CS42428 datasheet(25/73 Pages) CIRRUS

25 / 73 page

DS605F1

CS42428

When the device is clocked from OMCK, the frequency of OMCK must be at least twice the frequency of

the fastest Slave Mode, SCLK. For example, if both serial ports are in Slave Mode with one SCLK running

at 32x Fs and the other at 64x Fs, the slowest OMCK signal that can be used to clock the device is

128x Fs.

When either serial port is in Slave Mode, its respective LRCK signal must be present for proper device

operation.

In Slave Mode, One-Line Mode #1 is supported; One-Line Mode #2 is not.

The sample rate to OMCK ratios and OMCK frequency requirements for Slave Mode operation are shown

in Table 1. Refer to Table 3 for required clock ratios.

4.5

Digital Interfaces

4.5.1

Serial Audio Interface Signals

The CS42428 interfaces to an external Digital Audio Processor via two independent serial ports, the

DAC serial port, DAC_SP, and the ADC serial port, ADC_SP. The digital output of the internal ADCs use

the ADC_SDOUT pin and can be configured to use either the ADC or DAC serial port timings.These con-

figuration bits and the selection of Single-, Double- or Quad-Speed Mode for DAC_SP and ADC_SP are

found in register “Functional Mode (address 03h)” on page 43.

The serial interface clocks, ADC_SCLK for ADC_SP and DAC_SCLK for DAC_SP, are used for transmit-

ting and receiving audio data. Either ADC_SCLK or DAC_SCLK can be generated by the CS42428 (Mas-

ter Mode), or it can be input from an external source (Slave Mode). Master or Slave Mode selection is

made using bits DAC_SP M/S and ADC_SP M/S in register “Misc Control (address 05h)” on page 46.

The Left/Right clock (ADC_LRCK or DAC_LRCK) is used to indicate left and right data frames and the

start of a new sample period. It may be an output of the CS42428 (Master Mode), or it may be generated

by an external source (Slave Mode). As described in later sections, particular modes of operation do allow

the sample rate, Fs, of the ADC_SP and the DAC_SP to be different, but must be multiples of each other.

The serial data interface format selection (Left/Right-Justified, I²S or One-Line Mode) for the ADC serial

port data out pin, ADC_SDOUT, and the DAC input pins, DAC_SDIN1:4, is configured using the appro-

priate bits in the register “Interface Formats (address 04h)” on page 45. The serial audio data is presented

in two's complement binary form with the MSB first in all formats.

DAC_SDIN1, DAC_SDIN2, DAC_SDIN3and DAC_SDIN4 are the serial data input pins supplying the in-

ternal DAC. ADC_SDOUT, the ADC data output pin, carries data from the two internal 24-bit ADCs and,

when configured for one-line mode, up to four additional ADC channels attached externally to the signals

ADCIN1 and ADCIN2 (typically two CS5361 stereo ADCs). When operated in One-Line Mode, 6 channels

of DAC data are input on DAC_SDIN1, two additional DAC channels on DAC_SDIN4, and 6 channels of

ADC data are output on ADC_SDOUT. Table 4 on page 26 outlines the serial port channel allocations.

Single-Speed

Double-Speed

Quad-Speed

One-Line Mode #1

OMCK/LRCK Ratio

256x, 384x, 512x

128x, 192x, 256x

64x, 96x, 128x

256x

SCLK/LRCK Ratio

32x, 48x, 64x, 128x

32x, 48x, 64x

128x

Table 3. Slave Mode Clock Ratios

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