CMX138 CML Microcircuits, CMX138 Datasheet - Page 24

• Manufacturer Part Number: CMX138
• Description: Audio Scrambler and Sub-Audio Signalling Processor
• Manufacturer: CML Microcircuits

Audio Scrambler and Sub-Audio Signalling Processor
7.5
Sub-audio signalling is available in the audio band below 260Hz. When sub-audio signalling is enabled,
the 300Hz HPF in the audio section should also be enabled to remove the sub-audio signalling from the
audio signal (in both Tx and Rx). Both CTCSS tones and DCS codes are supported, as well as a special
Tone Clone™ mode which will report back any received CTCSS tone rather than look for a specific tone.
There are 51 CTCSS tones defined in the CMX138 and there is provision for a user-specified tone. Tone
phase adjustment (180 or 120 degrees) to implement “Reverse Tone Burst” for squelch tail elimination
can be accomplished by setting b9, b8 of the Audio Control register, $C2.
The DCS coder / decoder supports both 23- and 24-bit modes with both true and inverse modulation
formats and the 134Hz end of transmission burst.
The CTCSS tone and DCS code values for both Rx and Tx operation are specified in the Audio Control
register ($C2), in the lowest 8 bits (shown in decimal):
These are detailed in Table 2. The inverted DCS codes are shown in the grey section of the table.
The CTCSS and DCS functions are enabled by the relevant bits in the Mode Control register, $C1, so that
the host can turn the functionality on or off without having to re-program the values in the Audio Control
register, $C2.
See:
© 2008 CML Microsystems Plc
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Sub-audio Signalling
0
1 to 83
84
101 to 183
184
200
201 to 254
255
Analogue Input Gain - $B0 write
Mode Control – $C1 write
Audio Control – $C2 write
No tone
DCS code 1 to 83
User-defined DCS code
Inverted DCS code 1 to 83
Inverted user-defined DCS code
CTCSS Tone Clone™ mode
CTCSS tones 1 to 51, User, XTCSS and DCSoff tones
Invalid tone
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D/138_FI1.0/5
CMX138