Cirrus Logic CS4205 - Manual (Page 14)

CS4205
14 DS489PP4
2.2 Control Registers
The CS4205 contains a set of AC ’97 compliant
control registers, and a set of Cirrus Logic defined
control registers. These registers control the basic
functions and features of the CS4205. Read access-
es of the control registers by the AC ’97 controller
are accomplished with the requested register index
in Slot 1 of a SDATA_OUT frame. The following
SDATA_IN frame will contain the read data in Slot
2. Write operations are similar, with the register in-
dex in Slot 1 and the write data in Slot 2 of a
SDATA_OUT frame. The function of each input
and output frame is detailed in Section 4, AC-Link
Frame Definition. Individual register descriptions
are found in Section 5, Register Interface.
2.3 Sample Rate Converters
The sample rate converters (SRC) provide high ac-
curacy digital filters supporting sample frequencies
other than 48 kHz to be captured from the CS4205
or played from the controller. AC ’97 requires sup-
port for two audio rates (44.1 and 48 kHz) and four
modem rates (8, 9.6, 13.714, and 16 kHz). In addi-
tion, the Intel
® I/O Controller Hub (ICHx) specifi-
cation [9] requires support for five more audio rates
(8, 11.025, 16, 22.05, and 32 kHz) and specifies
two optional modem rates (24, 48kHz). The
CS4205 supports all these rates, as shown in
Table 12 on page 38.
2.4 Mixers
The CS4205 input and output mixers are illustrated
in Figure 8. The stereo input mixer sums together
the analog inputs to the CS4205 according to the
settings in the volume control registers. The stereo
output mixer sums the output of the stereo input
mixer with the PC_BEEP and PHONE signals. The
stereo output mix is then sent to the LINE_OUT
pins of the CS4205. The mono output mixer gener-
ates a monophonic sum of the left and right audio
channels from the stereo input mixer. The mono
output mix is then sent to the MONO_OUT pin on
the CS4205.
2.5 Input Mux
The input multiplexer controls which analog input
is sent to the ADCs. The output of the input mux is
converted to stereo 18-bit digital PCM data and
transmitted to the controller by means of the
AC-link SDATA_IN signal.
2.6 Volume Control
The CS4205 volume registers control analog input
levels to the input mixer and analog output levels,
including the master volume level. The PC_BEEP
volume control uses 3 dB steps with a range of 0 dB
to -45 dB attenuation. All other analog volume con-
trols use 1.5 dB steps. The analog inputs have a
mixing range of +12 dB signal gain to -34.5 dB sig-
nal attenuation. The analog output volume controls
have a range of 0 dB to -46.5 dB attenuation for
LINE_OUT and MONO_OUT.
2.7 Dedicated Mic Record Path
The CS4205 includes a dedicated microphone
ADC that supports advanced functions such as
speech recognition and internet telephony. The
dedicated ADC allows recording of a microphone
input independent of the input mux settings. This
enables simultaneous capture of microphone and
independent stereo sources.