Hello,

probably that protocol has it's own name, but you don't know it. Pls give us info about type of that flow meter and due this info we can find what's name of protocol. I have experience with some level meters that communicate via RS-485 bus, every device with own unique address of course, protocol not Modbus. In this case of flow meter I expect RS-4xx not RS-232, right?

Have you checked these FAQ's ?

How do you establish a MODBUS-RTU communication with STEP 7 (TIA Portal) for the SIMATIC S7-1200?

Another example:

Data Communication between S7-1200 and SENTRON PAC3200 via MODBUS TCP (Set 22)

Siemens S7-1200 Serial Communication

Hello,

As said by Mr Duris_I, it true that each device having it own protocol. In one project i worked with flow meters, but that was serial communication with free port protocol. If its same case then you need to understand the frame. for reading data , i think you need to provide some commands to flow meter then only it will provide the output . So may be with the help serial communication blocks  you can read the flow meter data.

Best way before checking with PLC, try to check with hyper-terminal for serial communication for understanding the data frame and length.

Unless until we don't know the detailed we cant comment.

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Hello,

ok, now you need look to documentation because of some eror checking system inside frames. You need to know how to count this CRC or other checks. Also we don't know this, it depends to manufacturer what type of check select. Other help you need?

Update: maybe I recommend to you use ARRAY OF BYTE than your exact structure fields. You can probably better handle with bytes.