Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0

5.7.1 Reset Register (Index 00h)

Reg Name D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Default

00h Reset X SE4 SE3 SE2 SE1 SE0 ID9 ID8 ID7 ID6 ID5 ID4 ID3 ID2 ID1 ID0 na

Reading this register returns the ID code of the part and a code for the type of 3D Stereo Enhancement, if any.

Writing any value to this register performs an audio register reset, which causes all audio registers to revert to their

default values. The ID defines the capabilities of AC ‘97 based on the following:

Bit = 1 Function

ID0 Dedicated Mic PCM In channel

ID1 Reserved (was Modem Line Codec support)

ID2 Bass & Treble control

ID3 Simulated Stereo (Mono to Stereo)

ID4 Headphone out support (not LNLVL or 4CH)

ID5 Loudness (bass boost) support

ID6 18 bit DAC resolution

ID7 20 bit DAC resolution

ID8 18 bit ADC resolution

ID9 20 bit ADC resolution

Table 17. Baseline Audio Optional Feature IDs

All DACs operate at the same resolution. All ADCs operate at the same resolution.

The standard AC ‘97 DAC and ADC resolutions are defined as 16-bits. 18- or 20-bit resolution implementations are

optional. The audio driver for an “enhanced” AC ‘97 Controller can determine the implemented DAC and ADC

resolution after it has been loaded by reading the AC ‘97 Codec’s Reset Register which is located at 0x00. If, for

example, the driver has determined that the implemented DAC resolution is 16-bits yet the Controller supports 18-

or 20-bit sample streams for playback, the Controller can either dither the sample streams down to 16-bits or pass

the stream “as is”. Since all AC-link data time slots carry 20 bits, the non-dithered approach will result in the least

significant bits which overrun the DAC width being dropped. For this reason dithering may be an attractive feature

for the Controller that supports greater than 16-bit sample streams.

The 3D stereo enhancement decodes are based on Table 18, AC ‘97 48-pin package pinlist. Note that the 3D control

center and depth, but can also be used generically. The 3D Control Register should be read to determine if the

selected enhancement is either fixed or variable center and depth. If the lower 8-bits of the 3D Control Register are

non-zero, then the depth/generic1 control is fixed; otherwise it is variable. If the upper 8-bits of the 3D Control