USB Audio 2.0 Reference Design, XS1-L1 Edition Hardware Manual (1.0)
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These master clock frequencies were chosen due to the easy availability of crystals
at these frequencies.
The reset pin on the CODEC is mapped to bit 1 of port 32A on the processor.
4.1
Audio IO
Two 3.5mm Tip Ring Sleeve (TRS) audio jacks are provided for stereo audio input
and output. The layout of the audio jacks is displayed below:
OUT
IN
A simple passive ac-coupling and low pass filter circuit is used on input and output.
The circuit is configured so that the audio output will produce approximately 1V
RMS
(0dBV) for a digital full scale signal. Due to the output coupling capacitors, the
output impedance falls with frequency and is approximately 1k
Ω
@ 35Hz falling to
576
Ω
@ 1kHz.
The input circuit contains an attenuator such that a 2V
RMS
(+6dBV) signal will produce
a full scale digital output. The input impedance is approximately 8k
Ω
.
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