Hello!

I have a S7-1200 with 4.1 firmware. I am trying to communicate with it using Modbus tcp.

Reading data from the PLC works fine. When I try to write, It sends back: Exception Response: Illegal Data address. The MB_server block's status changes to 8383.

During my attempts I found that if my MB_HOLD_REG db has 5 elements in it, I have to write all 5 of them to be able to write. If I write 1 the error comes back.

What do I need to change to be able to write only 1 element?

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Split from Tips and sample program for MODBUS TCP.

Hi

I'm having the excactly same problem with MB_SERVER and CPU firmware v4.1.

Is this a bug in the newest MB_SERVER ?

Hello,

look to previous Kaulquappe's post, there are important infos where is problem and how to solve it. Also look to TIA help for MB_Client instruction. Simply your Structure of DB and LEN parameter aren't same, maybe your DB isn't enough of space for your request of amount data.

Kaulquappe

Hello,
there seems to be a bug with V4.1....

If you use a STRUCT,  the length of it must meet MB_DATA_LEN. When you use an array, you can access e.g. 1 register out of 5.

Regards,
Kaulquappe

 I tried this, still cannot write to single register (06), only same LEN as in DB