1756-L64 Processor Replacement Guide

Overview

The Allen-Bradley 1756-L64 is a ControlLogix 5560 series processor featuring 16 megabytes (MB) of user memory. Originally engineered for large-scale, high-point-count industrial control processes, the 1756-L64 was the flagship controller of the L6 generation. It was designed to run complex sequence execution, motion control profiles, and heavy data coordination tasks across complex factory networks.

Today, the 1756-L64 is discontinued and designated as obsolete by Rockwell Automation. Facilities running this controller face operational risks due to hardware aging, lack of active support, firmware limits (capped at version 20), and the physical degradation of onboard backup batteries.

This guide serves as a master reference for controls engineers, maintenance managers, and system integrators tasked with sourcing direct-replacement legacy hardware or modernizing to newer ControlLogix platforms (such as the 5570 or 5580 families).

---

Legacy Product Information

The 1756-L64 CPU is built upon the ControlLogix 5560 architecture. Its defining technical limitation is that it possesses no integrated Ethernet/IP or USB interfaces. Point-to-point system commissioning and local programming require a specialized RS-232 DF1/DH-485 serial connection (9-pin D-shell).

Technical Specifications

• User Memory: 16 Megabytes (MB)
• I/O Memory: 478 Kilobytes (KB)
• Backplane Current Draw (5.1V DC): 1.2 Amps
• Backplane Current Draw (24V DC): 14 Milliamps (mA)
• Power Dissipation: 3.5 Watts
• Thermal Dissipation: 11.9 BTU/hr
• Integrated Communication Port: One RS-232 Serial Port (Channel 0)
• Onboard Non-Volatile Memory Slot: CompactFlash Card Slot (compatible with 1784-CF128 or 1784-CF64)
• Battery Requirements: 1756-BA2 Lithium Battery Assembly
• Maximum Firmware Support: RSLogix 5000 Version 20.019 (Cannot run Studio 5000 Logix Designer)

Lifecycle Status

The 1756-L64 is classified as End of Life (EOL) / Discontinued. Spare parts and components are no longer manufactured by the OEM. Standard repair services from the manufacturer are severely restricted or discontinued entirely. Critical automation systems requiring a 16MB memory profile must either rely on high-quality surplus inventory or execute a migration to a supported ControlLogix chassis module.

---

Recommended Replacements

When replacing a 1756-L64, you have three primary engineering options depending on your plant’s risk tolerance, budget, and engineering bandwidth.

---

Compatibility Considerations

Before migrating from a legacy 1756-L64 to a newer CPU, evaluate these hardware and software compatibility factors:

1. Serial Communications vs. USB

The 1756-L64 features a physical RS-232 DB9 serial port, often wired to legacy HMIs (like PanelView Standard), bar code readers, weighing scales, or legacy networks (DF1/DH-485). The 1756-L74 and 1756-L84E controllers do not have a serial port; they have a USB port intended solely for programming. If your 1756-L64 uses the RS-232 port for active machine communication, you must integrate a communication module, such as a ProSoft Technology ILX56-PME or an Allen-Bradley 1756-M02AE module, to handle the serial protocols over your EtherNet/IP architecture.

2. Software & Firmware Licensing

The 1756-L64 was programmed with RSLogix 5000 (ending at version 20). If you upgrade to a 1756-L74 or 1756-L84E, you must upgrade your software package to Studio 5000 Logix Designer. Ensure your software license supports these newer targets (typically requiring Version 21 through Version 36).

3. Energy Storage Modules vs. Batteries

The 1756-L64 relies on a 1756-BA2 lithium battery to maintain volatile memory when the chassis is powered down. In contrast, the 1756-L74 utilizes a capacitor-based Energy Storage Module (1756-ESMCAP or 1756-ESMNSE) that charges while the chassis is powered and writes memory contents to the onboard SD card upon power down. The 1756-L84E has an integrated capacitor. Transitioning to capacitors completely eliminates routine maintenance schedules for battery replacements.

4. Backplane & Power Support

Both 1756-L7 and 1756-L8 series processors can fit into existing 1756-A4, -A7, -A10, -A13, and -A16 chassis (Series B, C, or D). However, check your existing power supply (e.g., 1756-PA72 or 1756-PB72) capacity. Ensure the combined draw of all cards, especially if adding new industrial Ethernet cards like the 1756-EN2TR, does not exceed backplane power thresholds.

---

Upgrade Benefits

Upgrading from a 1756-L64 to a modern CPU (such as the 1756-L84E) delivers several operational advantages:

• Elimination of Critical Point of Failure: Scrap the lithium battery (1756-BA2). Modern capacitor-based systems wipe out the risk of memory loss due to unmonitored battery depletion during a scheduled plant shutdown.
• Radical Performance Increase: ControlLogix 5580 processors (L8 series) operate up to 20 times faster than L6 series CPUs. Task execution times drop dramatically, eliminating scan-time jitter.
• Built-In Gig-E Networking: Transitioning to a 1756-L84E provides a dedicated 1-Gigabit onboard Ethernet port capable of managing up to 250 EtherNet/IP nodes natively. This frees up slot space in your rack by eliminating legacy 1756-ENBT or 1756-EN2T communication modules.
• Modern Security Features: Newer firmware environments support controller-based electronic signatures, digital unit protection keylocks, and advanced user access control profiles (via FactoryTalk Security), protecting your plant floor from unauthorized modifications.

---

Common Migration Challenges

• Execution Code Speed Discrepancies: Because the 1756-L84E compiles code directly to its ASIC microengine, execution cycles run significantly faster. If your existing legacy logic depends on slow scan times for timer loops or software-driven debounce signals, this speed jump can cause sequencing errors. Adjust execution structures to use periodic tasks instead of continuous tasks where timing metrics are highly sensitive.
• Deprecated Instructions: Some older instructions used in v20 and lower firmware (such as legacy motion commands or old system calls) are deprecated in newer versions of Studio 5000. Verify configuration integrity prior to code conversion.
• Non-Volatile Memory Incompatibilities: You cannot salvage the old 1784-CF128 CompactFlash card from the 1756-L64. If your system depends on a non-volatile card restore sequence, you must purchase a 1784-SD1 (1 GB) or 1784-SD2 (2 GB) Secure Digital card to accompany your new L7 or L8 series migration controller.

---

Step-by-Step Replacement Procedure

Follow this technical procedure to complete a hardware replacement of a 1756-L64 controller.

Phase 1: Pre-Migration Backup & Safety

1. Isolate Power sources: Ensure the machinery controlled by the rack is in a safe, static state.
2. Retrieve Current Project: Connect to the 1756-L64 via the RS-232 port or your existing network communication card (e.g., 1756-EN2T).
3. Go Online & Upload: Go online with RSLogix 5000. Perform a full upload of the program. Save the file with a clear filename suffix indicating it is the "As-Found" archive.
4. Save Tag Values: Capture the current online tag data values (tag database values) as backup files so you do not lose machine calibration parameters or recipe structures.
5. Verify the Key Switch: Verify that the key switch on the physical front faceplate is set to REM (Remote) or PROG (Program).

Phase 2: Hardware Removal

1. Lock Out Tag Out (LOTO): De-energize the entire local ControlLogix chassis. Verify with a digital multimeter that no hazardous voltages reside on neighboring I/O cards within the chassis.
2. Electrostatic Discharge (ESD) Protection: Put on an ESD-grounding wrist strap. Connect the terminal end to a suitable clean earth ground point on the electrical enclosure.
3. Eject Communications/Auxiliary Connections: unplug any RS-232 DB9 connectors plugged into the front faceplate of the 1756-L64.
4. Remove the Module: Press the plastic retention tabs at the top and bottom of the 1756-L64 module. Slide the module out of the chassis slot tracking guides.
5. (Optional direct-swap prep): If inserting a direct refurbished 1756-L64, extract the existing battery key and slide out the 1756-BA2 battery if you plan to upgrade or keep it as backup. Exchange the CompactFlash card from the bottom compartment and insert it into the new L64 swap unit.

Phase 3: Hardware Installation & Target Swap

For a Direct Swap (Refurbished/Surplus 1756-L64):

1. Ensure the new battery is connected within the internal slide compartment on the replacement L64.
2. Set the front key switch to PROG.
3. Align the module with the card guides in the designated slot and firmly push the card into the chassis backplane until the retention tabs lock shut.
4. Restore power to the chassis.
5. Flash the firmware using ControlFLASH or ControlFLASH Plus to match your target project (e.g., v19.x or v20.x).
6. Connect to the processor and download your uploaded project file. Run online tests.

For a Migration (To 1756-L74 or 1756-L84E):

1. Check that the Energy Storage Module (such as 1756-ESMCAP) is firmly installed (for L7 series units).
2. Insert your new industrial SD card (1784-SD1 or -SD2) into the card slot on the modern processor.
3. Align and slide the new 1756-L74 or -L84E into the chassis. Lock the tabs.
4. Convert your RSLogix 5000 program file to Studio 5000. Change the controller card properties inside your target software from 1756-L64 to 1756-L74 or 1756-L84E. Check for task formatting errors.
5. Restore chassis power.
6. Connect your programming laptop to the Type-B USB port on the front faceplate of the new CPU.
7. Open ControlFLASH and download the latest, stable firmware revision compatible with your software project (e.g., v32.011, v33.x).
8. Once complete, download the converted program via Studio 5000. Set the controller key switch to RUN and monitor execution states carefully.

---

Frequently Asked Questions

Q1: Can I replace my 1756-L64 with a lower memory model like a 1756-L63?

Only if your project's active memory usage is below 8 MB. The 1756-L63 contains 8 MB of user memory compared to the 16 MB onboard the 1756-L64. Check the "Controller Properties" dialog box in your RSLogix 5000 file to analyze exact code and data memory allocation before attempting a hardware downgrade.

Q2: What is the maximum firmware version I can run on a replacement 1756-L64?

The absolute ceiling firmware version for the entire L6 series (ControlLogix 5560) is Version 20.019. It cannot run any Studio 5000 Logix Designer versions (v21 and above).

Q3: My 1756-L64 project uses serial DF1 radio communications. How can I migrate to a 1756-L74 or L84E?

Because modern processors lack native RS-232 connections, you will need a serial interface converter. The industry-standard approach is to add a ProSoft ILX56-PME module in your ControlLogix chassis, or locate a 1756-M02AE module. These devices interface directly with the ControlLogix backplane and map older serial data protocols straight to standard Ethernet or controller tags.

Q4: How long does the 1756-BA2 battery last on a 1756-L64 system?

Typically, a fresh 1756-BA2 battery will maintain your volatile processor memory for approximately 1 to 2 years under unpowered chassis conditions. However, it is highly recommended to replace these batteries annually during scheduled plant shutdowns to prevent sudden program loss.

---

Related Products & Families

When performing hardware upkeep or a controller upgrade in a ControlLogix rack, you may also require compatible modules and support accessories:

• ControlLogix Processors: Allen-Bradley 1756-L61, 1756-L62, 1756-L63, 1756-L71, 1756-L72, 1756-L73, 1756-L81E, 1756-L82E, 1756-L83E.
• Communication Modules: 1756-ENBT (legacy EtherNet/IP), 1756-EN2T, 1756-EN2TR, 1756-EN3TR, 1756-CNB, 1756-CN2R, 1756-DHRIO.
• Energy Storage & Batteries: 1756-BA2 Lithium Battery, 1756-ESMCAP, 1756-ESMNSE (non-storage energy module).
• Power Supplies: 1756-PA72 (85-265V AC), 1756-PB72 (18-32V DC), 1756-PA75, 1756-PB75.
• Memory Storage Devices: 1784-CF128, 1784-SD1, 1784-SD2.

---

Need Help?

Executing a controller swap or upgrading automated systems requires reliable hardware. Whether you need a direct, drop-in refurbished/surplus 1756-L64 to restore a down machine quickly, or a newer 1756-L74 / 1756-L84E package for migration, Palm Parts Solution can assist.

We supply high-quality, fully tested new, surplus, and refurbished ControlLogix parts backed by comprehensive warranties. Contact our technical support and parts team today to source your exact replacement processor and keep your production lines running smoothly.