MELSEC Tutorial 12 – Writing to PLC

In this tutorial, we’ll explore how to write programs to a PLC using GX Works3 software. Writing to a MELSEC PLC involves transferring your developed ladder logic or structured programming project into the MELSEC programmable logic controller (PLC) for execution. Understanding this process is crucial for deploying and testing automation logic in real-world scenarios.

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Overview of MELSEC Writing to PLC

The “Write to PLC” operation sends project files, configuration settings, and ladder programs from GX Works3 to the connected PLC. Key steps include establishing communication between your PC and the PLC, verifying project settings, and transferring data securely.

Prerequisites

1. Ensure your PLC is powered on and properly connected to the PC via USB, Ethernet, or another supported interface.
2. Verify that GX Works3 is installed and operational.
3. Confirm that your project is error-free and saved before initiating the write process.

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Step 1: Connecting to the PLC

Establishing Communication

1. Open GX Works3 and load your project.
2. Click the Connection Destination icon in the toolbar or navigate to Online > Connection Destination from the menu.
3. Select the communication method (e.g., USB, Ethernet) and configure the required parameters:
   • For USB: Ensure the device is detected and selected.
   • For Ethernet: Input the PLC’s IP address, port number, and connection parameters.
4. Test the connection by clicking Check Connection to verify communication with the PLC.

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Step 2: Writing the Program to MELSEC PLC

Steps to Transfer

1. Once connected, go to the Online menu and select Write to PLC.
2. In the Write to PLC dialog box:
   • Choose the program components to write, such as Program, Parameters, or Device Memory.
   • Select the Overwrite Write option to replace existing data in the PLC or Partial Write to update only specific sections.
3. Click Execute to start the transfer.

Confirmation and Finalization

During the transfer process, GX Works3 will display a progress bar and status messages. Once the write operation completes:

• Confirm the success message.
• Monitor the PLC for proper operation, ensuring the program runs as expected.

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Step 3: Testing the Program

Monitor and Debug

1. After writing to the PLC, activate the Online Monitor mode in GX Works3 to observe real-time PLC operation.
2. Use the Watch Window to monitor key device statuses and variables.
3. Test your logic by simulating input conditions to verify outputs respond correctly.

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Step 4: Handling Errors During Write Operation

If the “Write to PLC” process encounters errors:

• Connection Issues: Check physical connections and communication settings.
• Project Errors: Resolve syntax errors, mismatched parameters, or memory allocation issues in the project.
• Device Overwrite Warnings: Review write options to ensure no critical data in the PLC is unintentionally overwritten.

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Best Practices for Writing to MELSEC PLC

1. Backup Existing PLC Data: Before writing a new program, back up the PLC’s current configuration and device memory.
2. Validate the Program: Perform a comprehensive project check to ensure all logic is error-free.
3. Minimize Interruptions: Avoid writing to the PLC during active operation to prevent unexpected system downtime.

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Conclusion