Hello,

    I am using openmodbus TCP communication with CPU315-2PN/DP with reference to the document

https://cache.industry.siemens.com/dl/files/304/22660304/att_57060/v1/modbustcppncpu_en.pdf

As per document, A maximum of 125 registers is possible for reading functions per message frame for Holding and Input Register. A maximum of 2000 bits is possible for Coils and Inputs.

In my application, i need to read  more than 125 register, presently 164 holding registers and it may increase later.

How i can read 164 holding register from the modbusTCP device?

Thank you

Hello,

you need do some state machine in your code to differ 2 independed requests, one for first able number of registers and next for rest of number amount devices. You can split both requests to numbers what is best for you to have good results. As example, you can read f.ex. for first 100 registers and at second request 64 registers.

Hi,

I program one request 

I don't know how to make second request.

I tried like

Which doesn't work.

Could you please help me to write second request?

Thanks

Hello,

very sry, from your code isn't so much clear what is your intention to do. Basically, use of some time/timer to differ different polls is not good idea. You need simply do that state machine better, simple stat like BYTE value and set it to some states as steps are defined, as you need. Then you can be sure where you are at actual time (byte value correctly set) and you can do better functionality. Your code is only as is, without to see actual values inside and then is impossible to recommend something. I've recommended some amount of devices read for first and rest as next but your idea is looks like different. really hard to help, especially if we can see that your steps are like hit and hope for not miss.