Troubleshooting AB PLC Modbus Communication Problem - Need Help

Question:

Hello, I am currently working on programming an Allen Bradley PLC using RS Logix 5000 V20. I have been attempting to establish Modbus communication between the PLC and an RS232 to Ethernet converter. However, the PLC is not successfully establishing communication with the converter despite adjusting all parameters. If anyone has a solution or suggestions, please feel free to share them with me. Thank you.

Top Replies

If you're not specifying the processor model you're using, note that Rockwell processors, apart from ML1400, do not have built-in Modbus support. Previously, users had to buy a Modbus module from third-party vendors like ProSoft with the introduction of V20. However, Rockwell now offers an add-on instruction that can be customized for Modbus integration.

Hi there, first off, make sure the UART interface settings for your RS232 to Ethernet converter match those for your PLC's serial settings. That could very easily be the source of communication issues. If everything seems fine on that front, it might be worth checking your cables and connections, as a simple mechanical fault could also be causing the issue. Additionally, I recommend having a look at the Modbus configuration on the RS Logix 5000. Perhaps there's a problem with slave ID, start address, data length, or function code. Hope this helps you out, and good luck with your project!

It sounds like a tricky situation you're in. If you've already double checked your parameters, I'd recommend looking into the ControlLogix serial card configurations or consider obtaining a Modbus TCP module for your PLC. They're specifically designed to interface with Allen Bradley PLC's and could offer an easier route to establishing that communication link you're looking for. Also, remember to check your RS232 settings - baud rate, data bits, stop bits, parity, etc., as an incorrect setting might be causing the issue.

Hello, I've had similar communication issues before. You might want to consider checking the Ethernet/IP configuration, particularly the IP address settings within RSLogix. Ensure that the IP address matches with the converter’s IP. Additionally, for Modbus communication, Modbus TCP/IP protocol is often used for Ethernet paired devices - you may need to clarify if your RS232 to Ethernet converter supports this protocol. Lastly, make sure your cabling is correct and that you have the proper drivers installed.

Hey there, I had a similar problem a while back, and it turned out the issue was with my converter, not the PLC itself. Double-check whether your RS232 to Ethernet converter is compatible with your specific Allen Bradley PLC. Also, ensure the baud rate, data bits, stop bits, and parity of both the devices match exactly. I've found that Modbus communication sometimes requires precise settings. Don't forget to debug and monitor the packets sent/received using any software, such as Wireshark, to isolate the issue further. Hope this helps!

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Frequently Asked Questions (FAQ)

FAQ: FAQs:

Answer: 1. Q: What could be causing the Modbus communication problem between the Allen Bradley PLC and the RS232 to Ethernet converter? The issue could be related to incorrect parameter settings, compatibility issues, or wiring/connection faults. Double-checking the parameters and troubleshooting the connections could help identify the root cause.

FAQ: 2. How can I troubleshoot the Modbus communication problem between the PLC and the converter using RS Logix 5000 V20?

Answer: You can start by verifying the communication settings, checking the network configuration, monitoring data traffic, and using diagnostic tools within RS Logix 5000 V20 to identify any errors or inconsistencies.

FAQ: 3. Are there any common pitfalls or mistakes to avoid when setting up Modbus communication with an Allen Bradley PLC?

Answer: Some common issues include incorrect addressing, mismatched baud rates, improper wiring, inadequate power supply, or software configuration errors. It's essential to carefully review and validate each aspect of the setup to ensure a successful connection.

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