# Adding a data item to a Modbus RTU server

Data items are used to communicate with a Modbus RTU server. Data items can be mapped to global variables. Each data item represents a request of the Modbus RTU client.

1. Prerequisite
2. You must add a Modbus RTU server to your device configuration.

1. Open the device view.
2. In the device tree, double-click the server you want to add a data item to.
3. In the Data items table, click the plus icon.
4. A new data item is added.
5. Name the data item uniquely within the scope of the server.
6. Set the function code of the data item.
7. Set the offset of the data item.
8. If more than one register shall be read or written, set the desired quantity of the data item.

9. If the request shall not be executed cyclically (default) but by trigger, you can create a trigger channel.

Adding a Modbus RTU server

Changing the function code of a data item of a Modbus RTU server

Changing the offset of a data item of a Modbus RTU server

Changing the quantity of a data item of a Modbus RTU server

Creating a trigger channel for a Modbus RTU request

Mapping a data item of a Modbus RTU device to a global variable