimination of Maintenance Overhead: Capacitor runtimes remove the periodic inspection and PM requirements associated with ordering, replacing, and checking 1756-BA2 and 1756-BA1 batteries.
• Native Diagnostics and Security: L8 series processors feature firmware-signed encryption, role-based access control integration via FactoryTalk Security, and integrated physical mode switches, decreasing vulnerability to unauthorized logical modifications.
• Expanded Memory Capacities: Legacy processors were limited to 8 MB of user memory. Current L8 series controllers offer up to 40 MB of user memory, accommodating large-scale virtualization and data packing configurations.

Common Migration Challenges

• Non-Volatile Memory Transition: Users must transition legacy configurations stored on early PCMCIA cards or CompactFlash cards to 1784-SD1 or 1784-SD2 SD cards. Ensure formatting is FAT32 and the cards are industrial-grade to prevent write-corruption.
• Message Instruction Targets: LEGACY MSG paths targeting remote nodes often point to legacy ENBT cards. When these cards are retired and consolidated onto the L8's onboard module, communication paths (CIP paths) in MSG instructions must be physically re-mapped inside the program logic.
• Deprecated Hardware Profiles: During RSLogix to Studio 5000 file conversion, verify that legacy remote I/O adapters (such as 1756-DHRIO or 1756-RIO) and older drive profiles are compatible with the targeted firmware version. Some legacy 1756 analog and digital modules may require driver emulation or full physical replacement with modern equivalents.

FAQ

Q: Can I put a 1756-L83E controller into a legacy 1756-A10 Series A chassis?

Yes. The L8 series is physically compatible with legacy Series A chassis. However, it will communicate across the backplane at legacy PCI speeds rather than utilizing the enhanced, high-speed Gigabit backplane speed inherent to Series B and Series C chassis.

Q: What is the direct replacement for a 1756-L61 that used a serial connection to dial a modem?

Because L7 and L8 series controllers do not contain serial ports, you must route serial connectivity through a network adapter. Use a 1756-EN2T or 1756-EN4TR module coupled with an industrial EtherNet/IP-to-Serial gateway (such as a ProSoft or HMS Anybus device), or source an in-chassis serial module like the ProSoft MVI56E-GSC.

Q: Do I need to buy a new software license when moving from RSLogix 5000 to Studio 5000?

If your legacy RSLogix 5000 software license is wrapped in an active Software Maintenance Agreement (Support Agreement), you are entitled to download and activate the equivalent tier of Studio 5000 Logix Designer. If your license has lapsed, you must purchase a modern Studio 5000 standard or professional license activation.

Q: Is there a functional difference in memory allocation between L6 and L8 processors?

Yes. Legacy L6 and L7 controllers specify distinct user memory pools for Data and Logic configurations. The L8 series consolidates memory into a single pool, eliminating constraints where logic space is exhausted while data space remains available, allowing for more versatile tag structuring.