Hello,

ok, lets go to your questions.

1. I have installed the specific small module inside the plc

ok, what module and where in PLC?

2. when i programming it with tia portal v16...

for first it is important to know what role plays your PLC (Master/Slave). What blocks you've set in your prj?

3. activates alarm that says 'invalid data lenght'. Is there  any option that has to be activated in order to play?

where your alarm is vissible? What cfg you did to have correct set of specific parameters depended to PLC Modbus functionality?

There are help about use of Master or Slave Modbus RTU driver with CP341 what is general help to Simatic Manager and also to TIA portal prj. It is expected that proper blue Dongle cartridge need to be also inserted at back side of CP341 in case of use of Siemens block solution.

Hello,

look to my previous post where I describe cleary where you need pay attention - CP341 Master/Slave driver problematic. I see your problem here, with no correct blocks used as is described in my mentioned documentations. You need use P_SND_RK and P_RCV_RK blocks and need configure cfg block correctly with parameters as you need. This system of cfg is little bit different to your mentioned system blocks for MB RTU functionality.

Here is recommended documentation what can help you: 

S7-300/400 Loadable driver MB RTU Master 

Sry, what I see now from your screenshot as block cfg. This is not relevant as topic problematic but only as tip for you generally. What is reason to cut EN input of block? Generally this is not recommended only in case you know what you do, simply is recommended to have this input without any condition. For block handling, you have there other important input parameters.

Important cfg on CP341 HW module: in case of use Master functionality, you need set this option under Protocol option field.

Hello,

looks like you didn't read my link documentation, all is described there in Function Code part. There is clear described how to define specific DB where all typical parameters depended to used MB FC code are described. This DB has typical 6 Bytes long so you can easy point in SEND block to this defined DB and set LEN as 6, because BYTE data type system is here used. Look at that structure of DB, each FC code different part include clear description and also this DB what it can contains as parameters due this specific MB FC. Then driver build standard MB RTU frame due this your defined structure and that's all. Why I include link with important documentation and it is not readed by users. I know, is simple in this times ask for exact solution and not do some research and do tests, learning. Documentation is first important thing what you need to use and read, do tests.

 Hello,

Savage123

i have read the instructions that you said yesterday.

The problem i think is that i configured only the receive function.

The write i havent configured it yet.

Best Regards

 eeeeeehm very sry but I don't understand to your statement. Only receive configured? And what functionality you then expect if you didn't configure all what is required as documentation shows? From your previous post is clear you also configured blocks and parameters.