Compaq 850 manual Audio Codec, Dac

Chapter 5 Input/Output Interfaces

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.

	Mic In
	Line In			Rec.	Rec
	CD In			Input	Gain/
				Select	Mute
	Aux In
		Gain/Mute
		Gain/Mute
	Σ /	Gain/Mute
	Mixer
		Gain/Mute
		Gain/Mute
	Audio Master	S	S
Output			E	3D
	Gain/	E	L
Amps				Proc.
	Mute	L

Audio

Format

Rec

ADC Data

Sample AC97

Rate Link

Gen. I/F

	PB
DAC	Data

AC97

Link Bus

Audio

Controller

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.

5-30Compaq Deskpro EXS and Workstation 300 Personal Computers Featuring the Intel Pentium 4 Processor

First Edition – December 2000