cs4239 Cirrus Logic, Inc., cs4239 Datasheet - Page 70

• Manufacturer Part Number: cs4239
• Description: Crystalclear? Ortable Isa Audio System Logic
• Manufacturer: Cirrus Logic, Inc.

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-
2) During a single write cycle, change the Clock
3) The WSS Codec resynchronizes its internal
4) The host now polls the WSS Codec’s Index
5) Once the WSS Codec is no longer responding
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
70
able using the MCE bit of the Index Address
register (R0).
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.)
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.
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).
to reads with a value of 80 hex, normal op-
eration can resume and the WSS Codec can
be removed from MCE.
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.
CrystalClear Portable ISA Audio System
TM
CS4239
DS253PP2