Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
Transmitting Signals On Analogue Channels
Modulator Output Routing:
The sub-audio component can be combined with the voice band signal and this composite signal routed to both
MOD_1 and MOD_2 outputs, or the sub-audio and voice band signal can be output separately (sub-audio to
MOD_2 and voice band to MOD_1), in accordance with the settings of the ‘ANALOGUE OUTPUT PATH
CONFIGURATION’ register ($B1).
CTCSS Tone:
The sub-audio CTCSS tone generated is defined by the ‘TX CTCSS TONE’ word (B2.1) in the ‘PROGRAMMING
REGISTER’’ ($C8). Table 10 lists the commonly used CTCSS tones and the corresponding values for
programming the ‘TX CTCSS TONE’ word. This does not preclude other tones being programmed.
Table 10 CTCSS TX Tone Programming
Freq.
(Hz)
67.0
69.3
Tone Code
(hex)
C224
Freq.
(Hz)
Tone Code
(hex)
C3AC
C3CD
C3EF
C412
Freq.
(Hz)
Tone Code
(hex)
C5F5
C613
C62B
C64A
C662
C683
C69B
C6BE
C6FA
C738
C754
C779
C7BC
C802
C821
114.8
118.8
123.0
127.3
131.8
136.5
141.3
146.2
151.4
156.7
159.8
162.2
167.9
173.8
179.9
183.5
186.2
189.9
192.8
196.6
199.5
203.5
206.5
210.7
218.1
225.7
229.1
233.6
241.8
250.3
254.1
C237
C24C
C261
71.9
74.4
77.0
79.7
82.5
85.4
88.5
91.5
94.8
97.4
100.0
103.5
107.2
110.9
C276
C437
C45E
C485
C4AD
C4D8
C503
C51D
C530
C55F
C58F
C5C1
C5DF
C28C
C2A3
C2BB
C2D4
C2ED
C308
C31D
C333
C34F
C36E
C38C
134.4
C44D
(134.4Hz is the DCS end identification tone.)
DCS Code:
A 23 or 24-bit sub-audio DCS Code can be generated, as defined by the ‘DCS Code’ words (B2.2, B2.3) of the
‘PROGRAMMING REGISTER’ ($C8); the same DCS Code register is used for Rx detection and transmission.
The DCS Code is NRZ encoded at 134.4±0.4bits/s, low pass filtered and added to the digitised voice signal, prior
to passing the signal to the interpolation and Delta-Sigma DAC and modulator output stages. The valid 23-bit
DCS codes and the corresponding settings for the DCS Code Register are shown in Table 5. This does not
preclude other codes being programmed. The least significant bit of the DCS code is transmitted first and the
most significant bit is transmitted last. The CMX880 is able to encode and transmit either of the two DCS
modulation modes defined by TIA/EIA-603 and described in Table 4.
To signal the end of the DCS transmission, the mC should set the CTCSS Tx tone register to 134.4Hz, disable
DCS code transmit and turn on the CTCSS tone transmit for 150ms to 200ms. The CMX880 has specific
capability to ensure a smooth transmission from DCS code to CTCSS tone so that the ‘turn off’ tone is issued in
phase with the last DCS code bit transmitted.
ã 2001 Consumer Microcircuits Limited
30
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
