FX3G-485-BD: Compatibility with Modbus Communication

Question:

I am currently managing a project that involves capturing data from a Mitsubishi PLC FX3G using RS485. Through my research, I have discovered that I need to incorporate a communication module. I have two options: FX3G-485-BD and FX3G-CNV-ADP -> FX3U-485ADP-MB. Unfortunately, I do not have enough space in the PLC to accommodate the second option as it needs to be added to the left of the PLC. Therefore, the first choice is the most suitable for me. Can the FX3G-485-BD module support the Modbus communication protocol? Any assistance would be greatly appreciated.

Top Replies

No, it does not automatically generate the CRC, so you will need to create your own. I encountered this situation a few years back when the PLC was equipped with the 232 BD board. Initially, the task of generating the CRC16 for each message seemed daunting, but the process itself is straightforward. Sending and receiving data is also simple - just fill the registers with the necessary values and activate the send bit. However, when receiving data, it is important to verify its validity by running the CRC check and ensuring it matches the received CRC.

Parky stated that the second option does not support the Modbus Protocol because it does not generate the necessary CRC. It would require writing your own code for this purpose. This situation was encountered a few years ago when dealing with a programmable logic controller (PLC) equipped with the 232 BD board. The process involves generating the CRC16 for each message, but after that, sending and receiving data is straightforward. To send data, simply populate the registers with the desired values and set the send bit. Receiving data is also uncomplicated, but it is important to verify the data's validity by running the CRC check and confirming it matches the received CRC. Additionally, the inquiry is made about addressing Modbus from the PLC tags.

The FX3U 485-MB version reportedly includes its own processor that handles numerous functions, such as generating CRC. While I personally have not utilized this feature, a programming manual for the FX3U-485ADP-MB model can be found in a video on Bing. You can access the manual directly at https://dl.mitsubishielectric.com/dl/fa/document/manual/plc_fx/jy997d26201/jy997d26201g.pdf.

Yes, the FX3G-485-BD module does indeed support the Modbus communication protocol. Note that it uses the RS485, 2-wire, half-duplex configuration. Your choice seems to be right in your context, considering the space limitation you mentioned. When you start implementing, remember to adjust the baud rate and other communication parameters correctly to ensure smooth communication.

Yes, the FX3G-485-BD module can indeed support the Modbus communication protocol. Although it's more of a bare-bones option compared to the FX3U-485ADP-MB, it should adequately serve your needs given your PLC space constraints. It supports both Modbus RTU and ASCII formats. Just make sure to properly set up the Modbus settings on your PLC program to ensure seamless communication.

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Frequently Asked Questions (FAQ)

FAQ: 1. Is the FX3G-485-BD module compatible with Modbus communication protocol?

Answer: - Yes, the FX3G-485-BD module supports Modbus communication protocol for capturing data from a Mitsubishi PLC FX3G using RS485.

FAQ: 2. What are the differences between FX3G-485-BD and FX3G-CNV-ADP -> FX3U-485ADP-MB modules?

Answer: - The FX3G-485-BD module is a direct communication module for the FX3G PLC, while the FX3G-CNV-ADP -> FX3U-485ADP-MB module requires more space as it needs to be added to the left of the PLC.

FAQ: 3. Why is the FX3G-485-BD module considered more suitable when space is limited?

Answer: - The FX3G-485-BD module is more suitable for limited space as it can be directly incorporated into the PLC without requiring additional space to the left of the PLC.

FAQ: 4. Are there any specific considerations to keep in mind when using the FX3G-485-BD module for Modbus communication?

Answer: - It is important to ensure proper configuration and setup of the FX3G-485-BD module to enable successful communication using the Modbus protocol.

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