Introduction

The Allen-Bradley MicroLogix 1400 is a small and versatile PLC that is used in many small to mid-sized automation systems. It has Ethernet, built-in I/O and is reliable. Like any controller, sometimes you need to clear the memory.

Clearing the memory is needed if a program has become corrupted, if you forgot the password or if the controller is being redeployed for a different project. It can also be part of troubleshooting when other methods don’t solve the issue.

Since clearing the memory will reset the PLC to factory defaults, you should back up any existing program and data before clearing. Once cleared, all user created logic, configuration and stored data will be erased. Having a backup will allow you to get up and running again without having to start from scratch.

Why Clear Memory on a PLC?

There are many reasons you might need to clear the memory of a MicroLogix 1400. One common scenario is to remove an old or corrupted program so you can set up the PLC for a new project. Another is when the controller is password protected but the password is no longer available—clearing memory is the way to get back in. In troubleshooting a reset can also help eliminate faults that persist due to bad logic or misconfigured settings.

Not clearing memory when you should can be risky. Residual programming errors can remain in the system and cause unpredictable machine behavior. A locked controller can prevent maintenance teams from making updates and corrupted instructions can stop the process dead.

Clearing memory gives you a clean slate. You can load a verified program, configure it properly and deploy with confidence. It removes the “unknowns” from the controller so you can focus on the setup rather than the lingering issues.

Factory Reset with Universal Password

Rockwell Automation has a built-in way to clear the memory of the MicroLogix 1400 using a universal password. The password is 65257636 which translates to MLCLRMEM when you type it on a traditional phone keypad. It means “MicroLogix Clear Memory”.

When you are connected to the PLC with Rockwell’s RSLogix 500 or RSLogix Micro software the controller will prompt you for a password before allowing program access. If you don’t know the existing password enter 65257636 and it will clear all memory from the controller.

This will erase everything – the ladder logic, configuration settings and stored data – and return the PLC to its factory default state. Always make sure you have backups before you do a reset. Once cleared the data cannot be recovered.

Step-by-Step Process Using RSLogix

Clearing the memory on a MicroLogix 1400 with RSLogix is a simple process if you go step by step:

1. Connect your PC to the PLC. You can use Ethernet, serial, or USB—whichever connection option is available on your setup.
2. Launch RSLogix 500 or RSLogix Micro. These are Rockwell’s programming tools that let you communicate directly with the controller.
3. Go online with the PLC. This establishes the link between your computer and the MicroLogix 1400 so you can access its configuration.
4. Handle the password prompt. If the controller asks for a password and you don’t know it, enter the universal clear code: 65257636. This immediately wipes the controller’s memory.
5. Watch the status LEDs. The lights on the PLC will update, letting you know that the memory has been cleared and the controller has reset.
6. Load your program. At this point, the PLC is a blank slate. You can download a fresh program from your backup, or leave it in the factory-reset state until it’s ready for redeployment.

This approach is the official Rockwell-recommended method and remains the most dependable way to clear memory on a MicroLogix 1400.

Alternative Methods (Older Units)

Some older MicroLogix units allowed memory to be cleared by powering off the controller, removing the backup battery, and then powering the unit back on. While this method may still work for certain legacy models, it is not typical for the MicroLogix 1400.

The 1400 series uses nonvolatile memory, which means removing power or batteries won’t erase programs or passwords. This makes the universal password method the most dependable and recommended option for modern units.

After Clearing Memory

Once the memory has been cleared, the controller is essentially a blank slate. At this point, you can:

• Reload your program from a backup or create and download a new project.

• Check hardware connections to ensure all I/O modules are detected and functioning.

• Verify communication settings, such as IP addresses or baud rates, to ensure proper connectivity with HMIs, SCADA, or other systems.

• Inspect for persistent issues. If faults continue after memory clearing, the problem may be hardware-related, requiring module replacement or wiring checks.

Practical Tips & Best Practices

• Always backup before clearing. Having the most recent program saved will save valuable time.

• Keep the universal password secure. It’s powerful, but it should only be used by authorized personnel.

• Document program versions. This makes it easier to re-deploy the correct configuration after a reset.

• Use surge protection or UPS. Protecting against power fluctuations reduces the risk of memory corruption.

• Use clearing only when necessary. It’s not a standard troubleshooting step—only reset when other fixes fail or when a clean start is required.

Conclusion

Clearing the memory on a MicroLogix 1400 restores the controller to its factory defaults, wiping all stored programs and data. The universal password method—65257636—is the standard and most reliable way to perform this reset.

While this is an effective solution for corrupted programs, forgotten passwords, or re-deployments, it should always be approached with caution. Every reset means losing existing configurations, so proper backups are critical.

By following best practices and using the reset process wisely, you can minimize downtime, avoid data loss, and keep your automation systems running smoothly.

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