Is there a restriction within Connected Components Workbench or on Micro850s regarding the maximum number of Modbus messages that can be transmitted per cycle? Additionally, could there be a limitation on the number of write commands allowed? I was successfully operating 12 temperature controllers using Modbus, but upon adding two more, the additional controllers are not responding to write commands. Despite ensuring all settings are configured correctly and the PLC is able to read the current temperature, the new controllers are still disregarding write commands. I am curious if there is a restriction on the number of write commands that can be sent in a single cycle. Thank you.
I came across information stating that the limit is 16, but I was unable to locate the specifics to share with you. Are you utilizing Modbus TCP or RTU protocols? If using RTU, have you verified the termination is properly configured? What is the cable distance between the last two devices? Have you checked the baud rate settings and considered adjusting them if necessary?
I am working with Modbus RTU and have ensured that the termination is set up correctly. However, I have encountered a problem with communication when trying to operate more than 14 temperature controllers. Despite writing a separate program to address the controllers that were not responding, I suspect that I may be exceeding the message limit. In addition to sending set points, I am also controlling the on/off status of the controllers. Your assistance in resolving this issue is greatly appreciated!
When working with Modbus RTU, it is important to remember that communication takes place over a single serial line. In my opinion, it is best to send each message individually and wait for it to complete or time out before sending the next one. It has been noted that TCP is restricted to a 4x scan, which is relevant when dealing with these types of controllers.
Having to send each message individually can be quite a hassle, especially when managing multiple devices. Everything was working smoothly until now, so sending messages separately doesn't seem necessary. It seems like there may be a limit on the number of MODBUS messages that can be included in a program. I attempted to find information on this issue in Rockwell's knowledgebase and came across a relevant resource: example code for "Modbus Message Sequencing for Micro830 (Part of the Micro800 Family)." However, when I tried to download it, I received an isaxml file instead of the expected archive file. Do you have any suggestions on what to do with this file? The resource can be found on the Rockwell Automation website.
If you encounter a version error, make sure to have an "Exported" file ready for "Importing" to convert it to a newer version. This process is necessary if you are using version 22 of the software.
From my understanding and past experiences, there are restrictions within CCW or on the Micro850 regarding the maximum number of Modbus Messages per cycle. However, the limit isn't typically so low. What you're experiencing might be a bandwidth issue. Modbus isn't the fastest protocol out there and if you're polling too many devices or encoding too many write commands, you could be hitting the bandwidth limit rather than a hard-set limit on the number of commands. Before adding any more devices, I would suggest optimizing your poll rates or seeing if a network upgrade is possible to feature more bandwidth.
Your situation sounds quite puzzling! As far as I'm aware, Connected Components Workbench (CCW) or the Micro850 doesn't specifically limit the number of Modbus messages per cycle or the number of write commands. However, other factors may be causing your issue. Are all your devices on the same Modbus network? If the network is congested, it could cause slower communication or non-responding devices. Also, you may want to check if your additional temperature controllers have a unique Modbus address and whether there might be a physical wiring issue.
Based on my understanding and experience with the Micro850s, it doesn't explicitly limit the quantity of Modbus messages that could be transmitted per cycle or the number of write commands. However, it's worth noting that processing time and latency could indeed become an issue when you're adding more devices or if your write commands are complex. Also, sometimes each Modbus device itself can have restrictions on the number of messages it can handle. So, it could be your temperature controllers causing the issue rather than the PLC or Connected Components Workbench. You could try to stagger your write commands between multiple program cycles to see if that alleviates the issue.
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Answer: - Answer: There might be a restriction on the number of write commands allowed when using Modbus in Connected Components Workbench or on Micro850 PLCs. It is essential to check the specifications and documentation for any limitations on the number of messages that can be transmitted per cycle.
Answer: - Answer: The issue with new temperature controllers not responding to write commands could be due to a potential restriction on the number of write commands allowed in a single cycle. It is advised to verify the settings and configurations to ensure compliance with any limitations on write commands.
Answer: - Answer: To troubleshoot the issue of new temperature controllers not responding to write commands, double-check that all settings are correctly configured, and the PLC can read the current temperature from the controllers. Additionally, refer to the documentation to see if there is a restriction on the number of write commands that can be sent in a single cycle.
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