(Beginner) Challenge to cascade Modbus slaves

[gunji-m]

Hello everyone,
First of all, let me express my gratitude to the developers who provide pymodbus.
Thank you.

I am a beginner both as a programmer and as a pyModbus user.
I apologize if my question is a duplicate.

My questions are as follows:

Q. In ModbusTCP, how should I write Python code and set the register map in the following configuration?

ex:) Master(Mac) → Slave(RasPi-a) → Slave(RasPi-b)...

Currently, we have completed the basic learning of creating a client request on the Mac side and receiving register values ​​via ModbusTCP, as shown below.

Mac (host :192.168.xxx.2)
↓
↓ protcol :ModbusTCP
↓
RasPi(
host :192.168.xxx.3
GPIO :DHT-11 sensor
)

P.S.ーーーーーーーー
Ultimately, I would like to try a network configuration like the one below.

Mac (host :192.168.xxx.2)
↓
↓ protcol :Modbus TCP
↓
RasPi-a(
host :192.168.xxx.3
)
↓
↓ protcol :Modbus RTU
↓
RasPi-b(
port :tty~~~
GPIO :DHT-11 sensor
)
↓
↓ protcol :Modbus RTU
↓
RasPi-c(
port :tty~~~
GPIO :something sensor
)
↓
↓ protcol :Modbus RTU
↓
any units ...

[janiversen]

Simply use the slave ids for the slaves below the tcp modbus server.

pymodbus client is pretty simple tu use, see the examples I assume you have the tcp server software if not you are in for a bigger challenge

[gunji-m]

Thank you for your reply.
I didn't have any TCP server software on hand, so I looked at the pymodbus documentation and source code and created a simple client.py to get started.

As an image, prepare something similar to the contents of client.py (for example, as a function) in the source of server.py, and set the function's operating condition to proceed to the next step if it does not match its own slave ID. ...Is it something like that?

Thank you for your kind advice.

[janiversen]

It is something like the serial forwarder example, that sadly have a number of restrictions. We know how to make a real serial forwarder, but do not currently have time to make the example.

In general it sounds like you would benefit from reading our documentation and download the examples.

[janiversen]

And just to answer your question, no it is a lot more complicated than just adding a function call in the server. A proper serial forwarder needs to be done at framer level, so a proper solution is to interconnect a tcp-server framer with n serial-client framers.....this is something you cannot do with the pymodbus Api, but only by adding code to the library.

[gunji-m]

Thanks for the ideas and advice!

I'll try again based on your advice!