CS42L51 Datasheet, PDF (39/83 Pages) Cirrus Logic – Low Power, Stereo CODEC with Headphone Amp

4.5.4
CS42L51
Quarter- and Half-Speed Mode
Quarter-Speed Mode (QSM) and Half-Speed Mode (HSM) allow lower sample rates while maintaining a
relatively flat noise floor in the typical audio band of 20 Hz - 20 kHz. Single-Speed Mode (SSM) will allow
lower frequency sample rates; however, the DAC's noise floor, that normally rises out-of-band, will scale
with the lower sample rate and begin to rise within the audio band. QSM and HSM corrects for most of
this scaling, effectively increasing the dynamic range of the CODEC at lower sample rates, relative to
SSM.
4.6 Digital Interface Formats
The serial port operates in standard I²S, Left-Justified or Right-Justified(DAC only) digital interface formats
with varying bit depths from 16 to 24. Data is clocked out of the ADC or into the DAC on the rising edge of
SCLK. Figures 20-22 illustrate the general structure of each format. Refer to “Switching Specifications - Se-
rial Port” on page 20 for exact timing relationship between clocks and data.
Software
Control:
“Interface Control (Address 04h)” on page 49.
Hardware
Pin
Control: _{“I²S/LJ” pin 3}
Setting
LO
Selection
Left-Justified Interface
HI
I²S Interface
LRCK
SCLK
SDIN
SDOUT
MSB
Left Channel
AOUTA / AINxA
LSB
MSB
Figure 20. I²S Format
Right Channel
AOUTB / AINxB
LRCK
SCLK
SDIN
SDOUT
MSB
Left Channel
Right Channel
AOUTA / AINxA
LSB
MSB
AOUTB / AINxB
Figure 21. Left-Justified Format
LSB
MSB
LSB
MSB
LRCK
SCLK
SDIN
Left Channel
Right Channel
MSB
LSB
MSB
LSB
AOUTA
AOUTB
Figure 22. Right-Justified Format (DAC only)
DS679A2
39