marcunni24 Posted February 12, 2018 Report Share Posted February 12, 2018 Dear all, I'm programming an application on a SM43-J-R20 PLC+HMI. I've added a V100-17-RS4X card, in order to use RS485. I've succesfully implemented Modbus RTU communication with a Frequency Drive. The thing is, I need to communicate with 11 of them. The ladder logic so far uses the Modbus function blocks, as can be seen on the Modbus webinars on Unitronics page. That is, I SET a variable (ex:MB0) , which is used for enabling the "function 06 Modbus" block (preset holding register). At the output of the block, I RESET that same variable, ensuring the block gets executed. At the same time I reset MB0, I SET a new variable (MB1), which in turn is used for enabling the second Modbus block. This creates a sort of "continuous broadcast" to the drivers (which, If they don't receive a command in a certain time, trigger a failure). When the last block gets executed, the sequence restarts, The question is, when I try to send a Stop command to one driver (for example), it takes an awful amount of time to execute the order (30 seconds or so). I believe I may have a conflict between some of this blocks being executed at the same time. Is there a tutorial or an example where I can see how to succesfully implement Modbus communication with several slaves at the same time? Thanks for the support. Kind regards, Martin Quote Link to comment Share on other sites More sharing options...
Gabriel Franco Posted February 13, 2018 Report Share Posted February 13, 2018 Several slaves at the same time is not posible using Modbus RTU using RS485 network. You must add a short time between Modbus read/write blocks in order to allow each slave to process and respond back and also to allow PLC to process its buffer. I´ve used delay timer as short as 50 ms Keep in mind that, if any slave does not respond immediatly, PLC will wait as much time as you set time-out before polling the next slave. This can be add more time than you expect between whole cycle. My suggestion: if you really need stop a device quicker, use digital outputs instead of Modbus commands. 1 Quote Link to comment Share on other sites More sharing options...
marcunni24 Posted February 16, 2018 Author Report Share Posted February 16, 2018 Gabriel, Thanks for your prompt response. I've added the delay, and now it's working properly. Regards Martin Quote Link to comment Share on other sites More sharing options...
Gabriel Franco Posted February 17, 2018 Report Share Posted February 17, 2018 Martin, thanks for letting us know your problem has been solved Quote Link to comment Share on other sites More sharing options...
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