Understanding Modbus and Structured Text

Oct 13, 2025 by talynt.org 92 views

Introduction

In this article, we will delve into the world of Panasonic FPWINPro Structured Text and explore how to send counter values to a Modbus holding register using the AFPX-COM5 module. We will assume that you have a basic understanding of PLC programming and Modbus communication.

Understanding Modbus and Structured Text

Modbus is a widely used protocol for communicating with industrial devices, including PLCs. It allows for the exchange of data between devices over a serial communication link. Structured Text, on the other hand, is a programming language used to write programs for PLCs. It is a text-based language that allows for the creation of complex logic and control programs.

Setting Up the AFPX-COM5 Module

To send counter values to a Modbus holding register, you will need to set up the AFPX-COM5 module on your Panasonic FP-X C60R PLC. The AFPX-COM5 module is a Modbus communication module that allows you to communicate with Modbus devices over a serial communication link.

Configuring the Modbus Settings

To configure the Modbus settings on the AFPX-COM5 module, follow these steps:

Open the FPWINPro software and connect to your PLC.
Go to the "Device" menu and select "Configure".
In the "Configure" window, select the "Modbus" tab.
In the "Modbus" tab, select the "Modbus Settings" button.
In the "Modbus Settings" window, configure the following settings:

Modbus ID: Set the Modbus ID to a unique value (e.g. 1).
Baud Rate: Set the baud rate to 9600.
Data Bits: Set the data bits to 8.
Stop Bits: Set the stop bits to 1.
Parity: Set the parity to None.

Click "OK" to save the changes.

Writing the Structured Text Program

Now that we have configured the Modbus settings, we can write the Structured Text program to send the counter value to a Modbus holding register.

Counter Variable

First, we need to declare a counter variable to store the counter value. We can do this using the following code:

VAR
    Counter : INT;
END_VAR

Modbus Function Block

Next, we need to create a Modbus function block to send the counter value to a Modbus holding register. We can do this using the following code:

MODBUS_WRITE(
    Address := 0x01,  // Modbus address
    SlaveID := 1,     // Modbus ID
    Register := 0x0000,  // Register address
    Value := Counter    // Value to write
);

Main Program

Now that we have declared the counter variable and created the Modbus function block, we can write the main program to increment the counter value every second and send it to the Modbus holding register. We can do this using the following code:

PROGRAM
    Counter := Counter + 1;
    MODBUS_WRITE(
        Address := 0x01,  // Modbus address
        SlaveID := 1,     // Modbus ID
        Register := 0x0000,  // Register address
        Value := Counter    // Value to write
    );
END_PROGRAM

Compiling and Downloading the Program

Once we have written the Structured Text program, we can compile and download it to the PLC using the FPWINPro software.

Testing the Program

To test the program, we can use a Modbus master device to read the counter value from the Modbus holding register. We can do this by setting up a Modbus master device and configuring it to read the counter value from the Modbus holding register.

Conclusion

In this article, we have explored how to send counter values to a Modbus holding register using the AFPX-COM5 module and Structured Text programming language. We have walked through the steps to configure the Modbus settings, write the Structured Text program, and compile and download the program to the PLC. We have also tested the program using a Modbus master device.

Troubleshooting Tips

If you encounter any issues while implementing this program, here are some troubleshooting tips to help you resolve the problem:

Check the Modbus settings: Make sure that the Modbus settings are correctly configured on the AFPX-COM5 module.
Check the Structured Text program: Make sure that the Structured Text program is correctly written and compiled.
Check the Modbus master device: Make sure that the Modbus master device is correctly configured to read the counter value from the Modbus holding register.

References

Panasonic FPWINPro User Manual: This manual provides detailed information on how to use the FPWINPro software and configure the AFPX-COM5 module.
Modbus Protocol Specification: This specification provides detailed information on the Modbus protocol and how to implement it.

Appendix

Here is a summary of the Structured Text program:

VAR
    Counter : INT;
END_VAR
PROGRAM
Counter := Counter + 1;
MODBUS_WRITE(
Address := 0x01,  // Modbus address
SlaveID := 1,     // Modbus ID
Register := 0x0000,  // Register address
Value := Counter    // Value to write
);
END_PROGRAM

Introduction

In our previous article, we explored how to send counter values to a Modbus holding register using the AFPX-COM5 module and Structured Text programming language. In this article, we will answer some frequently asked questions (FAQs) related to Panasonic FPWINPro Structured Text for Modbus.

Q: What is the difference between Modbus RTU and Modbus TCP?

A: Modbus RTU (Remote Terminal Unit) and Modbus TCP (Transmission Control Protocol) are two different communication protocols used for Modbus communication. Modbus RTU is a serial communication protocol that uses a serial communication link to communicate with devices, while Modbus TCP is an Ethernet-based protocol that uses TCP/IP to communicate with devices.

Q: How do I configure the AFPX-COM5 module for Modbus communication?

A: To configure the AFPX-COM5 module for Modbus communication, follow these steps:

Open the FPWINPro software and connect to your PLC.
Go to the "Device" menu and select "Configure".
In the "Configure" window, select the "Modbus" tab.
In the "Modbus" tab, select the "Modbus Settings" button.
In the "Modbus Settings" window, configure the following settings:

Modbus ID: Set the Modbus ID to a unique value (e.g. 1).
Baud Rate: Set the baud rate to 9600.
Data Bits: Set the data bits to 8.
Stop Bits: Set the stop bits to 1.
Parity: Set the parity to None.

Click "OK" to save the changes.

Q: How do I write a Structured Text program to send a counter value to a Modbus holding register?

A: To write a Structured Text program to send a counter value to a Modbus holding register, follow these steps:

Declare a counter variable to store the counter value.
Create a Modbus function block to send the counter value to a Modbus holding register.
Write the main program to increment the counter value every second and send it to the Modbus holding register.

Here is an example of a Structured Text program:

VAR
    Counter : INT;
END_VAR
PROGRAM
Counter := Counter + 1;
MODBUS_WRITE(
Address := 0x01,  // Modbus address
SlaveID := 1,     // Modbus ID
Register := 0x0000,  // Register address
Value := Counter    // Value to write
);
END_PROGRAM

Q: How do I troubleshoot issues with my Modbus communication?

A: To troubleshoot issues with your Modbus communication, follow these steps:

Check the Modbus settings on the AFPX-COM5 module.
Check the Structured Text program for errors.
Check the Modbus master device for errors.
Use a Modbus simulator to test the communication.

Q: Can I use the AFPX-COM5 module with other Modbus protocols?

A: Yes, you can use the AFPX-COM5 module with other Modbus protocols, such as Modbus ASCII and Modbus TCP.

Q: How do I update the firmware of the AFPX-COM5 module?

A: To update the firmware of the AFPX-COM5 module, follow these steps:

Download the latest firmware from the Panasonic website.
Connect the AFPX-COM5 module to your PLC.
Open the FPWINPro software and connect to your PLC.
Go to the "Device" menu and select "Firmware Update".
Follow the on-screen instructions to update the firmware.

Conclusion

In this article, we have answered some frequently asked questions (FAQs) related to Panasonic FPWINPro Structured Text for Modbus. We hope that this article has provided you with the information you need to troubleshoot issues with your Modbus communication and to write effective Structured Text programs for Modbus communication.

References

Panasonic FPWINPro User Manual: This manual provides detailed information on how to use the FPWINPro software and configure the AFPX-COM5 module.
Modbus Protocol Specification: This specification provides detailed information on the Modbus protocol and how to implement it.

Appendix

Here is a summary of the FAQs:

Q: What is the difference between Modbus RTU and Modbus TCP?
A: Modbus RTU is a serial communication protocol that uses a serial communication link to communicate with devices, while Modbus TCP is an Ethernet-based protocol that uses TCP/IP to communicate with devices.
Q: How do I configure the AFPX-COM5 module for Modbus communication?
A: To configure the AFPX-COM5 module for Modbus communication, follow the steps outlined in the article.
Q: How do I write a Structured Text program to send a counter value to a Modbus holding register?
A: To write a Structured Text program to send a counter value to a Modbus holding register, follow the steps outlined in the article.
Q: How do I troubleshoot issues with my Modbus communication?
A: To troubleshoot issues with your Modbus communication, follow the steps outlined in the article.
Q: Can I use the AFPX-COM5 module with other Modbus protocols?
A: Yes, you can use the AFPX-COM5 module with other Modbus protocols, such as Modbus ASCII and Modbus TCP.
Q: How do I update the firmware of the AFPX-COM5 module?
A: To update the firmware of the AFPX-COM5 module, follow the steps outlined in the article.