Hello, I am currently utilizing the MobusFB library in order for Codesys to function as the client for a Mobdus TCP server. I have successfully tested the Mobdus TCP server using MBPOLL, for which I have obtained a license and verified the server's functionality. However, I am encountering an issue while attempting to read holding registers, as the eErrorID displays "Request not processed." I am curious as to why this is happening. Could it be necessary to activate an additional license on the USB dongle for this library to operate correctly? Upon monitoring in Wireshark, I can observe the CODESYS program establishing and maintaining the socket connection, yet no Modbus queries are being sent out to the network. Although I have been referring to examples provided by CODESYS, I find that they lack the necessary comments and guidance for someone new to this technology. Thank you for your assistance. Alfredo
Is it necessary for the CODESYS Modbus function to have a rising edge in order to initiate the query, and if so, are you able to provide it?
Thank you, Brian, for your comments and concern. I appreciate the feedback. I have attached a screenshot of my program, as requested. I am currently experiencing issues with the detection of licenses in my CODESYS program, which is installed on a PC with a USB dongle. Despite this, the program is not functioning in demo mode. Can you offer any suggestions on how to troubleshoot this issue?
Check out this helpful resource on CODESYS Forge for resolving issues with Modbus Client requests. Visit the CODESYS Forge Engineering forum for more information on Modbus Client Request troubleshooting.
Thank you, Parky, for your forum entry. I have gained some insights and will continue exploring further tomorrow. It's getting late here, so I'll pick up where I left off in the morning.
Hello Brian and Parky! I successfully converted a structured text sample program from Codesys' examples into ladder logic. Interestingly, there are not as many ladder examples available. I was able to make it work, although I had to incorporate a structured text box as I couldn't achieve the same functionality using ladder logic alone. I am eager to understand how to overcome this challenge. Feel free to take a look at the explanation below, and the project is attached for your review.
Hey Alfredo, it doesn't seem like a licensing issue as you have already validated the server's functionality. The "Request not processed" error might be due to incorrect register addressing or a communication problem between Codesys and the Modbus TCP server, which may cause requests to not reach or be processed. Try to double-check the register addresses you're attempting to read. Also, make sure the firewall isn't blocking the Modbus traffic. You're right about the CODESYS examples - they can be quite baffling when you're just starting. For better understanding, I'd suggest looking up some third-party tutorials and guides for CODESYS with MobdusFB, they tend to be more instructive. Good luck!
Hi Alfredo, It's unlikely your issue is down to a licensing problem with the MobusFB library. Generally, an issue like this points towards a problem in the code or in the configuration of the Modbus communication. The error message "Request not processed" could mean your Codesys client is sending an incorrect Modbus request, or the Modbus server is not configured to process the request type being sent. It might be helpful to check the following: Double-check the IP address and port in your Modbus connector configuration; make sure there are no firewall issues blocking communication; and ensure your Modbus read/write functions are using the correct addresses and data types. If possible, share some snippets of your code to give us a better understanding of your approach.
Hi Alfredo, it sounds like you're troubleshooting a complex issue. Good job on validating your Modbus TCP server with MBPOLL. Concerning your issue, it may not necessarily require an additional license. While eErrorID showing "Request not processed" could signify a number of problems, it often implies a communication issue between the server and client. Let's make sure that your CLIENT function blocks in CODESYS are correctly configured and that your requests are indeed routed to the correct network. Also, you could try to increase the timeout value if the requests are sent to a network with response delays. Keep in mind to make sure that your function blocks run cyclically in order for the requests to be processed. Furthermore, you're right, the examples often lack complete guidance; you'd get more familiar with them as you gain more experience. Don't hesitate to ask more specific question, as each of such scenarios might demand an individual approach. Keep going!
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Answer: Answer: The "Request not processed" error could indicate various issues such as incorrect configuration settings, communication problems, or licensing issues. It is essential to troubleshoot each of these potential causes to identify the root of the problem.
Answer: Answer: Activating an additional license on the USB dongle may or may not be necessary for the proper operation of the ModbusFB library. It is recommended to check the licensing requirements for the library and ensure that all necessary licenses are in place.
Answer: Answer: The lack of Modbus queries being sent out to the network could be due to configuration errors, communication settings, or other issues within the CODESYS program. It is advisable to review the program logic, network settings, and communication parameters to identify the cause of this issue.
Answer: Answer: If the provided examples by CODESYS lack the necessary comments and guidance for beginners, you may consider referring to additional resources such
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