CMX138 CML Microcircuits, CMX138 Datasheet - Page 30

• Manufacturer Part Number: CMX138
• Description: Audio Scrambler and Sub-Audio Signalling Processor
• Manufacturer: CML Microcircuits

Audio Scrambler and Sub-Audio Signalling Processor
7.6.2
The In-band tone to be generated is defined in the TX TONE register ($C3). The tone level is set in the
Programming register (P1.0). The In-band tone must be transmitted without other signals in the audio
band, so the host µC must disable the audio path prior to initiating transmission of an In-band tone and
restore it after the In-band tone transmission is complete.
7.7
The input to the Auxiliary ADC is routed through an inverting op-amp from the AuxADC input pin under
control of the AuxADC and Tx MOD mode register, $A7. Conversions will be performed as long as the
input source is selected; to stop the ADC, the input source should be set to “none”. Register $C0, b6
(BIAS) must be enabled for Auxiliary ADC operation.
Averaging can be applied to the ADC readings by selecting the relevant bits in the Signal Routing register,
$A7, the length of the averaging is determined by the value in the Programming register (P3.0), and
defaults to a value of 0. This is a rolling average system such that a proportion of the current data will be
added to the last average value. The proportion is determined by the value of the average counter in
P3.0, as follows:
For an average value of:
The maximum useful value of this field is 8. For a step input signal, this provides an exponential-style
response in the output data. Since the initial value for averaging will depend on previously sampled data,
it will require a number of samples to be taken before the value becomes representative of the true
average.
High and Low thresholds may be independently applied to the ADC channel (the comparison is applied
after averaging, if this is enabled) and b8 of the IRQ Status register ($C6) will be set (and an IRQ
generated, if enabled) whenever the signal crosses above the High threshold or below the Low threshold
(except in the case where the high threshold has been set below the low threshold). The threshold status
can be determined from b15 and b14 of the AuxADC data register ($A9). The thresholds are programmed
via the AuxADC Threshold register ($B5).Auxiliary ADC data is read back in the AuxADC Data register
($A9) and includes the threshold status as well as the actual conversion data (subject to averaging, if
enabled). Note that the thresholds are inverted due to the op-amp on the AuxADC input pin.
© 2008 CML Microsystems Plc
b15
0
1
x
0 = 50% of the current value will be added to 50% of the last average value,
1 = 25% of the current value will be added to 75% of the last average value
2 = 12.5% etc.
Auxiliary ADC Operation
Transmitting In-band Tone
b14
0
0
1
b13
0
0
1
b12
0
0
1
b11
0
0
1
Table 5 In-band Tone
Rx Mode $CC
No tone
Tone Detected
Unrecognised Tone
Page 30
Tx Mode $C3
No tone
Transmit In-band Tone
reserved
D/138_FI1.0/5
CMX138