Marine VHF Audio and Signalling Processor
CMX885
0
8.1.27 Audio Tone – $CD write
15
0
0
0
0
1
1
1
1
1
1
1
14
0
0
1
1
0
0
0
1
1
1
1
13
0
1
0
1
0
1
1
0
0
1
1
12
0
0
0
0
0
0
1
0
1
0
1
11
10
9
8
7
6
5
4
3
2
1
Audio Tone Frequency
Audio Tone Level
Rx Voice Level
Output1 Fine Gain (also see P4.2)
Output2 Fine Gain (also see P4.3)
Tx Voice Level Multiplier
reserved
MOD1 and MOD2 Fine Attenuation
reserved
reserved
reserved
All other values reserved
Bits 15-12 determine how the remaining bit fields will be interpreted:
00002:
When the appropriate bit of the Mode Control register $C1:b10 is set, an audio tone will be generated with
the frequency set by bits (11-0) of the Audio Tone register in accordance with the formula below. If bits
11-0 are programmed with 0, no tone (i.e. VBIAS) will be generated when the Audio Tone is enabled.
Frequency = Audio Tone (i.e. 1Hz per LSB)
The Audio Tone frequency should only be set to generate frequencies from 288Hz to 3000Hz.
The host should disable other audio band signalling and set the correct audio routing before generating
an audio tone and re-enable signalling and audio routing on completion of the audio tone. The timing of
intervals between these actions is controlled by the host µC.
This register may be written to whilst the audio tone is being generated, any change in frequency will take
place after the end of the C-BUS write to this register. This allows complex sequences (e.g. ring or alert
tunes) to be generated for the local speaker (Tx or Rx via the AUDIO pin) or transmitted signal (Tx via the
MOD1/MOD2 pins).
00102:
The Audio Tone Level may be attenuated by the value written to b11-0. The default value of $FFF is
equivalent to x1. Note that this adjustment will affect ALL signals generated by the In-Band signalling
block (DTMF, FSK, Audio Tone). This register operates in parallel with P1.0, but allows the level to be
adjusted “on-the-fly” without needing to drop back into Idle mode.
01002:
In Rx mode, the voice level may be attenuated by the value written to b11-0. The default value of $FFF is
equivalent to x1. Note that this adjustment will only affect signals in the voice processing path as enabled
by the Mode Control register $C1:b14. This allows the voice level to be adjusted “on-the-fly” and in
conjunction with the Audio Output attenuator $B0:b3 to b0, offers a “fine gain” volume control.
Approximate values for 0.2dB steps are shown in Table 5.
© 2010 CML Microsystems Plc
48
D/885/3
CMLMICRO [ CML MICROCIRCUITS ]
