Applications, 1 three-wire serial input/output audio port – Cirrus Logic CS8421 User Manual
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DS641F6
CS8421
4. APPLICATIONS
The CS8421 is a 32-bit, high-performance, monolithic CMOS stereo asynchronous sample-rate converter.
The digital audio data is input and output through configurable 3-wire serial ports. The digital audio input/output ports
offer Left-Justified, Right-Justified, and I²S serial audio formats. The CS8421 also supports a TDM Mode which al-
lows multiple channels of digital audio data on one serial line. A Bypass Mode allows the data to be passed directly
to the output port without sample rate conversion.
The CS8421 does not require a control port interface, helping to speed design time by not requiring the user to de-
velop software to configure the part. Pins that are sensed after reset allow the part to be configured. See
Power-Down, and Start-Up” on page 22
Target applications include digital recording systems (DVD-R/RW, CD-R/RW, PVR, DAT, MD, and VTR), digital mix-
ing consoles, high quality D/A, effects processors and computer audio systems.
and
show the supply and external connections to the CS8421.
4.1
Three-wire Serial Input/Output Audio Port
A 3-wire serial audio input/output port is provided. The interface format should be chosen to suit the attached device
through the MS_SEL, SAIF, and SAOF pins.
show the pin functions and their corresponding set-
tings. The following parameters are adjustable:
•
Master or Slave
•
Master clock (MCLK) frequencies of 128*Fsi/o, 256*Fsi/o, 384*Fsi/o, and 512*Fsi/o (Master Mode)
•
Audio data resolution of 16-, 20-, 24-, or 32-bits
•
Left- or Right-Justification of the data relative to left/right clock (LRCK) as well as I²S
show the input/output formats available.
In Master Mode, the left/right clock and the serial bit clock are outputs, derived from the XTI input pin master clock.
In Slave Mode, the left/right clock and the serial bit clock are inputs and may be asynchronous to the XTI master
clock. The left/right clock should be continuous, but the duty cycle can be less than 50% if enough serial clocks are
present in each phase to clock all of the data bits.
ISCLK is always set to 64*Fsi when the input is set to master. In normal operation, OSCLK is set to 64*Fso. In TDM
Slave Mode, OSCLK must operate at N*64*Fso, where N is the number of CS8421’s connected together. In TDM
Master Mode, OSCLK is set to 256*Fso
For more information about serial audio formats, refer to the Cirrus Logic applications note AN282, “The 2-Channel
Serial Audio Interface: A Tutorial”, availa
.