As far as I'm concerned, a nibble is a 4-bit group. For example, the byte 0xA1 (0b10100001 ) is split into two nibbles, 0xA and 0x1 (0b1010 and 0b0001 respectively), and the most significant bit of that byte is 0x1, (I'm using the little-endian format). The sequence 0xA1B2C3 is split into 6 nibbles, 0xA, 0x1, 0xB, 0x2, 0xC and 0x3. Assuming a little-endian format, the most significante byte is 0xA1, and the most significante bit of all the 24-bit sequence is 0b1. The sane logic applies to any other byte sequence, such as the one you provided.