# Creating a trigger channel for a Modbus RTU request

By default, a request of the Modbus RTU client to the Modbus RTU server is executed cyclically. For an edge-controlled triggering of the request, you must add a trigger channel to the data item of the Modbus RTU server. After mapping the trigger channel to a global variable in the real-time application, the request will be triggered by a rising edge of the global variable.

1. Prerequisite
2. You must add a data item to the Modbus RTU server.
3. You must create a global variable (BOOL).

1. Open the device view.
2. In the device tree, double-click the server whose data item you want to edit.
3. Select the data item you want to change.
4. Double-click the Trigger channel text box.
5. In the text box, enter a name for the trigger channel.
6. Press Enter.
7. The trigger channel can be mapped to a global variable now.
8. Open the global variables view.
9. Select the global variable you want to map to the trigger channel.
10. Double-click the Mapping list box.
11. In the drop-down list, select the trigger channel.
12. Press Enter.

1. The request is executed with each rising edge of the global variable.