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Chapter 5 Input/Output Interfaces
5-30 Compaq Deskpro EXS and Workstation 300 Personal Computers
Featuring the Intel Pentium 4 Processor
First Edition – December 2000
5.8.4 AUDIO CODEC
The Cirrus Logic CS4297A audio codec provides pulse code modulation (PCM) coding and
decoding of audio information as well as the selection and/or mixing of analog channels. As shown
in Figure 5-11, analog audio from a microphone, tape, or CD can be selected and, if to be recorded
(saved) onto a disk drive, routed through an analog-to-digital converter (ADC). The resulting left
and right PCM record data are muxed into a time-division-multiplexed (TDM) data stream (SD IN
signal) that is routed to the audio controller. Playback (PB) audio takes the reverse path from the
audio controller to the audio codec as SD OUT data and is decoded and processed by the digital-
to-analog converter (DAC). The codec supports simultaneous record and playback of stereo (left
and right) audio. The Sample Rate Generator may be set for sampling frequencies up to 48 KHz.
Analog audio may then be routed through 3D stereo enhancement processor or bypassed to the
output selector (SEL). The integrated analog mixer provides the computer control-console
functionality handling multiple audio inputs.
Figure 5-11. CS4297A Audio Codec Functional Block Diagram
All inputs and outputs are two-channel stereo except for the microphone input, which is inputted as
a single-channel but mixed internally onto both left and right channels. The microphone input is
the default active input. All block functions are controlled through index-addressed registers of the
codec.
Output
Amps
Sample
Rate
Gen.
Audio
Format
AC97
Link
I/F
Rec.
Input
Select
Mic In
Line In
CD In
Audio
Controller
Rec
Gain/
Mute
3D
Proc.
Audio
S
E
L
ADC
Rec
Data
PB
Data
AC97
Link Bus
Master
Gain/
Mute
Aux In
S
E
L
Σ/
Mixer
Gain/Mute
Gain/Mute
Gain/Mute
Gain/Mute
Gain/Mute
DAC