Modbus RTU over TCP

[travijuu]

Hello, In our case, we need to read modbus device(irradiation sensor) over Moxa NPort 5150. Our device connected to Moxa via TCP and Moxa connected to irradiation sensor over RTU. Moxa is a bridge in here. We need to make RTU request over TCP. However, I couldn't find this feature in modbus-tk. How can I achieve? This feature exists in pymodbus by using framer=ModbusRtuFramer. You can check from the link.

https://stackoverflow.com/a/53431738/1645480

[sfcaracciolo]

I have same problem!

[travijuu]

@sfcaracciolo We created a simple working solution for this. You can try if you want.

from modbus_tk import utils
from modbus_tk.modbus_rtu import RtuQuery
from modbus_tk.modbus_tcp import TcpMaster

class RtuOverTcpMaster(TcpMaster):

    def _make_query(self):
        return RtuQuery()

    def _recv(self, expected_length=-1):
        response = utils.to_data('')
        length = 255
        while len(response) < length:
            rcv_byte = self._sock.recv(1)
            if rcv_byte:
                response += rcv_byte
            if expected_length >= 0 and len(response) >= expected_length:
                break
        return response

[sfcaracciolo]

@travijuu Thank you very much! It works excellent :)

[ljean]

Hello @travijuu Thanks for your answer and for this piece of code. Would you be ok to add it to the project? I let you create a PR if you are ok. Thanks Best luc

[pepe12311]

You would need an example of how to implement RTU over TCP communication. I have something done in tcp, but I have to modify it. Do you have an example? Greetings