Modbus controls

Hi guys, I'm fairly new to Modbus and I'm having an issue with turning a device off an on over a modbus tcp connection over ethernet. This is a very simple code, so I'm not sure where the problem is or why it is behaving the way that it is behaving. I wrote a similar program to read the values from a nearby address and it is working perfectly. The "0" address is the control word address. 1150 is the stop/get ready command, while 1151 is the start command. Upon executing the code once, the vfd's start up just as they should and they are set to the appropriate hertz value, as they should. However, after changing the hz value and running the code once more, the vfd's turn off. Then, if i run the code again, they will turn back on and change to the hertz that I have set. In other words, on every odd run of the code, they are on and functioning, while on every even execution of the code, they will turn off. I understand that the issue is probably with the 1150 and 1151 write commands, but I can't wrap my mind around why this is. Any help at all would be greatly appreciated. Thank you!
Attachments:
multiple write not working.vi ‏29 KB

BoKnows wrote:
If I'm understanding your original post correctly, everything executes as you expect if you only try to work with one vfd. Is that correct?
If so, have you tried testing with each of the vfd's individually to make sure they're all responding? If all four pass, I'd have a hard time suggesting the device is the issue. That would show each device responds to the commands. It would also show the modbus library is performing as expected.
The next piece would be to debug the code to determine why we are seeing the odd/even behavior we are now.
Since yesterday, I have tried controlling all four vfd's and all four are functional. I was able to split up the labview code into two different true/false cases which is essentially just an on/off switch between the 1150 and 1151 commands and everything works perfectly. However, my problem now is that I need to be reading the speed from one address constantly and then writing the speed to a different address whenever I choose to. In order to do this, I would need to be able to run it in a while loop, but I think that this causes a problem. I'm not sure if modbus reading and writing has a problem with being run continuously since I am very new to it, but I can't imagine that it wouldn't be able to do this. I will post my code so you can see what I'm talking about. Anyways, my read code works flawlessly on its own. When I try to run my write code, however, they both work fine for a few seconds, maybe up to ten at the very most. After this, I get a labview error code 60 that says
"Error 60 occured at TCP Open Connection in TCP Master.lvclass:Initialize Master.vi->Modbus Master.lvclass:Initialize.vi->API Main.lvlib:Create TCP Master.vi->true false write.vi
Possible reason(s):
Labview: The specified port or network address is currently in use. Select an available port or network address."
Now, I figured that this would maybe be due to running two different labview codes at the same time which were trying to access the same device at the same time via ethernet, so I only ran my write code without having the read code running and I got the exact same problem, so I know that the problem lies in the write code. I am completely stuck and don't really know what to do, so any help from anybody would be greatly appreciated.

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