STAC9721 datasheet(22/48 Pages) ETC1

22 / 48 page

SigmaTel, Inc.

Data Sheet

STAC9721

04/07/00

4.4.1 Reset Register (Index 00h)

Writing any value to this register performs a register reset, which causes all registers to

revert to their default values. This register returns the AC’97 ID code of the part when

read.

4.4.2 Play Master Volume Registers (Index 02h, 04h, and 06h)

These registers manage the output signal volumes. Register 02h controls the stereo

master volume (both right and left channels), register 04h controls the optional stereo true

line level out, and register 06h controls the mono volume output. Each step corresponds

to 1.5 dB. The MSB of the register is the mute bit. When this bit is set to 1 the level for

that channel is set at -

∞ dB. ML5 through ML0 is for left channel level, MR5 through

MR0 is for the right channel and MM5 through MM0 is for the mono out channel. If

optional bits D13 and D5 of register 02h and 04h, or D5 of register 06h are set to 1, then

the corresponding attenuation is set to 46dB and the register reads will produce 1Fh as a

value for this attenuation/gain block

Table 8. Play Master Volume Register

Mute

Mx5…Mx0

Function

Range

00 0000

0dB Attenuation

Req.

01 1111

46.5 Attenuation

Req.

xx xxxx

∞ dB

Attenuation

Req.

4.4.3 PC Beep Register (Index 0Ah)

This register controls the level for the PC Beep input. Each step corresponds to

approximately 3 dB of attenuation. The MSB of the register is the mute bit. When this

bit is set to 1 the level for that channel is set at -

∞ dB. PC_BEEP supports motherboard

implementations. The intention of routing PC_BEEP through the STAC9721/23 mixer is

to eliminate the requirement for an onboard speaker by guaranteeing a connection to

speakers connected via the output jack. In order for this to be viable the PC_BEEP signal

needs to reach the output jack at all times. NOTE: the PC_BEEP is routed to L & R

Line outputs even when the STAC9721/23 is in a RESET state. This is so that Power On

Self Test (POST) codes can be heard by the user in case of a hardware problem with the

PC. For further PC_BEEP implementation details please refer to the AC'97 Technical

FAQ sheet. The default value of 0000h corresponds to 0 dB attenuation with mute off.

Table 9. PC_BEEP Register

Mute

PV3…PV0

Function

0000

0 dB Attenuation

1111

45 dB Attenuation

xxxx

∞ dB Attenuation

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