AD1985

Rev. A | Page 44 of 48

Information and I/O Register (Index 0x68, Page 01)

Reg Num

Name

D15 D14 D13 D12 D11 D10 D9

D8

D7

D6

D5

D4 D3 D2 D1 D0 Default

0x68

Function Information

G4

G3

G21

G1

G0

INV

DL4 DL3 DL2 DL1 DL0 IV

X

X

X

FIP N/A

New register added for AC ’97 2.3.

Data read back from this register is invalid unless a function is first specified in Register 0x66, page 01.

Gain Bits. (Read/write.)

The codec updates these bits with the gain value (dB relative to level out) in 1.5 dBV increments, not including the volume

control gains. For example, if the volume gain is 0 dB, then the output pin should be 0 dB level. Any difference is the gain

reflected here. When relevant, the BIOS further updates these bits to take into consideration external amplifiers or other

external logic that it knows about. G[3:0] indicates the magnitude of the gain. G[4] indicates whether the value is a gain or

attenuation—essentially a sign bit.

G[4:0]

Gain or Attenuation (dB Relative to Level Out)

0 0000

0 dBV

0 0001

1.5 dBV

0 1111

24 dBV

1 0001

–1.5 dBV

G[4:0]

1 1111

–24 dBV

Inversion Bit. (Read/write.) Indicates that the codec presents a 180° phase shift to the signal.

0: No inversion reported.

INV

1: Inverted.

Buffer Delays (read/write) The default value is the delay internal to the codec. The BIOS may add to this value the known

delays external to the codec, such as for an external amplifier, logic, etc.

The codec provides a number representing a delay measurement for the input and output channels. Software will use this

value to accurately calculate the audio stream position with respect to what has been reproduced or recorded. These values

are in 20.83 µs (1/48000 second) units.

For output channels, this timing is from the end of the AC link frame in which the sample is provided, until the time the

analog signal appears at the output pin. For input streams, this is from when the analog signal is presented at the pin until the

representative sample is provided on the AC link. Analog-to-analog paths are not considered in this measurement. The

measurement is a typical measurement, at a 48 kHz sample rate, with minimal in-codec processing.

0x00: Information not provided.

0x01 to 0x1E: Buffer delay in 20.83 µs units.

DL[4:0]

0x1F: Reserved.

IV

Information Valid Bit. Indicates whether a sensing method is provided by the codec and if information field is valid. This field

is updated by the codec.

0: (A) After codec reset de-assertion, it indicates the codec does not provide sensing logic and this bit will be read-only.

(B) After a sense cycle is completed, indicates that no information is provided on the sensing method.

1: (A) After codec reset de-assertion, it indicates the codec provides sensing logic for this I/O and this bit is read/write.

(B) After clearing this bit by writing 1, when a sense cycle is completed, indicates that there is valid information in the

remaining descriptor bits. Writing 0 to this bit has no effect.

FIP

Function Information Present. (Read-only.)

1: The G[4:0], INV, and DL[4:0] (in Register 0x68) bits and the ST[2:0] (in Register 0x6A) bits are supported and are read/write

capable.

0: The G[4:0], INV, DL[4:0], and ST[2:0] bits are not supported and are read-only with a value of 0.