Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
The detected tone bandwidth is set in accordance with the following table:
BANDWIDTH
Will Decode Will Not Decode
Bit 3
Bit 2
Bit 1
Bit 0
Recommended for CTCSS
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
±1.1%
±1.3%
±1.6%
±1.8%
±2.0%
±2.2%
±2.5%
±2.7%
±2.4%
±2.7%
±2.9%
±3.2%
±3.5%
±3.7%
±4.0%
±4.2%
$C8 (B2.5)
TX SUB-AUDIO LEVEL
Bit:
15
0
14
1
13
0
12
0
11
0
10
9
8
7
6
5
4
3
2
1
0
0
Sub-Audio Level (range 0 to 1023)
The ‘Sub-Audio Level’ bits 15 (MSB) to 8 (LSB) set the transmitted CTCSS or DCS sub-audio signal level (p-p)
with a resolution of VDD(A)/8192 per LSB (0.61mV per LSB at VDD(A)=5V, giving a range 0 to 624.4mV).
$C8 (B2.6 to B2.36, even)
RX CTCSS TONE
Bit:
15
0
14
1
13
0
12
0
11
10
9
8
7
6
5
4
4
3
2
1
0
0
Frequency Code
N (defined below)
R (defined below)
$C8 (B2.7 to B2.37, odd) RX CTCSS POLE COEFF
Bit:
15
0
14
1
13
12
11
10
9
8
7
6
5
3
2
1
Pole Coefficient
The ‘RX CTCSS TONE’ and ‘RX CTCSS POLE COEFF’ data are used to program the frequencies of up to 16
tones in the sub-audio band, that will be decoded by the receiver.
Each tone is identified by the ‘Tone Address’ address, which is determined by the order in which the tones are
programmed. ‘Tone Addresses’ range from 0 for the first tone to be programmed, through to 15 for the
sixteenth tone to be programmed.
The ‘Frequency Code’ bits (bits 11 to 0) of ‘RX CTCSS TONE’ contain the data representing the tone frequency
according to the formula below. If a tone is not required these 12 bits should be set to zero.
Sub-audio CTCSS tone formula:
N = (integer) (0.236 ´ frequency)
R = (0.236 ´ frequency - N) ´ 1500/frequency
The remaining 14 bits of ‘RX CTCSS POLE COEFF’ contain the data representing the pole coefficient according
to the formula below. For every programmed tone frequency, the corresponding pole coefficient must be
programmed at the same tone address. If a tone is not required these 14 bits should be set to zero.
Pole Coefficient = 16383 ´ Tan(0.0020944 ´ frequency)
[the value in brackets is in radians]
The ‘Tone Address’ (0 through to 15) is used as the code to indicate which tone has been decoded. This code
appears in the ‘RX Tone’ field of the ‘STATUS’ register.
ã 2001 Consumer Microcircuits Limited
64
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
