DTMF System:
     7   6   5   4   3   2   1   0   7   6   5   4   3   2   1   0   7   6   5   4   3   2   1   0   7   6   5   4   3   2   1   0
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
00 | Side tone enable              | Unused, set to 0x00           | Pre time in ms, uint16, little endian                         |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
04 | Code duration in ms, uint16, little endian                    | Code Intervall in ms, uint16, little endian                   |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
08 | Reset time in 0.1s, uint16, little endian                     | Unused, set to 0x00                                           |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
