Unable to Connect to 750-315 via Codesys Modbus RTU

Hi all,

I am attempting to use the Control Win V3 soft PLC to control a WAGO 750-315 remote I/O system via modbus RTU communication. I am struggling to connect to the device.

I have setup my devices as shown in the images below. I have verified that my com port settings are correct as I am able to connect/control using modbus simulator software with these settings. Additionally, I have updated my settings to 485 using the PLC shell. I have also set “always update variables” to enabled (1). The slave device is still shown with an orange triangle.

image

I have also tried connected to a modbus master simulator program as instructed in a tutoriall, but then there is also an orange triangle shown on the COM port.

Status of modbus serial device status show as “Not Running.”

Any ideas? Do I need to use an OPC UA server? I am just wanting to read/write inputs to this remote I/O using codesys. I have been able to do so using other programs.

UPDATE: I was able to connect to both a modbus slave program and the codesys COM port simultaneously using a virtual serial port splitter, but unfortunately that did not remove the orange triangle on the salve device, only the COM port.

As far as I understand, this is Coupler, therefore I don’t see Ethernet for OPC UA here. When connecting light bulbs to the Coupler, do the modbus indicators show anything?

This is probably a wiring issue. Can you show how you have the RS485 half duplex coupler wired, and any termination resistors used?

Hello, What connector are you using ?
A simple DB9 connector and some wire solder to it, or a RS485 DB9 connector ?


The ground (G) is not required for 422 and 485.

RS-485 need some resistance and more connection that we think for the polarization of the line, here is a diagram of the 750-960 connector: