cs4297 Cirrus Logic, Inc., cs4297 Datasheet - Page 29

• Manufacturer Part Number: cs4297
• Description: Crystalclear Soundfusion Audio Codec 97 Logic
• Manufacturer: Cirrus Logic, Inc.

DS242F5
POWER MANAGEMENT
The AC’97 Specification defines a mixer register
called the Powerdown Control/Status register (in-
dex 26h) for controlling power management func-
tions within the CS4297. In the CS4297, 7 of these
bits (bits 14 - 8) have defined functions. In effect,
all portions of the Codec can be shut down individ-
ually and powered back up by a single Cold or
Warm Reset sequence.
The following table shows the mapping of the pow-
er control bits to the functions they manage:
When, for example, PR0 is ‘set’, the main ADCs
and the Input Mux are shut down and the ADC bit
(bit 0 in register 26h) is ‘cleared’ to indicate the
ADCs are no longer in a ready state. The same is
true for the DACs, the Analog Mixers, and the Ref-
erence Voltage (Vrefout). When the PR bit for one
of these portions of the Mixer is ‘cleared’, the Mix-
er section will begin a power-on process, and the
corresponding Powerdown Status bit will be ‘set’
when the hardware is in a ready state.
Bit PR4, which shuts down the AC-Link, causes
the AC-Link to turn off the BIT_CLK and drive
SDATA_IN to a ‘0’. It also ignores SYNC and
SDATA_OUT in their normal capacities. To re-
store operation to the part from this state, either a
Cold or a Warm Reset is required (see Cold AC’97
Reset and Warm AC’97 Reset). A Cold Reset will
restore all Mixer registers to their power-on default
values. A Warm Reset will not alter the values of
CS4297
CrystalClear™ SoundFusion™ Audio Codec ’97
PR Bit
PR0
PR1
PR2
PR3
PR4
PR5
PR6
Table 9. Powerdown GPR Bit Functions
Main ADC’s and Input Mux Powerdown
Main DAC’s Powerdown
Analog Mixer Powerdown (Vref on)
Analog Mixer Powerdown (Vref off)
AC-Link Powerdown (BIT_CLK off)
Internal Clock Disable
Alternate Line Out Buffer Powerdown
Function
any Mixer register (with the exception of ‘clearing’
the PR4 bit of register 26h).
Setting bit PR5 causes a global powerdown of the
Codec. In this state, all internal clocks of the
CS4297 are shut down. A Cold Reset is the only
way to restore operation to the CS4297 in the Glo-
bal Powerdown state.
One important note: The CS4297 does not auto-
matically mute any input or output when the pow-
erdown bits are ‘set’. It is left to the software driver
controlling the AC’97 device to manage muting the
input and output analog signals before putting the
part into any power management state.
ANALOG HARDWARE DESCRIPTION
The analog hardware consist of a four line-level
stereo inputs, two selectable mono microphone in-
puts, two mono inputs, a mono output, and dual, in-
dependent stereo line outputs. This section
describes the analog hardware needed to interface
with these pins.
Line-Level Inputs
The analog inputs consist of four stereo analog in-
puts and four mono inputs. As shown in Figure 1,
the input to the ADCs comes from the Input Mux
which selects one of the following: Phone (Mono),
Aux, Video, CD, Mic1 or Mic2 (Mono), Line, Ste-
reo Output Mix, or the Mono Output Mix (Mono).
Unused analog inputs should be connected together
and then connected through a capacitor to analog
ground or tied to the Vrefout line directly.
The analog input mixer is designed to accommo-
date five stereo inputs and one mono input. These
inputs are: a stereo line-level input (LINE), a mono
microphone input (MIC), a stereo CD-ROM input
(CD), a stereo auxiliary line-level input (AUX),
and the PCM output from the DACs. Each of the
stereo inputs has separate volume controls for each
channel and one mute control for each left/right
pair. The mono microphone input has one mute and
one volume control.
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