> For the complete documentation index, see [llms.txt](https://wiki.inels.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://wiki.inels.com/inels-bus/inels-design-manager-idm3/idm3-central-unit-configuration.md). # Central unit configuration *Part 3 — Reference.* `[☰]` → **CU configuration** *** ## 22.1 What this dialog does Everything here configures the **central unit itself** — its network, its clock, and how it talks to the outside world. This is separate from your project: it is the CU's own settings. Four tabs: **CU setting**, **Cloud setting**, **Third part setting**, **MQTT setting**. The dialog shows two columns: | Column | Meaning | | ------------------- | ----------------------------------------------------- | | **Project setting** | What your project says the CU should be configured as | | **Actual setting** | What the CU is actually configured as right now | When they differ, iDM3 asks you to choose — *"Please select the correct setting"*. Read both carefully before deciding: picking the wrong one can take a CU off the network. **Save to CU** writes the configuration to the central unit. When the CU's own configuration is pulled into your project you will see *"CU configuration was saved to project."* *** ## 22.2 CU setting ### Network | Field | Meaning | | ------------------------------------------ | ---------------------------------------------- | | **IP address** | The CU's address — this is what you connect to | | **Mask** | Subnet mask | | **Gateway** | Default gateway | | **IP address2** / **Mask2** / **Gateway2** | A second interface or address | | **DNS1** / **DNS2** | Name servers | > **Changing the IP address changes how you reach the CU.** Write the new address down before you apply it. If you lose contact, recovery means physical access to the unit. ### Time | Field | Meaning | | -------------- | ------------------------------------ | | **NTP server** | Time server the CU synchronises with | | **Time zone** | The CU's time zone | | **CU time** | The CU's current clock | | **IDM time** | Your PC's clock, for comparison | **Get the time right.** Every time program, heating schedule, and the astronomical module's sunrise and sunset calculation depends on it. A CU with the wrong time zone runs the whole building an hour out. ### Errors | Field | Meaning | | ------------------------------------------------------ | --------------------------- | | **Error code:** | The CU's current error code | | **Title:** / **Body:** / **ExtendedInfo:** / **Code:** | Details of the error | | **Reset error** | Clears it | Clear an error only after you have read it and understood the cause. See [Chapter 30](/inels-bus/inels-design-manager-idm3/troubleshooting-idm3.md). *** ## 22.3 Cloud setting | Field | Meaning | | -------------- | --------------------- | | **Mode:** | Cloud connection mode | | **User name:** | Cloud account | | **Password:** | Cloud password | Connects the installation to the iNELS cloud service, which is what phone apps and remote access use. > **Cloud credentials are credentials.** They are stored in the project. Treat `.elp` files containing them accordingly. *** ## 22.4 Third part setting The plain-text protocol that lets other systems talk to the CU. | Field | Meaning | | ------------------ | ------------------------------------------------------------------- | | **Port** | TCP port to listen on | | **Mode** | Protocol mode | | **Separator** | Character separating fields | | **Numeral system** | How numbers are represented | | **Event enable** | Whether the CU sends events as they happen, or only answers queries | Only devices marked **Add to iNELS 3 export** are visible over this protocol — see [Chapter 24](/inels-bus/inels-design-manager-idm3/idm3-external-systems-mqtt-modbus-cloud.md). **Turn on Event enable** if the other system should react to changes; leave it off if it only polls. Polling a busy installation is much heavier than receiving events. *** ## 22.5 MQTT setting | Field | Meaning | | -------------- | --------------------- | | **Mode:** | MQTT mode | | **User name:** | Broker username | | **Password:** | Broker password | | **Version:** | MQTT protocol version | MQTT lets the installation publish to a message broker — the usual route into home-automation platforms. **MQTT is one of the significant additions since the Rev19 manual**, which does not cover it at all. Supported units and firmware requirements are listed in `Advance/Documentation/BUS unit to MQTT.txt`, and summarised in [Chapter 24](/inels-bus/inels-design-manager-idm3/idm3-external-systems-mqtt-modbus-cloud.md). > **MQTT requires recent CU firmware** — from `02.97.02` for CU3-07M, CU3-08M and CU3-09M. Check [Chapter 25](/inels-bus/inels-design-manager-idm3/idm3-firmware-update-manager.md) before configuring it. *** ## 22.6 Before you change anything | | | | ------------------------------------------------ | ------------------------------------- | | **Write the current settings down** | Especially the IP address | | **Check Project setting against Actual setting** | Know which one you are keeping | | **Confirm the time zone and NTP server** | Everything time-based depends on them | | **Confirm firmware first for cloud and MQTT** | Both need recent CU firmware | | **Test the connection after saving** | Use **Ping test** in **Settings** | *** **Next:** [Chapter 23 — Connecting and uploading](/inels-bus/inels-design-manager-idm3/connecting-and-uploading-to-the-central-unit.md).