Read more than 100 registers using modbus

[sophia3]

Hello Everyone, 
 

I downloaded modbus library and try to use modbus ethernet query to communicate with PLC. I found modbus can only read about 100 register one command but I need to read way more than 100 registers and record the data to a spreadsheet and export the final result as a csv file. I am really new to this field and wondering how can this be done ?(my guess is using while loop?)

[RavensFan]

Do multiple reads in series with each.  The first 100 registers, then the next 100, then so on.  Then you can combine the results to write to your CSV file.

[sophia3]

Hello Knight of NI,

Thank you for replying. I am wondering why cannot use a while or for loop?

[RavensFan]

I don't understand your question.  You'll have to show me an example of how you are thinking that a while loop is going to help you read more than 100 registers at a time.

[MarcoMauri]

Hi Sophia,

actually RavensFan is implicitly suggesting to use a while/for loop.

Do you need to read 10000 registers?

Run a for loop 100 times placing a modbus read of 100 registers inside.

Regards,

Marco

[RavensFan]

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@MarcoMauri wrote:

Hi Sophia,

actually RavensFan is implicitly suggesting to use a while/for loop.

Do you need to read 10000 registers?

Run a for loop 100 times placing a modbus read of 100 registers inside.

Regards,

Marco

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Not exactly.

You use a while loop to do repetitive readings of the same registers for an unspecified number of times.  You use a For loop to do repetitive readings of the same registers for a known number of times.

You can use a for loop for different registers, but you have to set it up correctly.  You'd need to use arrays that would define each group of registers that you can auto-index on that array so that each iteration of the For Loop will handle the different groups.  Of course modbus is returning data, so you need to figure out a way to send that data to different places since each group represents different data.

[Eric1977]

What have you tried? Please pose your code.

[sophia3]

Hi RavensFan,

Thank you so much for your advice. I am still working on the program. Since it's the first time I ever use labview, I did lots of readings for the past few days try to understand better. I will post my code as soon as I am done.

Sophia