CS6403 datasheet(27/54 Pages) CIRRUS

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Increase Volume (110)

Setting GPIN2/1/0 to 110 for 375

µS will decre-

ment the volume increment counter by one step

causing an increase in the SPKROUT volume.

To increase volume again, the GPIN2/1/0 pins

must be changed to another state before return-

ing to 110.

See section entitled "Volume

Control/ AGC" for more details.

Decrease Volume (101)

Setting GPIN2/1/0 to 101 for 375

µS will incre-

ment the volume increment counter by one step

causing an decrease in the SPKROUT volume.

To decrease volume again, the GPIN2/1/0 pins

must be changed to another state before return-

ing to 101. The section below entitled "Volume

Control/AGC" explains this function in greater

detail.

Don’t Care (010, 100)

When the GPIN2/1/0 pins are set to 010, or 100,

the CS6403 ignores the input. This state is pro-

vided in order to provide a "resting place"

between consecutive volume increase or volume

decrease requests.

Volume Control/AGC

The SPKROUT volume control of the CS6403 is

implemented in two stages: the upper ten volume

increments are implemented by a software peak-

limiting automatic gain control (AGC); the lower

32 volume increments are controlled by a hard-

ware DAC attenuation stage with software

compensation at the adaptive filter to avoid

changing the echo path. The volume increments

range from 0 (loudest) to 41 (quietest).

The AGC works by comparing the digital codes

coming from SDI to a threshold value, and if the

signal amplitude is greater than the threshold, it

is scaled down to the threshold. These signals

are subsequently scaled up so that the threshold

is full scale.

The threshold value which is

roughly determined by the formula: Threshold =

Full Scale - (10 - Volume Increment) x 3dB. For

example, a volume increment of 0 (the loudest

output volume possible) would force signals

greater than 30dB below full scale (10 x 3dB) to

30dB below full scale and then scale all signals

up 30dB so that 30dB below full scale becomes

full scale.

When the AGC is controlling the output volume,

the steps are effectively 3dB per volume incre-

ment. Note that if the signals are already strong,

increasing the volume may not make the sound

any louder since they are already being scaled up

to full scale. Also note that the AGC is effec-

tively disabled by setting the volume increment

to 10. The default volume increment (set upon

reset) is 4.

When the DAC attenuation stage is controlling

the output volume, the step size is 2.5dB per

volume increment. The 32 steps (from volume

increment 10 to 41) yield up to 77.5dB of addi-

tional attenuation.

Note that if the AGCD (SSI_CR1.10) is set in

Mode 2 (16-bit), then the DAC is attenuated by

10 dB (4 x 2.5 dB), and the effective volume

control range is from volume increment 0 to 31,

with each increment equal to 2.5 dB of attenu-

ation.

The volume increment defaults to 4 upon reset.

If an attempt is made to increase volume beyond

volume increment 0, the GPOUT0 pin will go

high for 125

µS. GPOUT0 will also go high if

an attempt is made to decrease volume beyond

volume increment 41.

CS6403

DS192PP6

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