Service Manual
17
external MIC is connected to the MIC_HED of the codec as a unit-directional input. Both MICs are
controlled by Q232. When the internal MIC is active, EXT_MIC_EN is at low level, bias voltage of
external MIC is disconnected, and the ADC in U231 senses voltage at the MICIN_HND. When the
external MIC is active, EXT_MIC_EN is at high level, Q232 is turned on, bias voltage is connected, and
the ADC in U231 senses only audio data at MICIN_HED.
Audio signals input from the MMP interface or the accessory jack, are fed to the codec (gain of codec is
programmable via the CPS) and then are converted by the ADC into 16-bit PCM digital audio, which will
be fed to U302 via the SSI interface.
When the radio is set to operate in loudspeaker mode, audio signal is generated by the internal MIC, and
then feeds to U231, and finally is output via SPK2. The output audio signal is amplified, and then is
output as the two paths of audio PUB_ADDRESS1 and PUB_ADDRESS2.
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