Hello,

I'm currently having a hard time establishing a connection/retrieving any register data from my slave device. I think issue might be in the initial Configuration/Modbus_Comm_Load portion. I've read through the "How do you establish a MODBUS CONNECTIONS" article, so I have done some initial reading and research on the topic.  

( https://support.industry.siemens.com/cs/document/47756141/how-do-you-establish-a-modbus-rtu-communication-with-step-7-(tia-portal)-for-the-simatic-s7-1200?dti=0&lc=en-WW )

Question: Based on the above article, we are suppose type in the instance data block of the master or slave block (master in my case) in the MB_DB parameter of the Modbus_Comm_Load block. Yet, when I do this the address gets highlighted in RED and I get a " the data type Modbus_Master of the actual parameter does not match the data type P2P_BASE_MB of the formal parameter".

Any insight on what I'm doing wrong??? I'm sure I might have overlooked something.

Thanks, in advance

SCR 8893

Found the issue ... for whatever reason tia portal v13 has two Modbus folders ... one named "Modbus (RTU)" the other "Modbus". Both folders have similar function blocks, however when I use the function blocks from the "Modbus" folder and place the instance datablock of my MB_MASTER in the MB_DB input of the MB_COMM_LOAD function block I do not get an error.

Does anyone know why this is ? Thanks, in advance.

Sergio

The S7-1200 system manual explains the difference in section 13.5.3.1:

● Modbus RTU instructions (Page 958): These Modbus RTU instructions provide all of the functionality of the legacy instructions, plus the ability to connect to PROFINET and PROFIBUS distributed I/O. The point-to-point instructions allow you to configure the communications between

FYI, the legacy instructions are MB_COMM_LOAD; MB_MASTER; MB_SLAVE. The 'new' versions are Modbus_Comm_Load; Modbus_Master; Modbus_Slave.

Did you find what is problem? Now i have that problem

Efrem95

Did you find what is problem? Now i have that problem

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Thanks for understanding and meeting us half way.

I found that info in manual.

True, the histrory has no records where lies th legacy and where lies the fresh.

Although... if judging on the block's images provided in manual the legacy has a tiny extension triangle and the fresh is without one. Also similar blocks have different names.

BR

The original issue in this case was the error when adding Modbus_Master_DB to the MB_DB input of the Modbus_Comm_Load_DB: 

 " the data type Modbus_Master of the actual parameter does not match the data type P2P_MB_BASE of the formal parameter". 

The thing is the Modbus_Master_DB data structure has a member of type  P2P_MB_BASE.That member is accepted by the Modbus_Comm_Load_DB block.

step by step (see picture):

1. Add Modbus_Master_DB to the project

2.Locate MB_DB member in the Modbus_Master_DB structure.

3. Drag it into the MB_DB input of the Modbus_Comm_Load_DB block.