Hello Gzz,
The difference would be that the 0x28 value is for an ACK after the data has been transmitted and the 0x30 is for a NACK or no acknowledgement after the data has been transmitted by the master.
You can see how it is used in the hal_i2c.c in the HalI2CWrite() function of BLE v1.3. They are defined as:
mstDataAckW = 0x28,
mstDataNackW = 0x30,
Thanks,
