# Adding a data item to a Modbus RTU slave

Data items are used to communicate with a Modbus RTU slave. Data items can be mapped to global variables.

1. You must add a Modbus RTU slave to your device configuration.

1. Open the device view.
2. In the device tree, double-click the slave 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 slave.
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 items.

9. ## NOTICE

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