The sel call encoder module is used to transmit selective calling tone
sequences. To send a sel call sequence, send a DTMF command where the first
two digits represent the sel call standard to use and where the rest of the
digits are the actual sequence of digits to send.

Available standards are:

0 1, ZVEI1.
0 2, ZVEI2.
0 3, ZVEI3.
0 4, P ZVEI.
0 5, D ZVEI.
0 6, E E Eigh.
0 7, C C I R 1.
0 8, C C I R 2.
0 9, V D E W.
10, C C I T T.
11, NATEL.
12, E I Eigh.
13, EURO.
14, MODAT.
15, P D ZVEI.
16, P C C I R.
17, AUTO Eigh.

