Modbus device not working with Labview, but works with Python.

[henk1000]

Hello,

I have trying to connect a modbus device using Labview but it does not work at all. My previous application uses Python (pymodbusTCP) and it works well.
I have gotten the errors 56 and 66. I suppose it can not be a network problem because it works well with a python script. The address and port is all the same.

Thank you.

[ZYOng]

Are you using NI Modbus Library Toolkit for LabVIEW?

You can Performing a Good NI I/O Trace Capture for Debugging/Troubleshooting to debug the data sent and received

[henk1000]

Hi Zyong,

Thank you for replying. I have used so far two libraries, NI Modbus Library and Plasmionique Modbus Master. None of them has worked.
To begin I just would like to read the holding registers from the device.
I have been using Labview 2024 Q1.

Best,

Henrique 

[LVNinja]

Can you share your code for version 2020 ? 

[henk1000]

I have been using Labview version 2024 Q1.

[altenbach]

A picture is not code! Why are there terminals without label?

Do you really want to do two things (reading/writing) in parallel with no clue what happens first?

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@henk1000 wrote:

I have been using Labview version 2024 Q1.

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[henk1000]

I have tried also only reading and the result was the same. The program is quite simple so I find it not necessary to post it. If it is really necessary I can post it.

[altenbach]

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@henk1000 wrote:

The program is quite simple so I find it not necessary to post it.

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Again, a picture of code with unlabeled terminal and coercion dots (e.g. your "register to write" should not be U8) raises a lot of red flags. We also can't tell any of the wire values. Is LabVIEW allowed to use the network? Do you really think you should branch the wire?

(disclaimer: I don't do modbus and I am not familiar with your toolkits. Hopefully somebody else will help.)

[henk1000]

Hi,

This is the code.

[ShockHouse]

The biggest gotcha I usually see is the address, from the NI Modbus documentation:

So I would check to make sure the register you want to read is correct.

Usually error 56/66 are a a result of the remote application closing the connection. Which could likely happen if the address, or amount of bytes are wrong.