CS4239 Datasheet, PDF (76/98 Pages) Cirrus Logic – CrystalClear™ Portable ISA Audio System

CS4239
CrystalClear^TM Portable ISA Audio System
used to input SA12, SA13, SA14, SA15 respec-
tively. If MCLK is sampled low (external
pulldown) then CDCS, CDACK, CDINT, CDRQ
become the standard CDROM interface pins.
The XCTL1/ACDCS/DOWN pin state is first
determined by VCEN. If VCEN is set this pin is
forced to the DOWN volume control pin. If
VCEN is zero, then a strapping option on
SDOUT determines the pin function. If SDOUT
is high (default) on powerup, the pin is forced to
the XCTL1 general purpose output that tracks
the bit by the same name in I10 in the WSS
space. If SDOUT is externally pulled low
through a 10 kΩ resistor, then the pin is forced
to the alternate CDROM chip select function,
ACDCS.
ANALOG HARDWARE DESCRIPTION
The analog hardware consist of an MPC
Level 3-compatible mixer. This section describes
the analog hardware needed to interface with
these pins.
Line-Level Inputs
The analog inputs consist of three 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: AUX1, AUX2, MIC, DAC1, DAC2,
and the output from the analog output mixer.
Unused analog inputs should be connected to-
gether and then connected through a capacitor to
analog ground.
The analog input interface is designed to accom-
modate two stereo inputs and two mono inputs.
Three of these sources are mixed to the ADC.
These inputs are: a mono microphone input
(MIC), a stereo CD-ROM input (AUX2), and a
stereo auxiliary line-level input (AUX1). The
MIC, AUX1, and AUX2 inputs have paths after
their volume controls, to the output mixer. The
output mixer has the additional input of a mono
input channel. All audio inputs should be capaci-
tively coupled.
Since some analog inputs can be as large as
2 V_RMS, the circuit shown in Figure 19 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 19. Line Inputs
The AUX2 line-level inputs have an extra pin,
CMAUX2, which provides a pseudo-differential
input for both LAUX2 and RAUX2. This pin
takes the common-mode noise out of the AUX2
inputs when connected to the ground coming
from the AUX2 analog source. Connecting the
AUX2 pins as shown in Figure 20 provides extra
noise attenuation coming from the CDROM
drive, thereby producing a higher quality signal.
Since the better the resistors match, the better the
common-mode attenuation, one percent resistors
are recommended. If CMAUX2 is not used, it
should be connected through an AC cap to ana-
log ground.
(All resistors 1%)
6.8 kΩ
3.4 kΩ
1.0 µF
2.0 µF
RAUX2
CMAUX2
LAUX2
6.8 kΩ
6.8 kΩ
1.0 µF
3.4 kΩ ^{6.8 kΩ}
Figure 20. Differential CDROM In
76
DS253PP2