Hello,
Hope you are doing well.
The UUID is a 128-bit value. To reduce the overhead associated with storing and transmitting 128‑bit UUIDs, the Bluetooth SIG has pre‑allocated a range of UUIDs for frequently used, registered purposes. These pre‑allocated UUIDs have 16‑bit aliases, commonly referred to as 16‑bit UUIDs. Although they are represented as 16‑bit values, each actually represents a 128-bit UUID value.
A list of Bluetooth SIG‑defined 16‑bit UUIDs can be found on the Assigned Numbers documentation of the Bluetooth Technology website. If you need a custom service intended for broader or official use, it is also possible to request and purchase an official 16‑bit UUID as a Bluetooth SIG member.
When defining a GATT database, the GATT_DB API provides several macros for declaring services. For 16‑bit UUIDs, the following macro is used: PRIMARY_SERVICE(name, uuid16). Both the UUID16 and PRIMARY_SERVICE macros support the Bluetooth SIG‑defined 2‑byte UUIDs. These 16‑bit UUID constants for GATT declarations are provided in the ble_sig_defines.h header file.
For more information on GATT services see Creating GATT database — MCUXpresso SDK Documentation
If you are looking is to implement a custom service using the wireless_uart SDK example, the recommended approach is to first define a 128‑bit UUID. In that case, you should use the UUID128 and PRIMARY_SERVICE_UUID128 macros instead. This example implementation might be helpful: KW38 Custom Profile.
Best regards,
Ana Sofia.
