CS4239 datasheet(70/98 Pages) CIRRUS

70 / 98 page

Changing Sampling Rate

The internal states of the WSS Codec are syn-

chronized by the selected sampling frequency.

The sample frequency can be set in one of three

fashions. The standard WSS Codec method uses

the Fs & Playback Data Format register (I8) to

set the sample frequency. The changing of either

the clock source or the clock frequency divide

requires a special sequence for proper WSS

Codec operation:

1) Place the WSS Codec in Mode Change En-

able using the MCE bit of the Index Address

2) During a single write cycle, change the Clock

Frequency Divide Select (CFS) and/or

Clock 2 Base Select (C2SL) bits of the Fs &

Playback Data Format register (I8) to the de-

sired value. (The data format may also be

changed.)

3) The WSS Codec resynchronizes its internal

states to the new frequency. During this time

the WSS Codec will be unable to respond.

Writes to the WSS Codec will not be recog-

nized and reads will always return the value

80 hex.

4) The host now polls the WSS Codec’s Index

Address register (R0) until the value 80 hex

is no longer returned. On slow processor sys-

tems, 80h may occur faster than software is

able to read (80h may never occur).

5) Once the WSS Codec is no longer responding

to reads with a value of 80 hex, normal op-

eration can resume and the WSS Codec can

be removed from MCE.

A second method of changing the sample fre-

quency is to disable the sample frequency bits in

I8 (lower four bits) by setting SRE in I22. When

this bit is set, OSM1 and OSM0 in I10, along

with the rest of the bits in I22, are used to set the

sample frequency. Once enabled, these bits can

be changed without doing an MCE cycle.

The third method supports independent sample

frequencies (Fs) for capture and playback. The

independent sample frequency mode is enabled

by setting IFSE in X11. Once enabled, the other

two methods for setting Fs (I8, I10, and I22) are

disabled. The capture (ADC) Fs is set in X12

and the playback (DAC) Fs is set in X13.

Changing Audio Data Formats

In MODE 1, MCE must be used to select the

audio data format in I8. Since MCE causes a

calibration cycle, it is not ideal for full-duplex

operation. In MODE 2 and 3, individual Mode

Change Enable bits for capture and playback are

provided in register I16. MCE (R0) must still be

used to select the sample frequency, but PMCE

(playback) and CMCE (capture) allow changing

the respective data formats without causing a

calibration to occur. Setting PMCE (I16) clears

the playback FIFO and allows the upper four

bits of I8 to be changed. Setting CMCE (I16)

clears the capture FIFO and allows the upper

four bits of I28 to be changed.

Audio Data Formats

The sample frequency is always selected in the

Fs & Playback Data Format register (I8). In

MODE 1 the same register, I8, determines the

audio data format for both playback and capture;

however, in MODE 2 and 3, I8 only selects the

playback data format and the capture data format

is independently selectable in the Capture Data

Format register (I28).

The WSS Codec always orders the left channel

data before the right channel. Note that these

definitions apply regardless of the specific for-

mat of the data. For example, the left sample

always comes first in the data stream regardless

of whether the sample is 16-bit or 8-bit in size.

DS253PP2

CS4239

CrystalClear Portable ISA Audio System

CS4239 Datasheet(PDF) 70 Page - Cirrus Logic

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