# Modbus rtu problem **URL:** \ **Category:** CODESYS\ **Created:** [October 8, 2025, 12:33pm UTC](https://www.wago.community/t/modbus-rtu-problem/2347 "2025-10-08T12:33:20Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![hkn\_blt](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hkn\_blt](https://www.wago.community/u/hkn_blt)\ **Post date:** [October 8, 2025, 12:33pm UTC](https://www.wago.community/t/modbus-rtu-problem/2347/1 "2025-10-08T12:33:20Z")
Hello, when I want to read data from Modbus RTU, I can read it using function blocks. However, I can’t read it by adding it as a tree from the left side. We often encounter this problem when reading from energy analyzers. Has anyone encountered this before? ![Screenshot_1](https://us1.discourse-cdn.com/flex016/uploads/wago/original/2X/8/83f67c658d61d9d04c4516f2515368a9881206e3.jpeg) ---
**Author:** ![WagoIcard](https://sea2.discourse-cdn.com/flex016/user_avatar/www.wago.community/wagoicard/32/1508_2.png) [@WagoIcard](https://www.wago.community/u/WagoIcard)\ **Post date:** [October 14, 2025, 2:39am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/2 "2025-10-14T02:39:50Z")
Is the COM port already in use ? What port are you using (integrated serial port or the 750-65x ? ---
**Author:** ![hkn\_blt](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hkn\_blt](https://www.wago.community/u/hkn_blt)\ **Post date:** [October 14, 2025, 4:57am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/3 "2025-10-14T04:57:57Z")
COM port is not used. Integrated port products.and I set it as Rs485 from the settings. ---
**Author:** ![rahooldas](https://avatars.discourse-cdn.com/v4/letter/r/0ea827/32.png) [@rahooldas](https://www.wago.community/u/rahooldas)\ **Post date:** [October 14, 2025, 7:42am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/4 "2025-10-14T07:42:04Z")
1. First thing to check is if your able to read any device using the Modbus Configurator. this will ensure all settings are correct . i usualy use a rs485 to USB cable , along a modbus slave simulator in the PC. 2. Check the settings in all the 3 lines here ![image](https://us1.discourse-cdn.com/flex016/uploads/wago/original/2X/e/e49b5749a3ca5ccc40c0822adc60af4410a913df.png) 3. what is the error you get when using the modbus configurator. 4. Sometimes you need the 120ohm resistor to be in place. usualy this should be common for the configurator and FB method, only once i had such a issue. ---
**Author:** ![hkn\_blt](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hkn\_blt](https://www.wago.community/u/hkn_blt)\ **Post date:** [October 15, 2025, 9:57am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/5 "2025-10-15T09:57:58Z")
I’m doing everything you said here. But I can’t get any results. It always gives a timeout error. However, when I use FB with the same settings, there is no problem. ---
**Author:** ![WagoKurt](https://sea2.discourse-cdn.com/flex016/user_avatar/www.wago.community/wagokurt/32/11_2.png) [@WagoKurt](https://www.wago.community/u/WagoKurt)\ **Post date:** [October 15, 2025, 2:58pm UTC](https://www.wago.community/t/modbus-rtu-problem/2347/6 "2025-10-15T14:58:02Z")
Maybe this is an obvious question, but you are disabling the Modbus\_Read POU when testing the MB RTU configurator? Only one master can bind to the serial port at a time. ---
**Author:** ![hkn\_blt](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hkn\_blt](https://www.wago.community/u/hkn_blt)\ **Post date:** [October 16, 2025, 5:01am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/7 "2025-10-16T05:01:50Z")
> [@WagoKurt](#): > > i bu bariz bir soru olabilir, ancak MB RTU yapılandırıcısını test ederken Modbus\_Read POU’yu devre dışı mı bırakıyorsunuz? Seri porta aynı anda yalnızca bir ana cihaz I am trying it only with the configurator without creating the function block, but it does not read it.It doesn’t do this all the time. While it reads some devices, it doesn’t read them with the configurator. ---
**Author:** ![Thruser](https://avatars.discourse-cdn.com/v4/letter/t/d26b3c/32.png) [@Thruser](https://www.wago.community/u/Thruser)\ **Post date:** [October 16, 2025, 7:13am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/8 "2025-10-16T07:13:13Z")
Hi, when you are using the configurator, do you have set the serial port in WBM to RS-485? I think, when you are using the function blocks then the WBM settings are overwritten, but when using the configurator the WBM setting ist used. ---
**Author:** ![hkn\_blt](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hkn\_blt](https://www.wago.community/u/hkn_blt)\ **Post date:** [October 16, 2025, 11:32am UTC](https://www.wago.community/t/modbus-rtu-problem/2347/9 "2025-10-16T11:32:38Z")
> [@Thruser](#): > > m fonksiyon bloklarını kullandığınızda WBM ayarları üzerine yazılıyor, ancak yapılandırıcıyı kullandığınızda WBM ayarı kullanılıyor. yes. I set the port from WBM to RS485.