STAC9708 datasheet(34/56 Pages) ETC

34 / 56 page

SigmaTel, Inc.

Preliminary

STAC9708/11

10/02/98

NOTE: The lower half of the Vendor ID2 register (index 7Eh) currently contains the value 08h

identifying the STAC9708/11. This value can be used by the audio driver, or miniport driver in the

case of WIN98

, to adjust software functionality to match the feature-set of the STAC9708/11. This

portion of the register will likely contain different values if the software profile of the STAC9708/11

changes, as in the case of silicon level device modifications. This will allow the software driver to

identify any required operational differences between the existing STAC9708/11 and any future

versions.

5. LOW POWER MODES

The STAC9708/11 is capable of operating at reduced power when no activity is required. The state of power

down is controlled by the Powerdown Register (26h). There are 7 commands of separate power down. The

power down options are listed in Table 18. The first three bits , PR0..PR2, can be used individually or in

combination with each other, and control power distribution to the ADC’s, DAC’s and Mixer. The last analog

power control bit, PR3, affects analog bias and reference voltages, and can only be used in combination with PR1,

PR2, and PR3. PR3 essentially removes power from all analog sections of the codec, and is generally only

asserted when the codec will not be needed for long periods. PR0 and PR1 control the PCM ADC’s and DAC’s

only. PR2 and PR3 do not need to be "set" before a PR4, but PR0 and PR1 must be "set" before PR4.

Table 20. Low Power Modes

GRP BITS

FUNCTION

PR0

PCM in ADC’s & Input Mux Powerdown

PR1

PCM out DACs Powerdown

PR2

Analog Mixer powerdown (Vref still on)

PR3

Analog Mixer powerdown (Vref off)

PR4

Digital Interface (AC-Link) powerdown (extnl clk off)

PR5

Internal Clk disable

PR6

Not implemented

PRJ

Powerdown Surround DACs

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