STAC9750 datasheet(33/73 Pages) IDT

33 / 73 page

STAC9750/9751

VALUE-LINE TWO-CHANNEL AC’97 CODECS

PC AUDIO

IDT™

STAC9750/9751

V 5.8 103106

VALUE-LINE TWO-CHANNEL AC’97 CODECS

6.1.

Analog Mixer Input

The mixer provides recording and playback of any audio sources or output mix of all sources. The

STAC9750/9751 supports the following input sources:

•

Any mono or stereo source

•

Mono or stereo mix of all sources

•

Two-channel input with mono output reference (microphone + stereo mix)

Note: All unused inputs should be tied together connected to ground through a capacitor (0.1

µF suggested).

6.2.

Analog Mixer Output

The mixer generates three distinct outputs:

•

A stereo mix of all sources for output to the LINE_OUT and HP_OUT

•

A stereo mix of all analog sources for recording

•

Microphone only or mono mix of all sources for MONO_OUT

Note: Mono output of stereo mix is attenuated by -6 dB.

6.3.

SPDIF Digital Mux

The STAC9750/9751 incorporates a digital output that supports SPDIF formats. A multiplexer deter-

mines which of two digital input streams are used for the digital output conversion process. These

two streams include the PCM OUT data from the audio controller and the ADC recorded output. The

normal analog LINE_OUT signal can be converted to the SPDIF formats by using the internal ADC

to record the “MIX” output, which is the combination of all analog and all digital sources. In the case

of digital controllers with support for 4 or more channels, the SPDIF output mode can be used to sup-

port compressed 6-channel output streams for delivery to home theater systems. These can be

routed on alternate AC-Link slots to the SPDIF output, while the standard 2-channel output is deliv-

ered as selected by bits D5 and D4 in Register 6E. If the digital controller supports 6 channels, a

SPDIF output with 4 analog channels can also be configured (in a multi-CODEC setup).

For more

information for SPDIF please see 6.5.12.2; page 44.

Pin 48: To Enable SPDIF, use an 1 K

Ω-10 KΩ external pulldown. To Disable SPDIF, use an

Ω-10 KΩ external pullup. Do NOT leave Pin 48 floating.

6.4.

PC Beep Implementation

PC Beep is active on power up and defaults to an un-muted state. The PC_BEEP input is routed

directly to the MONO_OUT, LINE_OUT and HP_OUT pins of the CODEC. Because the PC_BEEP

input drive is often a full scale digital signal, some resistive attenuation of the PC_BEEP input is rec-

ommended to keep the beep tone within reasonable volume levels. The user should mute this input

before using any other mixer input because the PC Beep input can contribute noise to the lineout

during normal operation. This style of PC Beep is related to the AC’97 Specification Rev 2.2. To use

the analog PC Beep, a value of 00h to bits F[7:0](D[12:5]) disables the Digital PC Beep generation.

PV[3:0] (D[4:1]) controls the volume level from 0 to 45dB of attenuation in 3dB steps.

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