Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
$C9 C4FM FS CROSS-CORRELATION PEAK: 16-bit read only
Bit:
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
FS Cross-Correlation Peak
The value in this register provides quality information on the C4FM Frame Sync pattern recognition. Figure 21
shows how the FS cross-correlation peak value is affected by the signal to noise ratio.
72
71
70
69
68
67
0
5
10
15
20
25
SNR (dB)
Figure 21 SNR vs Nominal C4FM Frame Sync Cross-Correlation Peak
This curve assumes no FS pattern level mismatches. If the FS threshold level is programmed sufficiently low to
accommodate low signal to noise, there is a risk that a false FS pattern may be detected under less noisy signal
conditions. To minimise the risk of false FS detection, the user should also programme the FS tolerance control
of the RX Mode control register accordingly, or validate the FS detection by reading the FS tolerance status of
the ‘STATUS’ register.
$C1 TRANSMIT MODE CONTROL: 16-bit write-only
15
14
13
12
11
10
9
8
Bit:
DCS
Inverse
Voice EN
CTCSS TX
DCS TX
Selcall TX
DTMF TX
FFSK/MSK
TX
2400 Baud
7
6
5
4
3
2
1
0
Bit:
CQPSK TX
C4FM TX
Voice Filter Mode Select
Enable
Enable
TX EN
Ramp down
Ramp up
The Sub-Audio select bits determine what if any sub-audio is to be added to the signal before it is transmitted.
Bit 13
Bit 12
0
0
1
1
0
1
0
1
No Sub-Audio Transmitted
DCS Code Transmit
CTCSS Tone Transmit
Reserved – do not use.
The In-Band select bits determine what if any in band tones are to be added to the signal before it is transmitted.
The voice signal must be disabled, by clearing ‘Voice Enable’ bit 14 to 0, before transmitting Selcall, DTMF or
FFSK tones.
ã 2001 Consumer Microcircuits Limited
52
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
