Hi,

What kind of Modbus communication do you want to do? Modbus RTU or Modbus TCP?

Regards,

Towome

Hello Darcer;

Our friend Towone asks a very judicious question: we need to know more about your project in rderto help you:

- for Modbus RTU communications with a S7-300 CPU, you will need a CP 341 and the Loadable driver Modbus RTU software and dongle (6ES7870-1AA01-0YA0), You will find 3 different models depending on the type of network connection:you ned for your slave(s).

-RS 232:: 6ES7341-1AH02-0AE0

- RS 422/RS 485:  6ES7341-1CH02-0AE0

- TTY (current loop):  6ES7341-1BH02-0AE0

This document will give you a step-by-step presentation on ow to connect the CP 341 either as a slave or as a master, including the program blocks required.

https://slideplayer.com/slide/4050376/

- for Modbus TCP, you need either a CPU with an integrated Profinet port (for example. a CPU 315-2PN/DP) of an additional Ethernet processor, CP 343-1 (all models will work, even a CP 343-1 LEAN). In both cases, you need additionalsoftware drivers, wither for the Profinet CPU or for the CP 343-1:

- How do you establish a Modbus/TCP communication from a SIMATIC S7-300/S7-400 and where can you find further information?

https://support.industry.siemens.com/cs/ww/en/view/22660304

 - SIMATIC SIMATIC Modbus/TCP communication using CP 343-1 and CP 443-1 (manual)

https://support.industry.siemens.com/cs/ww/en/view/103447617

If you want to discuss this issue fiurther, please give us a clear description of the hardware you will be using in your CPU rack, and the type and number of slaves/servers you will have in your network.

Hope this helps,

Daniel Chartier