Modbus TCP Input register

Hi

I’m struggling to understand the Modbus TCP Server block (TIA v17).

On my 1200CPU the modbus input register is automatically routed to IW and coils automatically routed to outputs(Q0.0+)??

My project is to add a Modbus module to an existing project for reading and writing some data, how can I prevent Modbus data to overwrite my existing inputs and outputs? as Q0.0 is already in use.

Hopefully I’m misunderstanding something :)

any help highly appreciated.

AutoGen_4279430

Hi

I’m struggling to understand the Modbus TCP Server block (TIA v17).

On my 1200CPU the modbus input register is automatically routed to IW and coils automatically routed to outputs(Q0.0+)??

My project is to add a Modbus module to an existing project for reading and writing some data, how can I prevent Modbus data to overwrite my existing inputs and outputs? as Q0.0 is already in use.

Hopefully I’m misunderstanding something :)

any help highly appreciated.

You are focussed on using the input and output registers. Have you configured any holding registers (data registers) yet? This way you can point to M-memory or a non-optimized DB. Perhaps you could show what you already have. (Place pictures in a single ZIP file)

Or perhaps you can have a look at a sample published by Siemens.
How do you program and parameterize Modbus/TCP communication between S7-1500 CPUs and S7-1200 CPUs?

Hi, and thank you for your reply.

My holding register is working as I expect. I'm using a DB for the holding-register data and I can send/receive data to/from my PC using a Modbus client program. 

But this DB (connected to MB_HOLD_REG) only contains holding-register data. Other registers like Coils are routed automagically to Q(outs). I guess this is the part I don't understand.

also, I found another topic on this forum: "Modbus TCP Coil R/W Address", It's also about mapping but I still don't see the hole picture unfortunately.

How can I map Modbus coil number 1 to my PLC's Q0.5?

or, How can I remove the link between Modbus coil number 1 from my PLC's Q0.1? 

same goes for input-register that are somehow mapped to my IW area.

AutoGen_4279430

Hi, and thank you for your reply.

My holding register is working as I expect. I'm using a DB for the holding-register data and I can send/receive data to/from my PC using a Modbus client program. 

But this DB (connected to MB_HOLD_REG) only contains holding-register data. Other registers like Coils are routed automagically to Q(outs). I guess this is the part I don't understand.

also, I found another topic on this forum: "Modbus TCP Coil R/W Address", It's also about mapping but I still don't see the hole picture unfortunately.

How can I map Modbus coil number 1 to my PLC's Q0.5?

or, How can I remove the link between Modbus coil number 1 from my PLC's Q0.1? 

same goes for input-register that are somehow mapped to my IW area.

The input and output registers are fixed to what they give you. Only position of the data registers are under your control. In theory it is possible to create your own code to handle Modbus TCP. But you may find that using some type of protocol converter is going to be less efforts.

You are welcome to use the "Support Request" link to speak to Siemens directly on matters where forum volunteers cannot assist. Do however make sure that you have studied the materials in the System Manual as the first responder's default is pointing you to that.