CS4297 datasheet(29/46 Pages) CIRRUS

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DS242F5

CS4297

CrystalClear™ SoundFusion™ Audio Codec ’97

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:

Table 9. Powerdown GPR Bit Functions

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

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.

PR Bit

Function

PR0

Main ADC’s and Input Mux Powerdown

PR1

Main DAC’s Powerdown

PR2

Analog Mixer Powerdown (Vref on)

PR3

Analog Mixer Powerdown (Vref off)

PR4

AC-Link Powerdown (BIT_CLK off)

PR5

Internal Clock Disable

PR6

Alternate Line Out Buffer Powerdown

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