5.4.4 GATT Operation on Client Role

Before performing the characteristic access operation, the user must have basic knowledge about GATT service. For more details on GATT service basic knowledge, refer to 9 Appendix A. Bluetooth Low Energy Fundamentals.

To address server services, the first letter of the characteristic access commands is S; to address client services, the first letter of characteristic access commands is C.

Bluetooth SIG adopted a group of public service specifications serving as the basis of interoperability between devices. A 16-bit short UUID is assigned to all services and characteristics in the public service. Any user-defined private services and their associated characteristics have 128-bit long UUIDs. To optimize the handling of 128-bit characteristic UUIDs, Bluetooth provides the method of using 16-bit handles.

The GATT server generates the handles. The GATT client reads the handle values as part of the service discovery process when connecting to the GATT server. The RNBD451 module provides commands to read and write both server and client attribute values by using these handles. To address a characteristic by its handle, the second letter of the characteristic access commands must be H. To read a characteristic, the third letter of the characteristic access commands is R; to write a characteristic, the third letter of characteristic access commands is W. Before addressing the characteristics, it is useful to know the accessible characteristics. The list commands group provides two commands, LC and LS, to list the client services and the server services, respectively.