# Communication Modbus RS485 **URL:** \ **Category:** CODESYS\ **Tags:** pfc100, codesys\ **Created:** [January 23, 2026, 4:14pm UTC](https://www.wago.community/t/communication-modbus-rs485/2536 "2026-01-23T16:14:45Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![dhia](https://avatars.discourse-cdn.com/v4/letter/d/5f8ce5/32.png) [@dhia](https://www.wago.community/u/dhia)\ **Post date:** [January 23, 2026, 4:14pm UTC](https://www.wago.community/t/communication-modbus-rs485/2536/1 "2026-01-23T16:14:45Z")
Hello everyone, I am working on a **serial RS-485 half-duplex Modbus RTU** communication. I am using a **WAGO 750-8112** with **CODESYS 3.5**. For the serial interface, I used a **MOXA UPort 1150** (USB-to-serial converter for simulation): - **Pin 3 (R+) of the MOXA** connected to **pin 1** of the **WAGO 750-1652** card - **Pin 4 (R−) of the MOXA** connected to **pin 5** of the **WAGO 750-1652** card I am communicating with a **Modbus simulator** (simulator name). Unfortunately, I am unable to establish communication with the simulator, whether through I/O check or the API program. On the **750-1652** card, both **LEDs A and E are solid green** , while all other LEDs are **off**. Do you have any recommendations or suggestions to help me resolve this issue? API Code: ![image](https://us1.discourse-cdn.com/flex016/uploads/wago/original/2X/0/065e543df1f31d2aed16333840a141224b2ccfd0.png) ---
**Author:** ![AdamReeve](https://sea2.discourse-cdn.com/flex016/user_avatar/www.wago.community/adamreeve/32/59_2.png) [@AdamReeve](https://www.wago.community/u/AdamReeve)\ **Post date:** [January 23, 2026, 5:53pm UTC](https://www.wago.community/t/communication-modbus-rs485/2536/2 "2026-01-23T17:53:41Z")
In your function block call you have I\_Port := COM1 COM1 is the built-in DB9 port on the 750-8112. To use the 750-1652 module, replace COM1 with the module’s name in the project tree. i.e. I\_Port := \_750\_1624\_24 ---
**Author:** ![dhia](https://avatars.discourse-cdn.com/v4/letter/d/5f8ce5/32.png) [@dhia](https://www.wago.community/u/dhia)\ **Post date:** [January 28, 2026, 3:32pm UTC](https://www.wago.community/t/communication-modbus-rs485/2536/3 "2026-01-28T15:32:09Z")
Thank you for your feedback, I was able to retrieve data between a simulator installed on a PC and my API via Modbus RS232. Now, I’m trying to communicate serially between a Schneider TRV00210 module and my API using Modbus RS485 half-duplex. To get started, I’m first communicating with a single device. [Compact NSX Modbus User manual 2009](https://www.studiecd.dk/pdfs/all/lv434107_modbus_user_manual.pdf?utm_source=chatgpt.com) The LEDs on board A and E are steadily green, B is blinking, and the rest are off. Does this mean I have a problem with my slave device? For uiReadAddress, should I use hexadecimal or decimal format? ![image](https://us1.discourse-cdn.com/flex016/uploads/wago/original/2X/3/3c6b04f75a5e43ec13bdf312431ac27a67777939.png) Regarding the wiring part: ![IMG_20260128_164943](https://us1.discourse-cdn.com/flex016/uploads/wago/original/2X/d/dff50c289c59ead61a74aa8042076b40ea0742bb.jpeg) ---
**Author:** ![Thruser](https://avatars.discourse-cdn.com/v4/letter/t/d26b3c/32.png) [@Thruser](https://www.wago.community/u/Thruser)\ **Post date:** [January 28, 2026, 8:52pm UTC](https://www.wago.community/t/communication-modbus-rs485/2536/4 "2026-01-28T20:52:20Z")
Hi, with RS-485 Half Duplex only terminals 1 and 5 are required on 750-1652. Possibly also 3/7 for ground an 4/8 for screen. 2 and 4 are unused. What is connected there? For LEDs: E=on, F=off, G=off means RS-485 Half Duplex mode. B blinking means sending. C is blinking when receiving. See manual 100 and 16#64 is the same, sometimes it is easier to use or understand one format or the other. ---
**Author:** ![dhia](https://avatars.discourse-cdn.com/v4/letter/d/5f8ce5/32.png) [@dhia](https://www.wago.community/u/dhia)\ **Post date:** [January 29, 2026, 10:43am UTC](https://www.wago.community/t/communication-modbus-rs485/2536/6 "2026-01-29T10:43:18Z")
Hello, Thank you for your response, You have confirmed my suspicions. I will check with them why they wired terminals 2 and 4.