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Modbus TCP Multiplexing example or tips

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Hi All,

I'm battling a bit with modbus TCP multiplexing and missing messages.

I have a Vision 430 with 5 VFD's. 

Some of the time, the messages go through quite fine. I send a PHR, the action is taken and the MODBUS status message is 0 - all good.
Some of the time, I send a PHR, the action is taken but the status message shows as 4, then 5(timeout) but the VFD still receives the message and carries it out.
Sometimes I send a PHR and nothing happens.

Does anyone have an example of a successfully completed modbus TCP multiplexing that I can take a look at? Or perhaps any tips as to where I can look. 

My code looks a lot like the V280 Example with the exception of a connect at the beginning of each command and a disconnect after - sample attached.

Many thanks!

AF Example.vlp

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  • MVP 2023

I haven't looked at your code yet, but I presume you are connecting and disconnecting for each VFD communication. If so, you need to provide surprisingly long wait times between each operation - on the order of at least a couple of seconds, if not more. If the total cycle time becomes too long for your application, you can connect to 2 or 3 at a time since you have 4 sockets available.

A better option would be to use the V700, since it has 8 sockets, so that you can maintain communication with all 5 simultaneously and continuously.

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