Audio Scrambler and Sub-Audio Signalling Processor
CMX138A
0000
0001
0010
0011
0100
0101
- - - -
1111
InputAGC off
InputAGC on, release time = 64ms
InputAGC on, release time = 128ms
InputAGC on, release time = 196ms
InputAGC on, release time = 256ms
InputAGC on, release time = 320ms
- - - - - - - - - - - - - - - - - - - - - - - - - -
InputAGC on, release time = 960ms
b7-0 set the order of the Audio Filter processing. This feature can be used to optimise the signal to noise
performance of particular radio hardware designs. Each filter/process block can be specified in any order.
Each two-bit field specifies the order in which the process will be executed in Tx mode, therefore it is
imperative that each set of bit fields be different. The reverse sequence is used in Rx mode. The voice
filter and soft limiter will always be implemented as the final block in the Tx sequence.
The default settings are:
o
o
o
o
Pre-emphasis: 01 (pre-emphasis in position 1)
Compandor:
Scramble:
00 (Compandor in position 0)
10 (Scrambler in position 2)
11 (HPF in position 3)
300Hz HPF:
which will implement the line-up as shown in Figure 16 and Figure 17.
Compress
(optional)
Pre-emph
(optional)
Scrambler
(optional)
Voice LPF &
Soft Limiter
Audio in
300Hz Filter
+
CTCSS
Figure 16 Default Tx Audio Filter Line-up
De-scrambler
(optional)
De-emph
(optional)
Expander
(optional)
Discrim
Voice LPF
300Hz Filter
Audio
Figure 17 Default Rx Audio Filter Line-up
$C8 (P4.10)
Reserved
Bit:
15
14
13
12
11
10
9
8
7
6
5
4
4
3
3
2
2
1
1
0
0
P4.10
0
0
reserved – set to $0608
Reserved – set to $0608
$C8 (P4.11) Input AGC Threshold Level
Bit:
15
0
14
0
13
12
11
10
9
8
7
6
5
P4.11
Threshold Level
This unsigned hex number sets the threshold level for the Input AGC function.
Default is $0FFF = VBIAS ± AVDD/4.
© 2010 CML Microsystems Plc
Page 59
D/138A/2
CMLMICRO [ CML MICROCIRCUITS ]
