m4a5a_v320_eng (14.02.2013)
- 20 -
Kompetent für Elektroniksysteme
m4a5a_v320_eng (14.02.2013)
- 21 -
Kompetent für Elektroniksysteme
Major 4a can be used in mixed networks, where FFSK and common tone sequence signalling
(see Transmitting 5-Tone Sequences) are to be used simultaneously. Therefor, a FFSK-decoder/
encoder is active in addition to the tone-decoder/encoder.
Composition of a Telegram
The call telegram starts with an unmodulated carrier that has to be present at the receiver for
at least 25 ms. This is followed by a 16-bit digital sequence and the block synchronization. For
block synchronization a 15-bit barker word with a preceding 1 is used. The following selective call
consists of 8 digits:
1
st
digit: code of the mode of operation (CMO) (invariable)
2
nd
digit: status (invariable)
3
rd
digit: hash key identification (invariable)
4
th
+5
th
digit: producer identification (variable)
6
th
-8
th
digit: call (variable)
Code of the Mode of Operation (CMO)
The CMO distiguishes the different types of telegrams. The following types are supported by the
Major:
Nr.
Meaning
Major
0
available (free)
(x)
1 Q call to car
x
2 Q call to control center
x
3
ID code
x
4
acknowledgement
x
5
additional telegram
6 Q cutting call
7
reserve
8 Q priority call
9 Q status request
A
reserve
B
reserve
C
reserve
D
available (free)
E
available (free)
F
emergency call
x
CMOs marked with a Q require an acknowledgement. The CMO is programmed together with the
PTT button at digit 5 (usually with ‘1’ => call to car, standard: call button, short press; see Table of
Registers, register 172).
The CMO for call decoding is programmed in register 091 (2
nd
digit, usually programmed with ‘2’ =>
call to control center).
FFSK mode