to 天天工控,Access to the
Modbus slave manual here
Good point, if your Rx LED is blinking, it shows that the electrical connection between the 2 units is good; doesn‘t mean that it is validated for the protocol though, but it is better than no LED at all.
Now for some questions:
How did you parametrize the CP 441-2, how is it setup.
Did you create a PtP connection in Netpro? The connection ID number is required in the communication FB180 Parameter "ID")
The properties of the CP 441-2 have been correctly setup for Modbus (baudrate, parity...) you say The parameters have been correctly downloaded to the CPU? (Just checking...)
Please show a screencapture of your FB180 call in OB1, we probably need to see how it has been setup to help you out.
Have you inserted a rising edge on the input parameter "CP_Start" in OB100, to initialize the CP in the CPU startup?
Which Modbus function codes (and lengths) are requested by the master, and how did you associate the native S7 addresses to the Modbus (Modicon) addressing for the different Modbus functions?
The manual suggested above has some information on these (and many other) aspects of setting up a CP 441-2 as Modbus slave. And there are chapters on the diagnostics of the CP 441-2, starting with LEDS decoding, use of the diagnostic buffer of the CP (through the Onlive view of the Hardware Config editor) and the Systat message area of the instance DB of FB180. But we also will be here to give a hand, so come back to the forum with any other questions or clarifcations.