PTT ID:
     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 | DTMF system index+1, 0=none   | TX mode                       | ID mode                       | Start ID index+1, 0=none      |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
04 | End ID index+1, 0=none        | Unused, set to 0x00                                                                           |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Where:
  - TX mode: 0=None, 1=Pre, 2=Post, 3=Both
  - ID mode: 0=Forbidden, 1=Each, 2=Once
