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

Mapping data items to global variables makes them accessible for application programs or Node-RED flows.

1. Prerequisite
2. You must add the data item to the Modbus RTU device.

1. Open the global variables view.
2. Create a new global variable.
3. Change the data type of the global variable to the appropriate data type. Choose from:
4. BOOL: Discrete Input or Coil
5. WORD: Input Register, Holding Register or Status Word
6. INT: Input Register or Holding Register, if the content can be meaningfully represented as integer
7. Change the I/O mapping of the global variable to the desired data item.

Adding a data item to a Modbus RTU server

Creating a global variable

Changing the data type of a global variable

Changing the I/O mapping of a global variable