CS4235 Datasheet, PDF (74/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
When APSEL is externally tied to SGND, the
Address Port is moved to one of two locations,
selected by a strapping option on the SCL pin. If
SCL is sampled high (default), then the Address
Port is moved to 0x308. If SCL is strapped low
with an external 10 kΩ resistor to SGND, the
Address Port is moved to 0x388.
If the Address Port is moved (APSEL = 0) then
the device is no longer PnP compliant; however,
it will still respond to all the standard PnP com-
mands using the new Address Port. In addition,
the new Address Port supports the traditional
Crystal Key or the new Crystal Key 2.
Multiplexed Pin Configuration
On the high to low transition of the RESDRV
pin, the part samples the state of the MCLK and
SDOUT which have internal 100 kΩ pullups to
+5 V.
The state of MCLK at the time RESDRV is
brought low determines the function of the
CDROM interface pins. If MCLK is sampled
high, then CDCS, CDACK, CDINT, CDRQ are
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 18 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 18. Line Inputs
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DS252PP2