Denilson Pegaia

Hi,

Here there are a sample project and some tips for implementation of MODBUS TCP with S7-1200:

1 - Pre requisites: STEP 7 >= V11 SP1 and S7-1200 FW >=2.1

2 – Documentation: the help on line of the blocksMB_SERVER and MB_CLIENTare the best way to get information about these blocks.

3 – Programming:

3.1 – On MODBUS TCP server

Use MB_SERVER instruction on the server:

Ports: as default you can use 502, however it is possible to use any ELSE ports already
used by S7-1200 (20, 21, 25, 80, 102, 123, 5001, 34962, 34963 and 34964).

Each connection needs a block call (with different instance DB, ID and port)

3.2 – On MODBUS TCP client:

Use MB_CLIENT instruction on the client:

Each connection need a block call (with different instance DB). ID and port must match with the server).

4- Status 7002 = meaning that there is no client connected.

 

 

NOTE: As from CPU FW4.0 / STEP 7 V13 SP1, the blocks MB_CLIENT / MB_SERVER was changed.

Now they are similar to S7-1500. The main difference is that now the connection definition is not made in block inputs but else in a external place (DB).

 

To create the connection reference DB, create a DB as usual, and as variable (any name) you should type (manually) as data type “TCON_IP_V4”.
The blocks online help shows the meaning of the variables.

I attached now two examples at one zip file: one for FW>4, other for FW<=3 (as original)

Hi,

 Is it not possible to communicate both write and read registers command from MB_CLIENT through the same port (502)?

br
Ohansen

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Split from Tips and sample program for MODBUS TCP.

Hello,
Yes the client can read and write registers over the same connection using port 502 at server side.
But you do it in sequence, means that you wait that the first request is done before you start another request.

Hi,

yes JKIM is right, if you try to start another request you will get an error if your first request hasn't finished.

Regards

how this is done in program, so use the same Mb client instance with the same connect parameter and change the mode , addresse , Length and PTR ??