FRS Signalling Processor
CMX882
1.6.20.2 PROGRAMMING REGISTER Block 1 – XTCSS and In-band tone Setup:
$C8 (P1.0)
Voice band tones Tx Level
Bit:
15
1
14
1
13
0
12
1
11
10
9
8
7
6
5
4
3
2
1
0
P1.0
Voice band tones Tx level
Emph
Bits 11 (MSB) to 1 (LSB) set the transmitted In-band tone, Audio Tone and MSK signal level (pk-pk) with
a resolution of VDD(A)/2048 per LSB (1.465mV per LSB at VDD(A)=3V). Valid range for this value is 0 to
1536.
Bit 0 controls Rx In-band tone de-emphasis. When set to '0' the signal going to the In-band tone detector
is not de-emphasised. When voice processing is enabled in the Mode register, de/pre-emphasis is
enabled in the Audio & Device Address register and this bit (b0) is set to '1', signals going to the In-band
tone detector are de-emphasised in accordance with Figure 6.
$C8 (P1.1)
In-band tone Detect Bandwidth and Audio Band Detect Threshold
Bit:
15
0
14
1
13
0
12
1
11
XTCSS
tone length
10
9
8
7
6
5
4
3
2
1
0
In-band tone detect
P1.1
Audio band detect threshold
bandwidth
XTCSS tone length (bits 11 to 10) set the transmit tone length for each of the 4 tones in a XTCSS
sequence. In receive these bits define the minimum silent prefix and suffix qualification periods for
successful reception, also the maximum receive tone length is double the time set (e.g. for 60ms setting
each received tone must be less than 120ms in length for successful XTCSS decoding). '00' = 40ms,
'01' = 60ms, '10' = 80ms and '11' = 100ms.
The ‘detect threshold’ bits (bits 9 to 4) set the minimum In-band tone and/or MSK signal level that will be
detected. The levels are set according to the formula:
Minimum Level = Detect Threshold × 3.63mV rms at VDD(A) = 3V
The In-band tone detected bandwidth is set in accordance with the following table:
BANDWIDTH
Bit 3
Bit 2
Bit 1
Bit 0
Will Decode
±1.1%
Will Not Decode
±2.4%
1
1
1
1
0
0
0
0
0
0
1
1
0
1
0
1
±1.3%
±2.7%
Recommended for EEA ⇒
±1.6%
±2.9%
±1.8%
±3.2%
$C8 (P1.2-5) Programmable In-band Tones
Bit:
15
0
14
1
13
0
12
1
11
0
10
9
8
7
6
5
4
3
2
1
0
P1.2-5
Programmable In-band Tone
N (see below)
R (see below)
These words set the programmable In-band tones used in transmit and receive. The frequency is set in
bits 10-0 for each word according to the formula:
N = Integer part of (0.042666 x frequency)
R = (0.042666 x frequency - N) x 6000 / frequency (round to nearest integer)
Example: For 1010Hz, N = 43, R = 1. The programmed tones must only be set to frequencies from
400Hz to 3000Hz.
2004 CML Microsystems Plc
53
D/882/7
CMLMICRO [ CML MICROCIRCUITS ]
