# Unable to Connect to 750-315 via Codesys Modbus RTU
**URL:** https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169
**Category:** CODESYS
**Tags:** codesys
**Created:** [August 26, 2024, 7:10pm UTC](https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169 "2024-08-26T19:10:00Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@jessp](https://www.wago.community/u/jessp)
#### Post date: [August 26, 2024, 7:10pm UTC](https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169/1 "2024-08-26T19:10:00Z")
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.
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.
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### Author:  [@jessp](https://www.wago.community/u/jessp)
#### Post date: [August 26, 2024, 7:29pm UTC](https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169/2 "2024-08-26T19:29:34Z")
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.
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### Author:  [@TomasD](https://www.wago.community/u/TomasD)
#### Post date: [August 28, 2024, 7:43am UTC](https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169/3 "2024-08-28T07:43:26Z")
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?
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### Author:  [@WagoKurt](https://www.wago.community/u/WagoKurt)
#### Post date: [September 25, 2024, 5:08pm UTC](https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169/4 "2024-09-25T17:08:46Z")
This is probably a wiring issue. Can you show how you have the RS485 half duplex coupler wired, and any termination resistors used?
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### Author:  [@WagoIcard](https://www.wago.community/u/WagoIcard)
#### Post date: [September 26, 2024, 12:04am UTC](https://www.wago.community/t/unable-to-connect-to-750-315-via-codesys-modbus-rtu/1169/5 "2024-09-26T00:04:42Z")
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:
