STAC9708 datasheet(33/56 Pages) ETC

33 / 56 page

SigmaTel, Inc.

Preliminary

STAC9708/11

10/02/98

4.4.10.1

External Amplifier Power Down Control

The EAPD bit 15 of the Powerdown Control/Status Register (Index 26h) directly controls the output of

the EAPD output, pin 45, and produces a logical “1” when this bit is set to logic high. This function is

used to control an external audio amplifier power down. EAPD = 0 places approximately 0V on the

output pin, enabling an external audio amplifier. EAPD = 1 places approximately DVdd on the output

pin, disabling the external audio amplifier. Audio amplifiers that operate with reverse polarity will

likely require an external inverter to maintain software driver compatibility.

4.4.11 Extended Audio ID Register (Index 28)

The Extended Audio ID register is a read only register used to communicate information to the digital

controller on two functions. ID1 and ID0 echo the configuration of the codec as defined by the

programming of pins 47 and 48 externally. “00” returned defines the codec as the primary codec, while

any other code identifies the codec as one of three secondary codec possibilities. SDAC=1 tells the

controller that the STAC9708 is a multi-channel codec as defined by the Intel spec.

4.4.12 Extended Audio Status Register (Index 2Ah)

The Extended Audio Status Control register contains two active bits for powerdown and status of the

surround DACs. PWD is a read/write bit which is used to powerdown the surround DACs, and SDAC a

read only bit to tell the controller when the surround DACs are ready to receive data.

4.4.13 Analog Special Register (Index 6Ch)

The Analog Special Register has two read/write bits used to control two functions specific to the

STAC9708. DAC –6dB is used to program the DAC outputs to a –6dB signal level relative to the value

of gain already programmed. Similarly, ADC –6dB attenuates any signal input to the ADC by 6dB. This

second function is very useful in applications with greater than 1Vrms input levels, as is the case with

many CDROMs.

4.4.14 Vendor ID1 and ID2 (Index 7Ch and 7Eh)

These two registers contain four 8-bit ID codes. The first three codes have been assigned by Microsoft

using their Plug and Play Vendor ID methodology. The fourth code is a SigmaTel, Inc. assigned code

identifying the STAC9708/11. The ID1 register (index 7Ch) contains the value 8384h, which is the

first (83h) and second (84h) characters of the Microsoft

ID code.

The ID2 register (index 7Eh)

contains the value 7608h, which is the third (76h) of the Microsoft

ID code, and 08h which is the

STAC9708/11 ID code.

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