# CONTROL MODE -\> A PFC application is running **URL:** \ **Category:** CODESYS\ **Tags:** pfc200\ **Created:** [December 9, 2025, 2:30pm UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460 "2025-12-09T14:30:21Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![raphdmo](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@raphdmo](https://www.wago.community/u/raphdmo)\ **Post date:** [December 9, 2025, 2:30pm UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/1 "2025-12-09T14:30:22Z")
Hello, When I try to enter CONTROL mode on my 750-0881 using WAGO-I/O-CHECK 3, I receive an error message: “A PFC Application is running” How can I resolve this issue? Thank you ---
**Author:** ![JohnDitter](https://sea2.discourse-cdn.com/flex016/user_avatar/www.wago.community/johnditter/32/68_2.png) [@JohnDitter](https://www.wago.community/u/JohnDitter)\ **Post date:** [December 9, 2025, 10:19pm UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/2 "2025-12-09T22:19:38Z")
Stop the PLC in CoDeSys (Online → Stop) or set the mode switch to the middle position. The CoDeSys program must not be running when entering control mode in WAGO-IO-CHECK ---
**Author:** ![raphdmo](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@raphdmo](https://www.wago.community/u/raphdmo)\ **Post date:** [December 10, 2025, 6:40am UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/3 "2025-12-10T06:40:21Z")
Thanks for answering. Last questions if i may ? On the PFC, there is 6 modules of 16 Digital Input and 5 modules of 16 Digital Output. I’d like to control the switch of one lighting zone. 1. What is the différence between DI and DO ? witch one i may program ? 2. What librairies i may use within NODE-RED to control the light switch ? Thanks ---
**Author:** ![seweryn](https://sea2.discourse-cdn.com/flex016/user_avatar/www.wago.community/seweryn/32/1900_2.png) [@seweryn](https://www.wago.community/u/seweryn)\ **Post date:** [December 10, 2025, 7:10am UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/4 "2025-12-10T07:10:54Z")
Hello, 1. **DI** stands for **Digital Input** (reads a signal: ON/OFF), and **DO** stands for **Digital Output** (sends a signal: ON/OFF). With **DI** , you check whether a switch/sensor is active or inactive. With **DO** , you control something like a relay or a light switch. In practice, you read the DI and use that information to set the DO. For example, **press a button (DI) → turn on a light (DO)**. 2. If you just want to control a switch, **default node-red** **libraries** are sufficient enough. If you want to do something different please inform us. Hope this answers your questions. ---
**Author:** ![raphdmo](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@raphdmo](https://www.wago.community/u/raphdmo)\ **Post date:** [December 11, 2025, 6:02am UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/5 "2025-12-11T06:02:55Z")
Hello, Thank you very much for your responses, I’m starting to understand things better. If I understand correctly, the DI returns the status of my light (off or on), and the DO allows me to change this status. Therefore, I need to act on the DO. I have a WAGO 750-0881 that manages 8 modules of 16 DI and 6 modules of 16 DO. I would like to control the light using NODE-RED, but I don’t know which libraries to use. Could you help me? The DI is located in the 6th module, channel 2, and the DO that controls it is in the 2nd DO module, channel 15. Thank you. ---
**Author:** ![raphdmo](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@raphdmo](https://www.wago.community/u/raphdmo)\ **Post date:** [December 12, 2025, 7:47am UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/6 "2025-12-12T07:47:19Z")
Thank you for your response and your valuable help. With the MODBUS WRITE command, Node-RED requests an address. How can I find the address of DO Module No. 2 with Channel No. 5? Thank you ---
**Author:** ![raphdmo](https://avatars.discourse-cdn.com/v4/letter/r/41988e/32.png) [@raphdmo](https://www.wago.community/u/raphdmo)\ **Post date:** [December 12, 2025, 8:44am UTC](https://www.wago.community/t/control-mode-a-pfc-application-is-running/2460/7 "2025-12-12T08:44:49Z")
Thank you for your reply and your invaluable help. With the MODBUS WRITE command, Node-RED requests an address. How can I find the address of module DO #2 on Channel #5? Thank you