Hello,

so again for sure, you want create own communication messaging with MB RTU protocol. Ok, your PDF is quite enough to start with problematic, also wiring and serial low level settings but I also recommend to check this site:

www.simplymodbus.ca

You can find there also some SW, applications what can be helpful to simulate devices. You can then better start to build some your PLC code. I need to say one important thing here, no one here will spend time to teach you, especially with this quite hard problematic. You need do all things by yourself and maybe ask here for some advices. One important tip, you can find all on this Forum, already made topics where some steps are already described, also with some code examples. generally, I expect that some standard examples with serial communication are enough for start, you need only change code to your needs but experience with communication tasks is very good to have.

Update: I want ask also, your comm module is not capable of MB RTU protocol? I see only few description of module, not exact order number and is clear that some modules are not capable for MB RTU protocol, only Freeport. In case your module is capable, you can select protocol inside module options and you're behined the problem.

Hello,

I think that you need look at some project (also many examples are on this Forum as FAQs) and check how it is programmed, modules configured. As I said, it is not easy in case you are starting now to do something like this.

Simply said again, what is inside your attached PDF, you need to understand to all things there because you can do nothing, problematic isn't easy.

Ok, at my shoes I try for first understand Modbus RTU protocol problematic, then start Master and Slave apps on PC and to some tests with data exchange. You can see data exchange bytes and you can then better understand how it is working. Then PLC programming is more clear.