CS4237B Datasheet, PDF (90/114 Pages) Cirrus Logic – CrystalClear Advanced Audio System with 3D Sound

CS4237B
If VCEN is zero, then if ACDbase is ever pro-
grammed to a non-zero value, this pin converts
to the ACDCS pin and keeps this function until
the part is reset (or VCEN is set to one). If
ACDbase is never programmed non-zero, then
the state of XIOW at the time RESDRV is
brought low determines whether the pin is
XCTL1 or SINT. If XIOW is sampled low (ex-
ternal pulldown) then XCTL1/SINT/
ACDCS/DOWN functions as an input for the
synthesizer interrupt. If XIOW is sampled high
(pin left unconnected) then XCTL1/SINT/
ACDCS/DOWN becomes an output for XCTL1.
This part contains another multiplexed pin,
SCS/UP. This pin provides the FM synthesizer
chip select or the hardware volume control "vol-
ume up" feature. Since an internal FM
synthesizer exists, this pin would normally be
used for the volume control feature. Setting
VCEN forces this pin to the UP volume control
function. When VCEN is clear, this pin is the
SCS chip select function.
ANALOG HARDWARE DESCRIPTION
The analog hardware consist of an MPC
Level 2-compatible mixer (four stereo mix
sources), three line-level stereo inputs, a stereo
microphone input, a mono input, a mono output,
and a stereo line output. This section describes
the analog hardware needed to interface with
these pins.
Line-Level Inputs Plus MPC Mixer
The analog inputs consist of four stereo analog
inputs, and one mono input. As shown in Fig-
ure 4, the input to the ADCs comes from the
Input Mixer that selects any combination of the
following: LINE, AUX1, AUX2, MIC, the DAC
output, and the output from the analog output
mixer. Unused analog inputs should be con-
nected together and then connected through a
capacitor to analog ground.
The analog input interface is designed to accom-
modate four stereo inputs and one mono input.
Four of these sources are mixed to the ADC.
These inputs are: a stereo line-level input
(LINE), a stereo microphone input (MIC), a ste-
reo CD-ROM input (AUX2), and a stereo
auxiliary line-level input (AUX1). The LINE
and AUX1 inputs have two paths to the Input
Mixer. One path is direct with no volume con-
trol. The other path goes through an inverting
amplifier, which enables volume control. Care
should be taken to select only one of these dual
paths, because the inverting path will cancel the
signal of the non-inverting path at the Input
Mixer. The LINE, MIC, AUX1, and AUX2 in-
puts have paths after their volume controls, to
the output mixer. The output mixer has the addi-
tional input of a mono input channel. All audio
inputs should be capacitively coupled.
To obtain Sound Blaster mixer compatibility, the
mapping of external devices to analog inputs is
important. An external FM or Wavetable synthe-
sizer analog output must be connected to the
LINE input. The internal FM’s volume control,
when enabled, maps to the LINE analog mixer
registers. The CDROM analog outputs must be
connected to the AUX2 inputs, and the external
Line Inputs must be connected to the AUX1 ana-
log inputs.
Since some analog inputs can be as large as
2 V_RMS, the circuit shown in Figure 26 can be
used to attenuate the analog input to 1 V_RMS
which is the maximum voltage allowed for the
line-level inputs.
6.8 kΩ
6.8 kΩ
6.8 kΩ
1.0 µF
R
1.0 µF
L
6.8 kΩ
Figure 26. Line Inputs
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