Comprehensive Guide on How to Reset Siemens PLC: Step-by-Step Instructions and Troubleshooting Tips

Key Takeaways

What models are covered?Siemens S7-1200 and S7-1500 PLCs
Methods to reset?Using TIA Portal, Siemens MMC card, and firmware update
Common issues addressed?Memory errors, connection problems, and firmware issues
Expert insights?Advice from certified Siemens specialists and experienced users
Practical examples?Ladder Logic Diagram (LAD) and Master Control Reset (MCR)


At ControlNexus, we understand the critical role that Siemens PLCs play in industrial automation. Established in 2013, we have been a leading provider of Siemens PLCs, HMIs, and Inverters. Knowing how to reset your Siemens PLC can save you time and ensure smooth operations. This guide will provide detailed instructions for resetting Siemens S7-1200 and S7-1500 PLCs, along with troubleshooting tips and practical examples.

Step-by-Step Instructions

Resetting Siemens S7-1200 PLC

Using TIA Portal

  1. Connect to the PLC via TIA Portal:
    • Open TIA Portal and establish a connection with the S7-1200 PLC.
  2. Navigate to Online & Diagnostics:
    • Select your PLC in the project tree and navigate to the Online & Diagnostics tab.
  3. Perform a Factory Reset:
    • In the Online & Diagnostics section, choose the option to reset the PLC to factory defaults.
  4. Power Cycle the PLC:
    • Turn off the PLC for 15 seconds and then turn it back on to complete the reset process.

Using Siemens MMC Card

  1. Insert a Blank MMC Card:
    • Power off the PLC and insert a blank Siemens MMC card.
  2. Power Cycle the PLC:
    • Turn on the PLC and wait until the LEDs stop flashing, indicating the reset is complete.
  3. Remove the MMC Card:
    • Power off the PLC again, remove the MMC card and then power it back on.

Resetting Siemens S7-1500 PLC

Firmware Update

  1. Check and Update the Firmware:
    • Visit the Siemens Industry Support website to download the latest firmware for your S7-1500 PLC.
  2. Install the Firmware:
    • Follow the steps provided in TIA Portal V14 to update the firmware.
  3. Power Cycle the PLC:
    • Restart the PLC to apply the firmware update.

Wiping the CF Card Offline

  1. Put the CPU in Stop Mode:
    • Turn off the PLC and remove the SD card.
  2. Reset to Factory Defaults:
    • Navigate to Settings > Reset > Factory Defaults on the PLC display and perform the reset without the SD card.
  3. Clean the SD Card:
    • Insert the SD card into a computer and delete all files except for essential system files.
  4. Reinsert the SD Card:
    • Turn off the PLC, insert the cleaned SD card, and power it back on.

Common Issues and Troubleshooting

Common Reset Issues

Memory Errors and Solutions

  • Dealing with Internal Memory Errors:
    • If you encounter an internal memory error, try reloading the program multiple times. If the issue persists, contact Siemens support for assistance.
  • Steps to Resolve Download Issues:
    • Ensure the PLC is properly connected and try resetting it through TIA Portal. If problems continue, a hardware replacement may be necessary.

Connection Problems

  • Troubleshooting Connection Issues:
    • Verify network settings and ensure the correct IP address is configured. If the PLC is not reachable, reset the IP address through TIA Portal.
  • Checking Network Settings:
    • Use the diagnostics tools in TIA Portal to check for any network configuration errors and resolve them as needed.

Real-World Problems and Solutions

User Experiences and Solutions

  • Case Study: S7-1200 Reset Issues:
    • One user reported their S7-1200 PLC reset to factory defaults unexpectedly. They resolved this by performing a complete power cycle and reloading the program.
  • Community Solutions:
    • Many users suggest using a blank Siemens MMC card to reset the PLC when it fails to respond to standard reset procedures.

Expert Advice

  • Certified Siemens Specialist Insights:
    • Experts recommend updating the firmware regularly and using diagnostic tools in TIA Portal to monitor the PLC’s health. Regular maintenance can prevent many common issues.

Technical Examples

Ladder Logic Diagram (LAD)

Example Program for Reset Instructions

  • Creating a Simple LAD Program:
    • Develop a basic Ladder Logic program to reset outputs when specific conditions are met.
  • Uploading and Executing the Program in TIA Portal:
    • Use TIA Portal to upload the program to your PLC and test its functionality.

Practical Applications

  • Using LAD for Real-World Reset Scenarios:
    • Implement LAD instructions in real-world scenarios, such as resetting an automated production line after a fault.

Master Control Reset (MCR) Instructions

Introduction to MCR

  • Explanation of MCR Functionality:
    • MCR instructions allow you to control segments of your program, enabling or disabling outputs based on input conditions.

Detailed Programming Example

  • Step-by-Step Guide to Implementing MCR in a PLC Program:
    • Create an MCR zone to manage outputs in an automatic bottle filling system, ensuring safe and efficient operation.

Technical Examples

Master Control Reset (MCR) Instructions

Introduction to MCR

Master Control Reset (MCR) instructions are pivotal in PLC programming, providing the ability to control specific segments of a program. MCR zones enable or inhibit outputs based on input conditions, making them essential for safety and process control applications.

  • MCR Functionality:
    • When the MCR condition is true, the PLC executes the rungs within the MCR zone as if the zone did not exist.
    • When the MCR condition is false, all non-retentive outputs within the MCR zone are reset, regardless of individual rung conditions.

Detailed Programming Example

To illustrate the use of MCR instructions, let’s consider an automatic bottle filling system.

  1. Program Description:
    • The system starts and stops with push buttons.
    • Bottles are filled sequentially, with the conveyor moving bottles under a filling nozzle.
    • The MCR zone is activated to control the filling process, ensuring safety in case of an emergency.
  2. Step-by-Step Guide:
    • Rung 0000: Latching rung to operate the system using Master Start and Stop push buttons.
    • Rung 0001: Introduce the MCR zone with an emergency switch as the input condition.
    • Rung 0002: Use a memory bit to turn on the conveyor motor.
    • Rung 0003: Stop the conveyor motor when the proximity sensor activates, indicating a bottle is in position.
    • Rung 0004: Open the solenoid valve for 5 seconds to fill the bottle.
    • Rung 0005: Restart the conveyor motor after filling is complete.
    • Rung 0006: Count the number of filled bottles and reset the counter after three bottles.

The MCR zone ensures that if the emergency switch is triggered, all outputs are disabled immediately, halting the filling process safely.

Real-World Applications

Implementing MCR instructions in PLC programming enhances safety and control, making them indispensable in industrial automation. By understanding and utilizing these instructions, engineers can design robust and reliable systems.


Resetting Siemens PLCs and understanding advanced programming concepts like Master Control Reset (MCR) are crucial for maintaining efficient and safe industrial operations. With the detailed instructions and troubleshooting tips provided in this guide, you can confidently handle PLC resets and enhance your system’s reliability.

For more advanced guidance and resources, explore the Siemens PLC section on our website. Our expertise at ControlNexus ensures you have access to the best Siemens PLCs, HMIs, and Inverters for your automation needs.

Additional Resources

By following this guide, you will be well-equipped to handle Siemens PLC resets and troubleshooting, ensuring your industrial operations run smoothly and efficiently.

Key Points and Takeaways

  • Siemens S7-1200 and S7-1500 PLCs: Detailed reset instructions using TIA Portal and MMC cards.
  • Common Issues: Solutions for memory errors and connection problems.
  • Expert Advice: Insights from certified Siemens specialists and experienced users.
  • Technical Examples: Practical applications of Ladder Logic and MCR instructions.

Explore our blog for more articles on Siemens PLC programming and automation solutions, and visit our contact page for personalized support.

By integrating these comprehensive instructions and expert advice into your maintenance routine, you can ensure optimal performance and longevity for your Siemens PLCs. Trust ControlNexus to provide the highest quality products and support for your automation needs.


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